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Volume 25 Issue 9
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Original Articles
Integrable Rosochatius Deformations of the Restricted cKdV Flows
DAI Ji-Long, ZHOU Ru-Guang
Chin. Phys. Lett. 2008, 25 (9): 3095-3098 .  
Abstract   PDF(pc) (113KB) ( 489 )
Three novel finite-dimensional integrable Hamiltonian systems of Rosochatius type and their Lax representations are presented. We make a deformation for the Lax matrixes of the Neumann type, the Bargmann type and the high-order symmetry type of restricted cKdV flows by adding an additional term and then prove that this kind of deformation does not change the r-matrix relations. Finally the new integrable systems are generated from these deformed Lax matrices.
Stability Analysis of an Inverted Pendulum Subjected to Combined High Frequency Harmonics and Stochastic Excitations
HUANG Zhi-Long, JIN Xiao-Ling, ZHU Zi-Qi
Chin. Phys. Lett. 2008, 25 (9): 3099-3102 .  
Abstract   PDF(pc) (349KB) ( 1048 )
Stability of vertical upright position of an inverted pendulum with its suspension point subjected to high frequency harmonics and stochastic excitations is investigated. Two classes of excitations, i.e., combined high frequency harmonic excitation and Gaussian white noise excitation, and high frequency bounded noise excitation, respectively, are considered. Firstly, the terms of high frequency harmonic excitations in the equation of motion of the system can be set equivalent to nonlinear stiffness terms by using the method of direct separation of motions. Then the stochastic averaging method of energy envelope is used to derive the averaged Itô stochastic differential equation for system energy. Finally, the stability with probability 1 of the system is studied by using the largest Lyapunov exponent obtained from the averaged Itô stochastic differential equation. The effects of system parameters on the stability of the system are discussed, and some examples are given to illustrate the efficiency of the proposed procedure.
A Field Method for Integrating Equations of Motion of Nonlinear Mechanico-Electrical Coupling Dynamical Systems
FU Jing-Li, FU Hao
Chin. Phys. Lett. 2008, 25 (9): 3103-3106 .  
Abstract   PDF(pc) (108KB) ( 525 )
We deal with the generalization of the field method to weakly non-linear mechanico-electrical coupling systems. The field co-ordinates and field momenta approaches are combined with the method of multiple time scales in order to obtain the amplitudes and phase of oscillations in the first approximation. An example in mechanico-electrical coupling systems is given to illustrate this method.
Modified Khaneja--Glaser Decomposition and Realization of Three-Qubit Quantum Gate
WEI Hai-Rui, DI Yao-Min, ZHANG-Jie
Chin. Phys. Lett. 2008, 25 (9): 3107-3110 .  
Abstract   PDF(pc) (119KB) ( 520 )

Optimal implementation of quantum gates is crucial for realization of quantum computation. We slightly modify the Khaneja--Glaser decomposition (KGD) for n-qubits and give a new Cartan subalgbra in the second step of the decomposition. Based on this modified KGD, we investigate the realization of three-qubit logic gate and obtain the result that a general three-qubit quantum logic gate can be implemented using at most 73 one-qubit gates rotations with respect to the y and z axes and 26 CNOT gates.

Eigenvalue Problems of non-Hermitian Systems via Improved Asymptotic Iteration Method
Okan Ö, zer
Chin. Phys. Lett. 2008, 25 (9): 3111-3114 .  
Abstract   PDF(pc) (100KB) ( 691 )
We simply use the relation between the asymptotic iteration method and the Nikiforov--Uvarov method for the analytical solution of the second order linear ordinary differential equations. We apply this relation to study the Schrödinger equation with potentials admitting quasinormal modes. Non-Hermitian PT symmetric potentials have also been studied. Energy eigenvalues in all the cases by the relation are found to be consistent with exact results
Sudden Death, Birth and Stable Entanglement in a Two-Qubit Heisenberg XY Spin Chain
SHAN Chuan-Jia, CHENG Wei-Wen, LIU Tang-Kun, LIU Ji-Bing, WEI Hua
Chin. Phys. Lett. 2008, 25 (9): 3115-3118 .  
Abstract   PDF(pc) (158KB) ( 623 )
Taking the decoherence effect due to population relaxation into account, we investigate the entanglement properties for two qubits in the Heisenberg XY interaction and subject to an external magnetic field. It is found that the phenomenon of entanglement sudden death (ESD) as well as sudden birth (ESB) appear during the evolution process for particular initial states. The influence of the external magnetic field and the spin environment on ESD and ESB are addressed in detail. It is shown that the concurrence, a measure of entanglement, can be controlled by tuning the parameters of the spin chain, such as the anisotropic parameter, external magnetic field, and the coupling strength with their environment. In particular, we find that a critical anisotropy constant exists, above which ESB vanishes while ESD appears. It is also notable that stable entanglement, which is independent of different initial states of the qubits, occurs even in the presence of decoherence.
Spectator Model Dynamics in a Leakage Cavity
JING Jun, LÜ, Zhi-Guo, YUAN Xiao-Zhong, MA Hong-Ru
Chin. Phys. Lett. 2008, 25 (9): 3119-3122 .  
Abstract   PDF(pc) (172KB) ( 452 )
A spectator system in an atoms-cavity QED model is investigated. The subsystem initial state is prepared as one of the Bell states or one mixed state. It is shown that (i) the dynamics of Bell states are independent on the initial states; (ii) the concurrence dynamics can be engineered by a controlling light field.
Scheme for Direct Measurement of the Wigner Function via Resonant Interaction
ZHENG Shi-Biao
Chin. Phys. Lett. 2008, 25 (9): 3123-3125 .  
Abstract   PDF(pc) (87KB) ( 406 )
We propose a scheme for direct measurement of the Wigner function for a cavity mode. In the scheme the cavity field resonantly interacts with an atomic ensemble. Under certain conditions, the state of the cavity mode is transferred to the atomic system. After a displacement the measurement of the parity of the atomic excitation number directly yields the Wigner function of the initial state of the cavity mode.
Fluctuation of Mesoscopic RLC Circuit at Finite Temperature
ZHANG Xiao-Yan, WANG Ji-Suo, FAN Hong-Yi
Chin. Phys. Lett. 2008, 25 (9): 3126-3128 .  
Abstract   PDF(pc) (100KB) ( 645 )
We consider the fluctuation of mesoscopic RLC circuit at finite temperature since a resistance always produces Joule heat when the circuit is working. By virtue of the thermo field dynamics and the coherent thermo state representation we show that the quantum mechanical zero-point fluctuations of both charge and current increase with the rising temperature and the resistance value.
Variational Study on a Dissipative Two-Level System
ZHU Wei-Ting, REN Qing-Bao, CHEN Qing-Hu,
Chin. Phys. Lett. 2008, 25 (9): 3129-3131 .  
Abstract   PDF(pc) (105KB) ( 591 )
A new variational approach is proposed to study the ground-state of a two-level system coupled to a dispersionless phonon bath. By the extended coherent state, where the more phonon correlations are easily incorporated, we can obtain very accurate ground state energy and the tunnelling reduction factor in all regime of tunnelling matrix element Δ0 and coupling parameter s. The relative difference between the present ones and those by exact numerical diagonalization is less then 0.001%. In addition, some simple analytical results are given in the limits of Δ0/s →0 and ∞.
One-Step Generation of Cluster States Assisted by a Strong Driving Classical Field in Cavity Quantum Electrodynamics
SHAO Xiao-Qiang, ZHANG Shou
Chin. Phys. Lett. 2008, 25 (9): 3132-3134 .  
Abstract   PDF(pc) (94KB) ( 604 )

We propose a scheme for one-step generation of cluster states with atoms sent through a thermal cavity with strong classical driving field, based on the resonant atom--cavity interaction so that the operating time is sharply short, which is important in the view of decoherence.

Performance of Differential-Phase-Shift Keying Protocol Applying 1310nm Up-Conversion Single-Photon Detector
FENG Chen-Xu, JIAO Rong-Zhen, ZHANG Wen-Han
Chin. Phys. Lett. 2008, 25 (9): 3135-3137 .  
Abstract   PDF(pc) (188KB) ( 545 )
The performance of the differential-phase-shift keying (DPSK) protocol applying a 1310 nm up-conversion single-photon detector is analysed. The error rate and the communication rate as a function of distance for three quantum key distribution protocols, the Bennett--Brassard 1984, the Bennett--Brassard--Mermin 1992, and the DPSK, are presented. Then we compare the performance of these three protocols using the 1310nm up-conversion detector. We draw the conclusion that the DPSK protocol applying the detector has significant advantage over the other two protocols. Longer transmission distance and lower error rate can be achieved.
Secret Key Distillation for Continuous Variable Quantum Key Distribution against Gaussian Classical Eve
ZHAO Yi-Bo, HAN Zheng-Fu, CHEN Jin-Jian, GU You-Zhen, GUO Guang-Can
Chin. Phys. Lett. 2008, 25 (9): 3138-3141 .  
Abstract   PDF(pc) (245KB) ( 501 )

The continuous variable quantum key distribution is expected to provide high secret key rate without single photon source and detector, while the lack of the effective key distillation method makes it unpractical under the high loss condition. Here we present a single-bit-reverse-reconciliation protocol against Gaussian classical Eve, which can distill the secret key through practical imperfect error correction with high efficiency. The simulation results show that this protocol can distill secret keys even when the transmission fibre is longer than 150 km, which may make the continuous variable scheme to outvie the single photon one.

Concentration of Unknown Atomic Entangled States via Entanglement Swapping through Raman Interaction
ZOU Jin-Hua, HU Xiang-Ming
Chin. Phys. Lett. 2008, 25 (9): 3142-3145 .  
Abstract   PDF(pc) (96KB) ( 467 )
We show that entanglement concentration of unknown atomic entangled states is achieved via the implementation of entanglement swapping based on Raman interaction in cavity QED. A maximally entangled state is obtained from a pair of partially entangled states probabilistically. Due to Raman
interaction of two atoms with a cavity mode and an external driving field, the influence of atomic spontaneous emission has been eliminated. Because of the virtual excitation of the cavity mode, the decoherence of cavity decay and thermal field is neglected.
Effects of Purity on Dynamics of Multipartite Entanglement
ZHANG Yu-Shi
Chin. Phys. Lett. 2008, 25 (9): 3146-3149 .  
Abstract   PDF(pc) (2229KB) ( 432 )
We study the effects of purity on entanglement dynamics of a multipartite system in cavity QED. Three two-level atoms A, B and C are initially prepared in an entangled state and locally coupled with independent cavities a, b and c, respectively. We consider the effects of purity of atomic initial state on the entanglement evolution of both the systems of atoms and cavities. It is found that depending on the purity of atomic initial state, the entanglement of atoms (cavities) may or may not exhibit the sudden death (birth) phenomenon.
Robust Implementation of a Nonlocal N-Qubit Phase Gate by Interference of Polarized Photons
XIA Yan, SONG Jie, SONG He-Shan
Chin. Phys. Lett. 2008, 25 (9): 3150-3153 .  
Abstract   PDF(pc) (121KB) ( 472 )

We propose a protocol to directly implement the nonlocal phase gate of N λ-type three-level atoms trapped in distant cavities by using interference of polarized photons. The protocol uses the effects of quantum statistics of indistinguishable photons emitted by the atoms inside optical cavities.

Enhanced Quantum Reflection of Ultracold Atoms with Strong Interatomic Interaction
LIU Min, ZHAN Ming-Sheng
Chin. Phys. Lett. 2008, 25 (9): 3154-3157 .  
Abstract   PDF(pc) (124KB) ( 429 )

We calculate the reflection probability for ultracold alkali atoms incident on a solid surface. By considering the interatomic interaction and using the WKB method, it is shown that the repulsive interaction between atoms has the effect of increasing the reflection probability. The increasing amplitude is related with the interatomic interaction and the depth of atom-surface potential. In addition, we also perform a numerical calculation to testify the effect of the interatomic interaction, and the analytic result is proven by the numerical result.

Fission and Fusion of Two Bright Solitons in a Growing Bose--Einstein Condensate
HE Zhang-Ming, WANG Deng-Long, ZHANG Wei-Xi, WANG Feng-Jiao, DING Jian-Wen
Chin. Phys. Lett. 2008, 25 (9): 3158-3161 .  
Abstract   PDF(pc) (132KB) ( 472 )
We analytically study the interaction characteristics of two bright solitons in a one-dimensional growing Bose--Einstein condensate with time-dependent periodic atomic scattering length. It is shown that the interaction between two bright solitons can generate fission and fusion in the presence of both time-dependent periodic atomic scattering length and the growing case. Furthermore, we propose experimental protocols to realize these interaction phenomena by varying the scattering length via the Feshbach resonance in the future experiment.
A Kind of Exact Inflationary Solution in the Chaotic Inflation Model to Non-minimally Coupled Scalar Field
CHEN Shi-Wu, YANG Shu-Zheng, HAO Xi-Zhun, LIU Xiong-Wei
Chin. Phys. Lett. 2008, 25 (9): 3162-3164 .  
Abstract   PDF(pc) (103KB) ( 575 )

We present a kind of exact inflationary solution in the chaotic inflation scenario to non-minimal coupled scalar field, taking the Hubble parameter directly as a function of the scalar field φ, H(φ)=αφn. Using the analysis of the WMAP3 data, we give the range of power index n.

Properties of Hydrated Alkali Metals Aimed at the Ion Channel Selectivity
AN Hai-Long, LIU Yu-Zhi, ZHANG Su-Hua, ZHAN Yong, ZHANG Hai-Lin
Chin. Phys. Lett. 2008, 25 (9): 3165-3168 .  
Abstract   PDF(pc) (1518KB) ( 1706 )
The hydration structure properties of different alkali metal ions with eight water molecules and potassium ions with different numbers of water molecules are studied using the mixed density functional theory, B3LYP, with 6-311G basis set. The hydration structures are obtained from structure optimization and the optimum numbers of water molecules in the innermost hydration shell for the alkali metal ions are found. Some useful information about the ion channel selectivity is presented.
Hyperchaos--chaos--Hyperchaos Transition in a Class of On--Off Intermittent Systems Driven by a Family of Generalized Lorenz Systems
ZHOU Qian, CHEN Zeng-Qiang, YUAN Zhu-Zhi
Chin. Phys. Lett. 2008, 25 (9): 3169-3172 .  
Abstract   PDF(pc) (830KB) ( 670 )
Blowout bifurcation in nonlinear systems occurs when a chaotic attractor lying in some symmetric subspace becomes transversely unstable. A class of five-dimensional continuous autonomous systems is considered, in which a two-dimensional subsystem is driven by a family of generalized Lorenz systems. The systems have some common dynamical characters. As the coupling parameter changes, blowout bifurcations occur in these systems and brings on change of the systems' dynamics. After the bifurcation the phenomenon of on--off intermittency appears. It is observed that the systems undergo a symmetric hyperchaos--chaos--hyperchaos transition via or after blowout bifurcations. An example of the systems is given, in which the drive system is the Chen system. We investigate the dynamical behaviour before and after the blowout bifurcation in the systems and make an analysis of the transition process. It is shown that in such coupled chaotic continuous systems, blowout bifurcation leads to a transition from chaos to hyperchaos for the whole systems, which provides a route to hyperchaos
Soliton Structure of a Higher Order (2+1)-Dimensional Nonlinear Evolution Equation of Barothropic Relaxing Media beneath High-Frequency Perturbations
Bouetou Bouetou Thomas, , Kuetche Kamgang Victor, Timoleon Crepin Kofane,
Chin. Phys. Lett. 2008, 25 (9): 3173-3176 .  
Abstract   PDF(pc) (240KB) ( 402 )
From the dynamical equation of barothopic relaxing media beneath pressure perturbations, followed with the reductive perturbative analysis, we derive and investigate the soliton structure of a (2+1)-dimensional nonlinear evolution equation describing high-frequency regime of perturbations. Thus, by means of the Hirota's bilinearization method, we unearth three typical patterns of loop-, cusp- and hump-like shapes depending strongly upon a dissipation parameter.
Development of Simple Dip-Stick-Type Uniaxial Stress Actuator for Alternating-Current Susceptibility Measurements
MYDEEN Kamal, YU Yong, JIN Chang-Qing
Chin. Phys. Lett. 2008, 25 (9): 3177-3180 .  
Abstract   PDF(pc) (673KB) ( 359 )
A simple dip-stick type uniaxial stress actuator for ac-susceptibility measurement is designed. Target pressure can be achieved by smooth and continues work carried out using a combination of light weight micrometer and spring. The magnitude of the pressure is directly calculated from the force constant of the spring and the surface area of the sample. Benchmark on the quality of the data under uniaxial pressure is confirmed by the Piezo resistance measurements on [100] oriented n-type Si. The system is examined and calibrated with the standard paramagnetic Gd2O3. Further, the device performance, generation of constant uniaxial pressure against temperature variations, is assured by investigating the ac-magnetic susceptibility measurements on highly anisotropic La1.25Sr1.75Mn2O7 bilayer single crystal.
Conservation Laws for Partially Conservative Variable Mass Systems via d'Alembert's Principle
AFTAB Ahmed, NASEER Ahmed, QUDRAT Khan
Chin. Phys. Lett. 2008, 25 (9): 3181-3184 .  
Abstract   PDF(pc) (90KB) ( 712 )
Conservation laws for partially conservative variable mass dynamical systems under symmetric infinitesimal transformations are determined. A generalization of Lagrange--d'Alembert's principle for a variable mass system in terms of asynchronous virtual variation is presented. The generalized Killing equations are obtained such that their solution yields the transformations and the associated conservation laws. An example illustrative of the theory is furnished at the end as well.
A Light-Cone QCD Inspired Effective Hamiltonian Model for Pseudoscalar and Scalar Mesons
TAO Jun, LI Lei, ZHOU Shan-Gui, WANG Shun-Jin
Chin. Phys. Lett. 2008, 25 (9): 3185-3187 .  
Abstract   PDF(pc) (106KB) ( 444 )

Considering the one-gluon exchange interaction and phenomenological quark confinement potential, an improved light-cone effective Hamiltonian for mesons and the corresponding radial mass eigen equations in angular momentum representation is obtained. Solving the J=0 eigen equations numerically and using a set of adjustable parameters, the obtained solutions for ground states and radial excited states can simultaneously describe both pseudoscalar and scalar flavour-off-diagonal mesons. Some radial excited states are also predicted and wait for experimental test. More results for the vector and axial vector mesons are expected.

Photons from Quark and Hadron Phases in Au + Au Collisions
LONG Jia-Li, HE Ze-Jun, , MA Yu-Gang, GUAN Na-Na
Chin. Phys. Lett. 2008, 25 (9): 3188-3191 .  
Abstract   PDF(pc) (191KB) ( 562 )
Based on a relativistic hydrodynamic model describing the evolution of the chemically equilibrating quark--gluon plasma system with finite baryon density in a 3+1-dimensional spacetime, we compute photons from the quark phase, hadronic phase and initial non-thermal contributions. It is found that due to the effects of the initial quark chemical potential, chemical equilibration and rapid expansion of the system, the photon yield of the quark--gluon plasma is strongly suppressed, and photons from hadronic matter and initial non-thermal contributions almost reproduce experimental data.
N ¯N S-Wave Elastic Cross Section and Possible Bound States in a Constituent Quark Model
PANG Hou-Rong, PING Jia-Lun WANG Fan
Chin. Phys. Lett. 2008, 25 (9): 3192-3195 .  
Abstract   PDF(pc) (162KB) ( 475 )
In the framework of a chiral constituent quark model, considering the contributions of π annihilation and one-gluon annihilation, the proton--antiproton s-wave elastic scattering cross section experimental data can be
reproduced by adjusting properly one-gluon annihilation coupling constant. After fixing the model parameters, we perform a dynamical calculation for all possible s-wave nucleon--antinucleon states. The results show that there is no s-wave bound state as indicated by a strong enhancement at threshold of p¯p in J/Ψ and B decay.
Charged Top-Pion Production Associated with a Gluon Jet at the LHC
WANG Xue-Lei, XU Wen-Na, XIAO Zhen-Jun
Chin. Phys. Lett. 2008, 25 (9): 3196-3199 .  
Abstract   PDF(pc) (153KB) ( 391 )

The charged top-pions have been predicted by the topcolour-assisted technicolour (TC2) model and the observation of the charged top-pions can be regarded as the robust evidence of the model. We study the charged top-pion and gluon associated production at the LHC, i.e., pp→gIIt+. The cross section of this process can reach tens of pb, even hundreds of pb, and there will be enough gIIt+ events produced at the LHC. Because the gIIt+ production is a flavour-changing (FC) process, the SM background can be greatly depressed. Furthermore, there exists an FC decay mode c¯b for the charged top-pions, and such decay mode can provide us with the typical signals to detect the charged top-pions. Therefore, it is hopeful to find the charged top-pions via the gIIt+ production at the LHC.

Rotational Bands of Some Neutron Deficient Odd-A Pt Isotopes in Particle-Triaxial-Rotor Model
WU Xian-Ming, LIU Yu-Xin
Chin. Phys. Lett. 2008, 25 (9): 3200-3203 .  
Abstract   PDF(pc) (139KB) ( 581 )
Theoretical calculations are performed for neutron deficient Pt isotopes 177Pt and 175,173,171Pt in the particle-triaxial-rotor model with variable moment of inertia. The obtained energy spectra agree with experimental data quite well. The calculated results indicate that all these nuclei are in triaxial rotation with 177Pt being in prolate and 175,173,171Pt in oblate. Several levels are predicted for the 13/2+ band in 169Pt.
Determination of Orientations in Deformed U--U Collisions at 0.52GeV/u
WU Ke-Jun, XIE Fei, ZHOU You, LIU Feng, XU Nu,
Chin. Phys. Lett. 2008, 25 (9): 3204-3207 .  
Abstract   PDF(pc) (228KB) ( 594 )
The ART model is applied to study the deformed UU collision at HIRFL-CSR energy area corresponding to the high baryon density region in the QCD phase diagram. The time evolution of central baryon (energy) densities in central collisions at Eb =0.52GeV/u shows that different orientation collisions will lead to different lifetimes of high density, especially tip--tip UU collisions which have an extend lifetime for the high density phase by almost a factor of 2 compared to the body--body orientation collisions. In order to pick out the interesting tip--tip like events from a mass of random orientation collisions, we study the relation between stopping power R and impact parameter b in different orientation collisions and find that it can enhance the purity of tip--tip like events when R increases. Therefore, the high density and long lifetime events can be effectively distinguished by R selection.
Total Fragmentation Cross Section of 158A GeV Lead Projectiles in Cu Target
Mukhtar Ahmed Rana, Shahid Manzoor
Chin. Phys. Lett. 2008, 25 (9): 3208-3211 .  
Abstract   PDF(pc) (200KB) ( 1038 )

Total fragmentation cross section for the reaction 158A Pb ions + Cu target is measured using the most sensitive track detector CR-39. Measured values are compared with calculations. Exposures of target-detector stack with 158A Pb projectiles are made at CERN-SPS beam facility. Results of calibration of CR-39 detector in a charge region (63≤Z≤83) are also reported, which can be used for high energy particle identification using CR-39 and in determination of partial charge changing cross sections. The charge resolution σZ achieved by this technique is about 0.2e. A systematic dependence of total fragmentation cross section on target properties is revealed and the corresponding results are presented.

Electronic Transport Properties of (7,0) Semiconducting Carbon Nanotube
SONG Jiu-Xu, YANG Yin-Tang, CHAI Chang-Chun, LIU Hong-Xia, DING Rui-Xue
Chin. Phys. Lett. 2008, 25 (9): 3212-3214 .  
Abstract   PDF(pc) (1393KB) ( 927 )
Electronic transport properties of a finite (7,0) carbon nanotube (CNT) coupled to Au (111) surfaces are investigated with a fully nonequilibrium Green's functions method combined with the density functional theory. The results show that the coupling effect between the CNT and Au electrode plays an important role in the transport properties, which leads0 to the formation of a high plateau in the transmission spectrum around Fermi energy. In addition, the current-voltage characteristic of the (7,0) CNT coupled to Au electrodes is different from an isolated (7,0) CNT.
A Novel Mirror for Cold Molecules with a Semi-Gaussian Beam
YIN Ya-Ling, ZHOU Qi, XIA Yong, YIN Jian-Ping
Chin. Phys. Lett. 2008, 25 (9): 3215-3218 .  
Abstract   PDF(pc) (367KB) ( 617 )
We propose a novel mirror for cold molecules with a blue-detuned semi-Gaussian beam and study the dynamic reflection process of cold molecules by Monte Carlo simulation. Our study shows that this mirror can realize a specular reflection of cold iodine molecular beam with a temperature of 30mK by a reflectivity of 58.2% when the semi-Gaussian laser power is 1.0kW. When a semi-Gaussian CO2 laser beam with a power of 5.8kW is used, the reflectivity of this mirror can reach about 100%.
Directly Trapping Atoms in a U-Shaped Magneto-Optical Trap Using a Mini Atom Chip
YAN Hui, , YANG Guo-Qing, , WANG Jin, ZHAN Ming-Sheng,
Chin. Phys. Lett. 2008, 25 (9): 3219-3222 .  
Abstract   PDF(pc) (1332KB) ( 706 )
We experimentally demonstrate the trapping of 85Rb atoms directly on a chip-size U-shaped magneto-optical trap (U-MOT). The trap includes a U-shaped wire on the chip, two bias magnetic field coils and laser beams. The capture volume of the U-MOT is theoretically calculated, and the trap is experimentally realized. With 2A current applied to the U-shaped wire and 2-Gauss horizontal bias field, more than 2×10^6 atoms are trapped. In contrast with an ordinary mirror-MOT, this U-MOT captures atoms directly from the background, thus the trap size is greatly reduced. Based on this mini trap scheme, it is possible to realize a chip-size atom trap array for quantum information processing.
Tightly Focusing of Circularly Polarized Vortex Beams through a Uniaxial Birefringent Crystal
RAO Lian-Zhou, WANG Zong-Chi, ZHENG Xiao-Xia
Chin. Phys. Lett. 2008, 25 (9): 3223-3226 .  
Abstract   PDF(pc) (1342KB) ( 686 )

Under the approximation of small birefringence, the properties of circularly polarized vortex beams tightly focused through a uniaxial birefringent crystal are studied. With the proper combination of the topological charge and the birefringence, the small focus, the small bottle beam and the inverse c-shaped intensity profile can be obtained. The effects of the focal shift and the Strehl ratio on the birefringence are analysed. A relation between angular momentum (included spin and orbital) and topological Pancharatnam charge is also presented.

Inverse Relaxation of Photoinduced Birefringence in a Liquid-Crystalline Azobenzene Side-Chain Polymer
PAN Xu, WANG Chang-Shun, ZHANG Xiao-Qiang
Chin. Phys. Lett. 2008, 25 (9): 3227-3230 .  
Abstract   PDF(pc) (227KB) ( 566 )
Photoinduced birefringence in a liquid-crystalline azobenzene side-chain polymer is investigated. It is observed that the birefringence does not show any decay but increases after switching off the pump light at room temperature. The magnitude of the birefringence relaxation is found to depend on the exposure dose of the pump light. A discussion about the mechanism of the inverse relaxation of birefringence is presented.
Single-Photon Emission at Liquid Nitrogen Temperature from a Single InAs/GaAs Quantum Dot
DOU Xiu-Ming, SUN Bao-Quan, CHANG Xiu-Ying, XIONG Yong-Hua, HUANG She-Song, NI Hai-Qiao, NIU Zhi-Chuan
Chin. Phys. Lett. 2008, 25 (9): 3231-3233 .  
Abstract   PDF(pc) (585KB) ( 845 )
We report on the single photon emission from single InAs/GaAs self-assembled Stranski--Krastanow quantum dots up to 80K under pulsed and continuous wave excitations. At temperature 80K, the second-order correlation function at zero time delay, g(2)(0), is measured to be 0.422 for pulsed excitation. At the same temperature under continuous wave excitation, the photon antibunching effect is observed. Thus, our experimental results demonstrate a promising potential application of self-assembled InAs/GaAs quantum dots in single photon emission at liquid nitrogen temperature.
Entangled Radiation through an Atomic Reservoir Controlled by Coherent Population Trapping
Li Qian, ZHONG Wen-Xue, HU Xiang-Ming
Chin. Phys. Lett. 2008, 25 (9): 3234-3237 .  
Abstract   PDF(pc) (120KB) ( 506 )
We show that it is possible to generate Einstein--Podolsky--Rosen (EPR) entangled radiation using an atomic reservoir controlled by coherent population trapping. A beam of three-level atoms is initially prepared in near-coherent population trapping (CPT) state and acts as a long-lived coherence-controlled reservoir. Four-wave mixing leads to amplification of cavity modes resonant with Rabi sidebands of the atomic dipole transitions. The cavity modes evolve into an EPR state, whose degree of entanglement is controlled by the intensities and the frequencies of the driving fields. This scheme uses the long-lived CPT coherence and is robust against spontaneous emission of the atomic beam. At the same time, this scheme is implemented in a one-step procedure, not in a two-step procedure as was required in Phys. Rev. Lett. 98(2007)240401.
Dicke-Narrowing Spectroscopy of Doubly Dressed Electromagnetically Induced Transparency and Singly Dressed Four-Wave-Mixing in a Confined Atomic System
LI Yuan-Yuan, BAI Jin-Tao, LI-Li, ZHANG Wei-Feng, LI Chang-Biao, NIEZhi-Qiang, GAN Chen-Li, ZHANG Yan-Peng
Chin. Phys. Lett. 2008, 25 (9): 3238-3241 .  
Abstract   PDF(pc) (179KB) ( 678 )

Dicke-narrowing effect appears both in doubly dressed electromagnetically induced transparency and singly dressed four-wave-mixing lines due to the contribution of slow atoms resulting from de-excited effects of atom-wall collision and transient behaviour of atoms in a confined system. A robust recipe for high resolution spectroscopy of electromagnetically induced transparency dressed by two fields and four-wave-mixing lines comparable with the cold atoms is achievable in a thin vapour cell in experiments.

Observation of Quantum Beating from Two Coupled Parametric Six-Wave Mixing Signals in Rb
ZHU Chang-Jun, HE Jun-Fang, ZHAI Xue-Jun, XUE Bing
Chin. Phys. Lett. 2008, 25 (9): 3242-3245 .  
Abstract   PDF(pc) (305KB) ( 437 )
Two processes of coupled difference-frequency axially phase-matched parametric six-wave mixing are carried out in Rb vapour by two-photon excitation using fs laser pulses, and parametric six-wave mixing signals in the infrared and near infrared regime are detected. The infrared parametric six-wave mixing signals are up-converted into the visible spectral range by sum-frequency mixing with the pump laser in a LiIO3 crystal. Moreover, quantum beating at 608cm-1, corresponding to the 7s-5d energy difference in Rb, is observed from the sum-frequency signal at 495nm. As a result, we obtain modulated light signals in the visible, near infrared and infrared spectral ranges, and study the interference between 7s and 5d states of Rb.
Gas Sensor Using a Robust Approach under Time Multiplexing Scheme with a Twin Laser Chip for Absorption and Reference
ZHANG Yong-Gang, GU Yi, Zhang Xiao-Jun, LI Ai-Zhen, TIAN Zhao-Bing
Chin. Phys. Lett. 2008, 25 (9): 3246-3249 .  
Abstract   PDF(pc) (661KB) ( 531 )
A tunable diode laser absorption spectroscopy nitrous oxide gas sensor at 2.1 micrometres using one antimonide twin laser chip and one InGaAs photodiode is demonstrated, in which time multiplexing techniques are adopted to acquiring both the absorption and reference signal in a robust fluctuation tolerable scheme. Electronics in analogue modality is developed to extracting absorption information and compensating for fluctuations, resulting in a direct analogue voltage output corresponding to the target gas concentration in real time. The performance of the gas sensor is evaluated experimentally, the validity and feasibility of this scheme is also discussed
A Single-Longitudinal-Mode Dual-Wavelength cw Tm,Ho:GdVO4 Microchip Laser
JU You-Lun, WANG Zhen-Guo, LI Yu-Feng, WANG Yue-Zhu
Chin. Phys. Lett. 2008, 25 (9): 3250-3252 .  
Abstract   PDF(pc) (743KB) ( 640 )
A liquid nitrogen cooled dual-wavelength Tm,Ho:GdVO4 microchip laser is reported. The output dual wavelengths are at 2038.9nm and 2050.1nm. At each wavelength, the laser has a single longitudinal mode. The threshold power is nearly 20mW and the slope efficiency is 18.7%. The single longitudinal mode output power reaches 98mW, and the ratio of power is about 60% (2038.9nm) and 40% 2050.1nm.
Realization of Optical Phase Locked Loop at 9.2GHz between Two Independent Diode Lasers
LI Lu-Ming, TANG Wen-Zhuo, HU Zhen-Yan, GUO Hong
Chin. Phys. Lett. 2008, 25 (9): 3253-3256 .  
Abstract   PDF(pc) (157KB) ( 698 )
The optical-phase-locked-loop (OPLL) at 9.2GHz between two independent narrow linewidth diode lasers is realized. Ultrabroad servo bandwidth at 4MHz is first achieved and it is guaranteed that the full spectral characteristics of the master laser can be transferred to the slave laser. The experimental results prove that the coherence between two lasers is about 99%. This offers a new method to study the interaction between lasers and atoms based on the ground hyperfine structure of caesium atoms.
Large Third-Order Optical Nonlinearity of a Novel Copper Phthalocyanine--Ferrocene Dyad
BIN Yue-Jing, XU Song, LI Zhong-Yu, HUANG Lei, ZHANG Zhi, ZHANG Fu-Shi
Chin. Phys. Lett. 2008, 25 (9): 3257-3259 .  
Abstract   PDF(pc) (167KB) ( 802 )
Third-order optical nonlinearity of a novel copper phthalocyanine--ferrocene dyad is measured by femtosecond forward degenerate four-wave mixing (DFWM) technique at 800nm. The second-order hyperpolarizability of the novel copper phthalocyanine--ferrocene dyad is measured to be 1.74×10-30 esu. This large and ultrafast third-order optical nonlinear response is mainly enhanced by the formation of intramolecular charge-transfer which can enhance the delocalized movements of the large π-electrons in the molecules.
Achievement of Narrow-Band CARS Signal by Manipulating Broad-band Laser Spectrum
ZHANG Shi-An, WANG Zu-Geng, SUN Zhen-Rong
Chin. Phys. Lett. 2008, 25 (9): 3260-3263 .  
Abstract   PDF(pc) (347KB) ( 431 )

We theoretically demonstrate the achievement of narrow-band coherent anti-Stokes Raman scattering (CARS) signal by manipulating broad-band probe spectrum. The narrowing of the CARS signal depends on the spectrum bandwidth of the probe beam, and thus high-resolution CARS signal for a complicated quantum system can be obtained by the simple spectrum manipulation. Furthermore, the energy-level diagram for the complicated quantum system can also be labelled by measuring the CARS signal at a given frequency.

Thermodynamics of Phase Transitions of a Kerr Nonlinear Blackbody
CHENG Ze
Chin. Phys. Lett. 2008, 25 (9): 3264-3267 .  
Abstract   PDF(pc) (232KB) ( 453 )

We study the thermodynamics of phase transitions of a blackbody whose interior is filled by a Kerr nonlinear crystal. There is a transition temperature Tc, above which the Kerr nonlinear blackbody is in the normal thermal radiation state, and below which it is in the squeezed thermal radiation state. At Tc, the Gibbs free energy of the two phases is continuous but the entropy density of the two phases is discontinuous. Hence, there is a jump in the entropy density and this leads to a latent heat density. The photon system undergoes a first-order phase transition from the normal to the squeezed thermal radiation state.

Laser Mode-Dependent Size of Plasma Zones Induced by Femtosecond Laser Pulses in Fused Silica
TANG Shan-Chun, JIANG Hong-Bing, LIU Yi, GONG Qi-Huang
Chin. Phys. Lett. 2008, 25 (9): 3268-3271 .  
Abstract   PDF(pc) (398KB) ( 405 )
We carry out the numerical simulations of femtosecond laser propagation with TEM00 mode, TEM10 mode and a beam combining both the modes in fused silica. It is found that the transverse size of plasma zones induced by laser pulses with the TEM10 mode is smaller than that induced by the TEM00 mode, while the longitudinal size is almost the same, and the saturated plasma density is higher. The transverse size, the longitudinal size and the ratio of the longitudinal to transverse size, for the beam combining both the modes, all could be reduced at the same time in comparison with the TEM00 mode under the same focusing conditions.
Red-Shift Conical Emission by Femtosecond Pulses at Low Input Power
LI Yue-Xun, JI Zhong-Gang, ZENG Zhi-Nan, LIU Jian-Sheng, GE Xiao-Chun, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2008, 25 (9): 3272-3275 .  
Abstract   PDF(pc) (2647KB) ( 394 )
Red-shift conical emission (CE) is observed by femtosecond laser pulse propagating in BK7 at a low input power (compared to those input powers for generation of blue-shift CE). With the increasing input power the blue-shift CE begins to appear whereas the red-shift CE ring (902nm in our experiment) disappears accompanied by the augment of the central white spot size synchronously. The disappearing of red-shift CE in our experiment is explained such that the increase of axial intensity is much higher than that of ring emission and the augment of the central white spot size with the increasing input laser power.
Enhancement of Second- and Third-Order Nonlinear Optical Susceptibilities in Magnetized Semiconductors
M. Singh, P. Aghamkar, S. Duhan
Chin. Phys. Lett. 2008, 25 (9): 3276-3279 .  
Abstract   PDF(pc) (1417KB) ( 538 )

Using electromagnetic treatment, an expression of effective nonlinear optical susceptibility χe e(2)e(3)E is obtained for III-V semiconducting crystals in an applied transverse dc magnetic field under off-resonant transition regime. The origin of nonlinear interaction lies in nonlinear polarization arising from the crystal properties such as piezoelectricity and electrostriction. Numerical estimates have been made by a representative n-InSb crystal at 77K duly irradiated by a pulsed 10.6-μm CO2 laser under off-resonant transition regime. Efforts are dedicated to optimizing doping level and externally applied dc magnetic field to achieve maximum χe(2) and χe(3). The results are found to be in good agreement with the available literature. The analysis shows that χe(2) and χe(3) can be significantly enhanced in doped III--V semiconductors by the proper selection of doping concentration and dc magnetic field, which confirms its potential as a candidate material for the fabrication of nonlinear optical devices.

Solitary Wave Evolution of Optical Planar Vortices in Self-Defocusing Photorefractive Media
GAN Xue-Tao, ZHANG Peng, LIU Sheng, XIAO Fa-Jun, ZHAO Jian-Lin
Chin. Phys. Lett. 2008, 25 (9): 3280-3283 .  
Abstract   PDF(pc) (2120KB) ( 460 )

Solitary wave evolution of optical planar vortices in isotropic self-defocusing photorefractive media is investigated in detail. We demonstrate that the formation of a planar vortex soliton intensively depends on the diameter and maximum intensity of the input vortex beam. The exact solutions of planar vortex solitons are obtained due to the Petviashvili iteration method. It is found that, with the increasing soliton maximum intensity, the soliton core will be gradually diminished to a minimum value.

Influence of Light Scattering on Transmission Spectra of Photonic Crystals of Anodized Alumina
HU Xing, LING Zhi-Yuan, CHEN Shuo-Shuo, HE Xin-Hua
Chin. Phys. Lett. 2008, 25 (9): 3284-3287 .  
Abstract   PDF(pc) (1000KB) ( 798 )
The light scattering is found to have a great influence on the transmission spectra of photonic crystal of anodic alumina. The incident light is diffracted by a regular array of branched channels or pores obeying the Bragg law. The intensity of transmission light decreases with the increasing etching time because of the increasing porosity or enlarging scatterers. The variation of intensity and widths of dips in transmission spectra of the porous alumina membrane versus the incidence angle shows the quite different characteristics from the other photonic crystal such as colloidal photonic crystal.
Write-Once Medium with Fe-Doped BiOx Thin Films for Blue Laser Recording
JIANG Zhi, GENG Yong-You, GU Dong-Hong
Chin. Phys. Lett. 2008, 25 (9): 3288-3291 .  
Abstract   PDF(pc) (662KB) ( 432 )
Fe:BiOx films are fabricated on K9 glass substrates by rf-magnetron sputtering of a BiFeO target under argon atmosphere with increasing sputtering power from 80 to 200W at room temperature. It is found that the thin films grown at the sputtering power of 160W can be formed at an appropriate deposition rate and have an improved surface morphology. The XPS result reveals that the films investigated are comprised of Bi, Fe and O elements. A typical XRD pattern shows that no phase transition occurs in the films up to 400°C. The results of the blue laser recording test demonstrate that the Fe:BiOx films have good writing sensitivity for blue laser beam (406.7nm) and good stability after reading 10000 times. The recording marks of 200nm or less are obtained. These results indicate that the introduction of Fe into BiOx films can reduce the mark size and improve the stability of the films.
Influence of Dielectric Loss on Quality Factors of Photonic Crystal Microcavity Modes
XIONG Zhi-Gang, LI Zhi-Yuan, ZHANG Dao-Zhong
Chin. Phys. Lett. 2008, 25 (9): 3292-3295 .  
Abstract   PDF(pc) (909KB) ( 553 )

We numerically investigate the quality factors of two-dimensional (2D) photonic crystal (PC) microcavities using an auxiliary differential equations (ADE) technique in the context of finite-difference time-domain (FDTD) method. The microcavities are formed by point defects in the air hole lattice hexagonally patterned in ZnO (zinc oxide) matrix. The quality factors of these microcavities are limited primarily by the absorption of the background dielectric. We show that the ratio between the quality factors of microcavities in lossy and lossless background dielectric depends on the overlap between the field of cavity modes and the absorbing background dielectric in addition to the magnitude of absorption. These results will be helpful when designing and optimizing photonic crystal microcavities formed in lossy medium.

Funnel-Shaped Arrays of Metal Nano-Cylinders for Nano-Focusing
ZHOU Xiu-Li, FU Yong-Qi, WANG Shi-Yong, PENG An-Jin, CAI Zhong-Heng
Chin. Phys. Lett. 2008, 25 (9): 3296-3299 .  
Abstract   PDF(pc) (1141KB) ( 540 )
We analyse funnel-shaped arrays of metal nanocylinders that can be potentially used as waveguides for nano-focusing of light. The proposed structures consist of Ag nanocylinders with gradually changed radii and discrete spacing arranged like side-view funnels with different angles. Finite-difference and time-domain simulations demonstrate that the proposed structures with different spacings and funnel angles have versatile light propagation characteristics. These structures can focus the incident Gaussian light beam (200nm at its full width at half maximum) into beam sizes of 10nm, 15nm, and 20nm, respectively, which corresponds to the transmission efficiencies of 38%, 40%, and 80%.
Laser Induced Damage Threshold at 355 and 1064nm of Ta2O5 Films of Different Phases
XU Cheng, LI Xiao, DONG Hong-Cheng, JIN Yun-Xia, HE Hong-Bo, SHAO Jian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2008, 25 (9): 3300-3303 .  
Abstract   PDF(pc) (1623KB) ( 574 )

Ta2O5 films are deposited on fused silica substrates by conventional electron beam evaporation method. By annealing at different temperatures, Ta2O5 films of amorphous, hexagonal and orthorhombic phases are obtained and confirmed by x-ray diffractometer (XRD) results. X-ray photoelectron spectroscopy (XPS) analysis shows that chemical composition of all the films is stoichiometry. It is found that the amorphous Ta2O5 film achieves the highest laser induced damage threshold (LIDT) either at 355 or 1064nm, followed by hexagonal phase and finally orthorhombic phase. The damage morphologies at 355 and 1064nm are different as the former shows a uniform fused area while the latter is centred on one or more defect points, which is induced by different damage mechanisms. The decrease of the LIDT at 1064nm is attributed to the increasing structural defect, while at 355nm is due to the combination effect of the increasing structural defect and decreasing band gap energy.

Distributed Measurement of Birefringence by P-OTDR Assisted with Piezoelectric Polarization Controller
YANG Shuang-Shou, WU Chong-Qing, LI Zheng-Yong, ZHANG Ren-Yuan, MENG Qing-Wen
Chin. Phys. Lett. 2008, 25 (9): 3304-3306 .  
Abstract   PDF(pc) (388KB) ( 794 )
We propose a new polarization sensitive optical time domain reflectometry (P-OTDR) setup assisted with a piezoelectric polarization controller (PPC). The input state of polarization can be changed by varying the voltage of PPC without any rotatable instrument, and only one optical receiver is used to detect the backward beam. We measure a single mode fibre and get the distribution of birefringence along the SMF.
Talbot Effect in Three Waveguide Arrays
LI Zhi, ZHOU Hai-Feng, YANG Jian-Yi, JIANG Xiao-Qing
Chin. Phys. Lett. 2008, 25 (9): 3307-3310 .  
Abstract   PDF(pc) (686KB) ( 465 )

By taking the coupling between the non-neighbourhood waveguides into account, the coupling characteristic of three waveguide arrays is analysed. The strong coupling equation of three waveguides is dealt with Laplace transform and LU decomposition. The general field evolution equation is obtained by inversion of the Laplace transform. The results show that the self-imaging conditions (Talbot effect) do not satisfy in general. The theoretical predictions are in good agreement with the BPM simulations.

A (2+1)-Dimensional Displacement Shallow Water Wave System
LIU Ping, LOU Sen-Yue,
Chin. Phys. Lett. 2008, 25 (9): 3311-3314 .  
Abstract   PDF(pc) (1385KB) ( 481 )
A new (2+1)-dimensional shallow water wave system, the (2+1)-dimensional displacement shallow water wave system (2DDSWWS), is constructed by applying variational principle of the analytic mechanics under the Lagrange coordinates. The general travelling wave solution is expressed as an elliptic integral. A special case is explicitly expressed by the Jacobi elliptic function which is a generalization of the solitary wave solution. Compared with some traditional (2+1)-dimensional shallow water wave systems such as the Kadomtsev--Petviashvili (KP) description under the Euler coordinates, the 2DDSWWS has some its own advantages. In addition, the KP equation can also be derived from the 2DDSWWS under the weak two-dimensional long-wave approximation.
Compressibility Effects in Turbulent Boundary Layers
CAO Yu-Hui, PEI Jie, CHEN Jun, SHE Zhen-Su,
Chin. Phys. Lett. 2008, 25 (9): 3315-3318 .  
Abstract   PDF(pc) (394KB) ( 442 )
Local cascade (LC) scheme and space-time correlations are used to study turbulent structures and their convection behaviour in the near-wall region of compressible boundary layers at Ma=0.8 and 1.3. The convection velocities of
fluctuating velocity components u (streamwise) and v (vertical) are investigated by statistically analysing scale-dependent ensembles of LC structures. The results suggest that u is convected with entropy perturbations while v with an isentropic process. An abnormal thin layer distinct from the conventional viscous sub-layer is discovered in the immediate vicinity of the wall (y+≤1) in supersonic flows. While in the region
1<y+<30, streamwise streaks dominate velocity, density and temperature fluctuations, the abnormal thin layer is dominated by spanwise streaks in vertical velocity and density fluctuations, where pressure and density fluctuations are strongly correlated. The LC scheme is proven to be effective in studying the nature of supersonic flows and compressibility effects on wall-bounded motions.
Temperature Dependence of Thermal Conductivity of Nanofluids
LI Yu-Hua, QU Wei, FENG Jian-Chao
Chin. Phys. Lett. 2008, 25 (9): 3319-3322 .  
Abstract   PDF(pc) (141KB) ( 2158 )
Mechanism of thermal conductivity of nanofluids is analysed and calculated, including Brownian motion effects, particle agglomeration and viscosity, together influenced by temperature. The results show that only Brownian motion as reported is not enough to describe the temperature dependence of the thermal conductivity of nanofluids. The change of particle agglomeration and viscosity with temperature are also important factors. As temperature increases, the reduction of the particle surface energy would decrease the agglomeration of nanoparticles, and the reduction of viscosity would improve the Brownian motion. The results agree well with the experimental data reported.
Observation of Periodic Multiplication and Chaotic Phenomena in Atmospheric Cold Plasma Jets
QI Bing, HUANG Jian-Jun, ZHANG Zhe-Huang, WANG De-Zhen
Chin. Phys. Lett. 2008, 25 (9): 3323-3325 .  
Abstract   PDF(pc) (376KB) ( 490 )
We investigate the temporal evolution of the current pulses from an ac He cold plasma jet at atmospheric pressure and with driving frequency in the range 14.76--15.30kHz. The driving frequency is used as the plasma system's bifurcation parameter in analogy with the evolution in which the current pulses undergoes multiplication and chaos. Such time-domain nonlinearity is important for controlling instabilities in atmospheric glow discharges. In addition, the observation can provide some data to support the simulation results reported previously [Appl. Phys. Lett. 90 (2007) 071501].
Diagnosis of Multiple Gases Separated from Transformer Oil Using Cavity-Enhanced Raman Spectroscopy
LI Xiao-Yun, XIA Yu-Xing, HUANG Ju-Ming, ZHAN Li
Chin. Phys. Lett. 2008, 25 (9): 3326-3329 .  
Abstract   PDF(pc) (165KB) ( 733 )
The Raman signal of gas molecules is very weak due to its small scattering cross section. Here, a near-confocal cavity-enhanced Raman detection system is demonstrated. In the cavity, a high power light of 9W is achieved by using a cw 200mW 532nm laser, which greatly enhances the detection sensitivity of gas species. A photomultiplier tube connected to a spectrometer is used as the detection system. The Raman spectra of the mixed gases separated from transformer oil has been observed. The relationship of absolute Raman intensity and gas pressure is also obtained. To our knowledge, this is the first Raman system to detect the gases separated from transformer oil.
Mono-Energetic Proton Beam Acceleration in Laser Foil-Plasma Interactions
YAN Xue-Qing, LIU Bi-Cheng, , HE Zhao-Han, SHENG Zheng-Ming, GUO Zhi-Yu, LU Yuan-Rong, FANG Jia-Xun, CHEN Jia-Erh
Chin. Phys. Lett. 2008, 25 (9): 3330-3333 .  
Abstract   PDF(pc) (1146KB) ( 480 )

Acceleration of ions from ultrathin foils irradiated by intense circularly polarized laser pulses is investigated using a one-dimensional particle-in-cell code. As a circularly polarized laser wave heats the electrons much less efficiently than the wave of linear polarization, the ion can be synchronously accelerated and bunched by the electrostatic field, thus a monoenergetic and high intensity proton beam can be generated.

Band Gap Energies and Refractive Indices of Epitaxial Pb1-xSrxTe Thin Films
WENG Bin-Bin, WU Hui-Zhen, SI Jian-Xiao, XU Tian-Ning
Chin. Phys. Lett. 2008, 25 (9): 3334-3337 .  
Abstract   PDF(pc) (159KB) ( 884 )
Pb1-xSrxTe thin films with different strontium (Sr) compositions are grown on BaF2(111) substrates by molecular beam epitaxy (MBE). Using high resolution x-ray diffraction (HRXRD), we obtain Pb1-xSrxTe latticeconstants, which vary in the range 6.462--6.492 AA. According to the Vegard law and HRXRD data, Sr compositions in Pb1-xSrxTe thin films range from 0.0--8.0%. The Pb1-xSrxTe refractive index dispersions are attained from infrared transmission spectrum characterized by Fourier transform infrared (FTIR) transmission spectroscopy. It is found that refractive index decreases while Sr content increases in Pb1-xSrxTe. We also simulate the Pb1-xSrxTe transmission spectra theoretically to obtain the optical band gap energies which range between 0.320eV and 0.449eV. The simulated results are in good agreement with the FTIR data. Finally, we determine the relation between Pb1-xSrxTe band gap energies and Sr compositions (Eg=0.320+0.510x-0.930x2 +184x3(eV)).
AFM Study on the Formation Mechanism and Microstructure of Ni Atomic Aggregates on Liquid Substrates
FANG Zheng-Nong, XIE Jian-Ping, FENG Yuan-Xin, ZHANG Chu-Hang, YANG Bo, YE Gao-Xiang
Chin. Phys. Lett. 2008, 25 (9): 3338-3341 .  
Abstract   PDF(pc) (3307KB) ( 500 )

We study the formation mechanism and microstructure of nickel (Ni) atomic aggregates on the silicone oil surfaces by atomic force microscopy (AFM). Initially, the deposited atoms nucleate and form the compact clusters on the liquid surfaces. Then they perform Brownian motion and adhere upon impact. Finally the branched aggregates are formed. The Ni aggregates exhibit granular structure. The mean size of the granularities in the aggregates is of the order of 10 nm and it decreases with the nominal film thickness. The experiment shows that the Ni aggregates perform a directional diffusion towards the sample edge. The interpretation for this phenomenon is presented.

Crystal Structure of β-La2Mo2O9 from First Principles Calculation
HOU Chun-Ju, ZHANG Xu, LIU Chang-Song, WANG Xian-Ping, FANGQian-Feng
Chin. Phys. Lett. 2008, 25 (9): 3342-3345 .  
Abstract   PDF(pc) (1493KB) ( 723 )
Arrangements of O ions in β-La2Mo2O9 are studied by first principles calculation with two different calculation schemes. All final structure configurations consist of MoO4-tetrahedra, MoO5-hexahedra, LaO8 and LaO7 polyhedra. Molybdenum polyhedra are isolated from each other, lanthanum polyhedra are connected together by sharing O ions. The occupancies of three crystallographic distinct O sites O(1), O(2) and O(3) are 100%, 91.7% and 25%, respectively, consistent with experiments. All configurations are related to each other by one of 12 symmetry operations of P213 space group, suggesting that the structure observed experimentally may be interpreted as a time and spatial average of these local or inherent structures.
Effect of Al Doping on Properties of SiC Films
SU Jian-Feng, YAO Ran, ZHONG Ze, FU Zhu-Xi
Chin. Phys. Lett. 2008, 25 (9): 3346-3349 .  
Abstract   PDF(pc) (6153KB) ( 466 )

Undoped and Al-doped 3C-SiC films are deposited on Si(100) substrates by low-pressure chemical vapour deposition. Effects of aluminium incorporation on crystallinity, strain stress, surface morphology and growth rate of SiC films have been investigated. The x-ray diffraction patterns and rocking curves indicate that the crystallinity is improved with aluminium doping. Raman scatting patterns also demonstrate that the strain stress in SiC films is released due to the incorporation of Al ions and the increase of film thickness. Furthermore, due to the catalysis of surface reaction which is induced by trimethylaluminium, the growth rate is increased greatly and the growth process varies from three-dimensional island-growth mode to step-flow growth mode.

Ultrahigh-Pressure Equation of State for Copper at 0K
WANG Xiao-Lu, GAO Xiang, MA Gui-Cun, YAN Jun, ZHANG Wen-Qing, LI Jia-Ming,
Chin. Phys. Lett. 2008, 25 (9): 3350-3352 .  
Abstract   PDF(pc) (131KB) ( 639 )

Based on the first-principles all-electron full-potential augmented-plane-wave plus local orbital method, an equation of state (EOS) at 0K for copper up to 10000GPa (108bar) is presented. Our recommended EOS is in good agreement with the available experimental data. Furthermore, the agreement between theoretical EOS of hcp and fcc lattices at extremely compressed condition sets the foundation of spherical atom models for high density and high temperate plasmas.

First-Principles Calculations of Electronic Structures of New III--V Semiconductors: BxGa1-xAs and TlxGa1-xAs alloys
ZHOU Jing, REN Xiao-Min, HUANG Yong-Qing, WANG Qi, HUANG Hui
Chin. Phys. Lett. 2008, 25 (9): 3353-3356 .  
Abstract   PDF(pc) (196KB) ( 527 )
We investigate the electronic structures of new semiconductor alloys BxGa1-xAs and TlxGa1-xAs, employing first-principles calculations within the density-functional theory and the generalized gradient approximation. The calculation results indicate that alloying a small Tl content with GaAs will produce larger modifications of the band structures compared to B. A careful investigation of the internal lattice structure relaxation shows that significant bond-length relaxations takes place in both the alloys, and it turns out that difference between the band-gap bowing behaviours for B and Tl stems from the different impact of atomic relaxation on the electronic structure. The relaxed structure yields electronic-structure results, which are in good agreement with the experimental data. Finally, a comparison of formation enthalpies
indicates that the production TlxGa1-xAs with Tl concentration of at least 8% is possible.

Observation of β-Relaxation in Sub-Tg Isothermally Annealed Al-Based Metallic Glasses
YANG Hong-Wang, TONG Wei-Ping, ZHAO Xiang, ZUO Liang, WANG Jian-Qiang
Chin. Phys. Lett. 2008, 25 (9): 3357-3359 .  
Abstract   PDF(pc) (126KB) ( 609 )
Al85Ni5Y8Co2 and Al85Ni5Y6Co2Fe2 metallic glasses are fabricated by melt spinning. A kink or a small exothermic peak is observed for both the samples isothermally annealed at sub-glass transition temperatures. Temperature modulated differential scanning calorimetry (TMDSC) data disapprove amorphous phase separation. The activation energies derived from Kissinger plots of the exothermic process on DSC curve around glass transition temperature are consistent with those of β-relaxation of metallic glasses.
Charge and Heat Transport in Polycrystalline Metallic Nanostructures
ZHANG Xing, TAKAHASHI Koji, FUJII Motoo
Chin. Phys. Lett. 2008, 25 (9): 3360-3363 .  
Abstract   PDF(pc) (705KB) ( 473 )

Metals are typically good conductors in which the abilities to transport charge and to transport heat can be related through the Wiedemann--Franz law. Here we report on an abnormal charge and heat transport in polycrystalline metallic nanostructures in which the ability to transport charge is weakened more obviously than that to transport heat. We attribute it to the influence of the internal grain boundaries and have formulated a novel relation to predict the thermal conductivity. The Wiedemann--Franz law is then modified to account for the influence of the grain boundaries on the charge and heat transport with the predictions now agreeing well with the measured results.

Adsorption and Reaction of CO on (100) Surface of SrTiO3 by Density Function Theory Calculation
YUN Jiang-Ni, ZHANG Zhi-Yong, ZHANG Fu-Chun
Chin. Phys. Lett. 2008, 25 (9): 3364-3367 .  
Abstract   PDF(pc) (4709KB) ( 718 )

Adsorption and reaction of CO on two possible terminations of SrTiO3 (100) surface are investigated by the first-principles calculation of plane wave ultrasoft pseudopotential based on the density function theory. The adsorption energy, Mulliken population analysis, density of states (DOS) and electronic density difference of CO on SrTiO3 (100) surface, which have never been investigated before as far as we know are performed. The calculated results reveal that the Ti-CO orientation is the most stable configuration and the adsorption energy (0.449eV) is quite small. CO molecules adsorb weakly on the SrTiO3 (100) surface, there is predominantly electrostatic attraction between CO and the surface rather than a chemical bonding mechanism.

First-Principles Calculations of Structures and Electronic Properties of Solid Pentaerythritol under Pressure
LU Lai-Yu, WEI Dong-Qing, CHEN Xiang-Rong, JI Guang-Fu
Chin. Phys. Lett. 2008, 25 (9): 3368-3371 .  
Abstract   PDF(pc) (164KB) ( 471 )
Structures and electronic properties of the pentaerythritol (PE) crystal under volume compression up to 0.85V0 are studied by E-V fitting method using density functional theory (DFT). The compression dependences of the cell volumes, lattice constants, and molecular geometries of solid PE are presented and discussed. It is found that the solid PE presents anisotropy along a- and c-axes, and the c axis is the most compressible. Decreasing anisotropy ratio (c/a) with elevating compression suggests an enhancement of the vdW interaction with increasing compression. The C--C and C--H bonds are significantly reduced under compression, which may be related to the sensitivity. The solid PE has indirect band gap (X-G) in the range of the researched compression and the band gap is decreased with compression.
Effect of Fe on Martensitic Transformation of NbRu High-Temperature Shape Memory Alloys: Experimental and Theoretical Study
TAN Chang-Long, TIAN Xiao-Hua, CAI Wei
Chin. Phys. Lett. 2008, 25 (9): 3372-3374 .  
Abstract   PDF(pc) (431KB) ( 415 )

Effect of Fe on the martensitic transformation of NbRu high-temperature shape memory alloys is investigated by the experiments and first-principles calculations. The results show that Fe is predicted to occupy Ru sites. The addition of Fe increases the stability of Nb50Ru50-xFex β phase, leading to the significant decrease of the β to β martensitic transformation temperature. In addition, the mechanism of the Fe alloying effect is explained on the basis of the electronic structure.

Variation of Different Characteristic Parameters of Pentacene/Poly(Methyl Methacrylate) Transistors under Electric Stress
DONG Gui-Fang, LIU Qing-Di, WANG Li-Duo, QIU Yong
Chin. Phys. Lett. 2008, 25 (9): 3375-3377 .  
Abstract   PDF(pc) (146KB) ( 441 )
By investigating the variation of different characteristic parameters of pentacene/poly(methyl methacrylate) transistors suffered from electric stress in an environment without O2, H2O and light, we deduce lifetimes of the transistors by different criterion parameters. Defined by the time for the parameters changing one half, the lifetime is different from the minimum of 7h (using on/off current ratio as the criterion parameter) to the maximum of 2.38×s108h (using transconductance as the criterion parameter). We also find that, under our experimental conditions, the main reason that affects the stabilities of the device is the increase of shallow traps formed in the organic semiconductors.
Difference of Oxide Hetero-structure Junctions with Semiconductor Electronic Devices
XIONG Guang-Cheng, CHEN Yuan-Sha, CHEN Li-Ping, LIAN Gui-Jun
Chin. Phys. Lett. 2008, 25 (9): 3378-3380 .  
Abstract   PDF(pc) (130KB) ( 449 )
Charge carrier injection is performed in Pr0.7Ca0.3MnO3 (PCMO) hetero-structure junctions, exhibiting the stability without electric fields and dramatic changes in both resistance and interface barriers, which are entirely different from behaviour of semiconductor devices. The disappearance and reversion of interface barriers suggest that the adjustable resistance switching of such hetero-structure oxide devices should associate with motion of charge carriers across interfaces. The results suggest that injected carriers should be still staying in devices and result in changes of properties, which lead to a carrier self-trapping and releasing picture in a strongly correlated electronic framework. Observations in PCMO and oxygen deficient CeO2-δ devices show that oxides as functional materials could be used in microelectronics with some novel properties, in which the interface is very important.
Relationship of Polaron Exchange with Ferromagnetic and Insulator--Metal Transitions in Doped Manganites
CHEN Li-Ping, MA Yu-Bin, SONG Xian-Feng, LIAN Gui-Jun, ZHANG Yan, XIONGGuang-Cheng
Chin. Phys. Lett. 2008, 25 (9): 3381-3384 .  
Abstract   PDF(pc) (161KB) ( 538 )

We report the experiment results and data analyses based on a polaron exchange model for La0.7Ca0.3MnO3 and Pr0.7(Sr1-xCax)0.3MnO3 epitaxial thin films. In the polaron exchange model with an energy balance condition, critical temperature of TC for stable ferromagnetic (FM) ordering should depend on &#8710; E as kBTC =E0 exp(-ΔE/kBTC), where &#8710; E denotes the potential barrier for the exchange polarons to overcome. Using the small polaron hopping model, the resistivity peak temperature TP is a function of the hopping energy Ehop. The dependence of TP on Ehop is similar to the dependence of TC on &#8710; E, which reveals that the polaron exchange relates to FM and insulator--metal transitions. The result indicates that the polaron exchange model is a simple way for describing the FM ordering, and is very helpful for understanding of complex doped manganites.

Influence of Width of Left Well on Intersubband Transitions in AlxGa1-x N/GaN Double Quantum Wells
LEI Shuang-Ying, SHEN Bo, ZHANG Guo-Yi
Chin. Phys. Lett. 2008, 25 (9): 3385-3388 .  
Abstract   PDF(pc) (151KB) ( 474 )

Influence of width of left well in AlxGa1-xN/GaN double quantum wells (DQWs) on absorption coefficients and wavelengths of the intersubband transitions (ISBTs) is investigated by solving the Schrödinger and Poisson equations self-consistently. When the width of left well is 1.79nm, three-energy-level DQWs are realized. The ISBT between the first odd and second odd order subbands (the 1odd-2odd ISBT) has a comparable absorption coefficient with the 1 odd-2even ISBT. Their wavelengths are located at 1.3 and 1.55μm, respectively. When the width of left well is 1.48nm, a four-energy-level DQWs is realized. The calculated results have a possible application to ultrafast two-colour optoelectronic devices operating within the optical communication wavelength range

Spin Filter Based on an Aharonov--Bohm Interferometer with Rashba Spin--Orbit Effect
FANG Ming, SUN Lian-Liang
Chin. Phys. Lett. 2008, 25 (9): 3389-3392 .  
Abstract   PDF(pc) (142KB) ( 591 )
We propose a spin filter based on both the quantum interference and the Rashba spin--orbit (RSO) effects. This spin filter consists of a Aharonov--Bohm (AB) interferometer with two quantum dots (QDs) inserted in its arms. The influences of a magnetic flux φ threading through the AB ring and the RSO interaction inside the two QDs are taken into account by using the nonequilibrium Green's function technique. Due to the existence of the RSO interaction, the electrons flowing through different arms of the ring will acquire a spin-dependent phase factor in the linewidth matrix elements. This phase factor, combined with the influence of the magnetic flux, will induce a spin-dependent electron transport through the device. Moreover, we show that by tuning the magnetic flux, the RSO strength and the inter-dot tunnelling coupling strength, a pure spin-up or spin-down conductance can be obtained when a spin-unpolarized current is injected from the external leads, which can be used to filter the electron spin.
Mechanism of NBTI Recovery under Negative Voltage Stress
CAO Yan-Rong, HU Shi-Gang, MA Xiao-Hua, HAO Yue
Chin. Phys. Lett. 2008, 25 (9): 3393-3396 .  
Abstract   PDF(pc) (402KB) ( 700 )
Recovery phenomenon is observed under negative gate voltage stress which is smaller than the previous degradation stress. We focus on the drain current to study the degradation and recovery of negative bias temperature instability (NBTI) with a real-time method. By this method, different recovery phenomena among different size devices are observed. Under negative recovery stress, the drain current gradually recovers for the large size devices and gets into recovery saturation when long recovery time is involved. For small-size devices, a step-like recovery of drain current is observed. The recovery of the drain current is mainly caused by the holes detrapping and tunnelling back to the channel surface which are trapped in oxide. The model of hole detrapping explains the recovery under negative voltage stress reasonably.
Magnetoresistance of Multiwalled Carbon Nanotube Yarns
SHENG Lei-Mei, GAO Wei, CAO Shi-Xun, ZHANG Jin-Cang
Chin. Phys. Lett. 2008, 25 (9): 3397-3399 .  
Abstract   PDF(pc) (2464KB) ( 635 )
We measure zero-field resistivity and magnetoresistance of multiwalled carbon nanotube yarns (CNTYs). The CNTYs are drawn from superaligned multiwalled carbon nanotube arrays synthesized by the low-pressure chemical vapour deposition method. The zero-field resistivity shows a logarithmic decrease from 2K to 300K. In the presence of a magnetic field applied perpendicular to the yarn axis, a pronounced negative magnetoresistance is observed. A magnetoresistance ratio of 22% is obtained. These behaviours can be explained by the weak localization effect.
Enhanced p-Type ZnO Films through Nitrogen and Argentum Codoping Grown by Ultrasonic Spray Pyrolysis
WANG Jing-Wei, BIAN Ji-Ming, LIANG Hong-Wei, SUN Jing-Chang, ZHAO Jian-Ze, HU Li-Zhong, LUO Ying-Min, DU Guo-Tong
Chin. Phys. Lett. 2008, 25 (9): 3400-3402 .  
Abstract   PDF(pc) (133KB) ( 629 )
The N--Ag codoped ZnO films are deposited on quartz glass substrates by ultrasonic spray pyrolysis technology. The results indicate that the p-type conductivity in ZnO films is greatly enhanced by the double acceptor codoping of N and Ag compared with that of Ag- and N-monodoped ZnO films, and the N--Ag codoped low-resistivity p-type ZnO films with the resistivity of 1.05Ω.cm, relatively high carrier concentration of 5.43×1017 cm-3, and Hall mobility of 10.09cm2V-1s-1 are obtained under optimized conditions. This achievement confirms that p-type ZnO with acceptable properties for optoelectronic applications could be realized by simultaneous codoping with two potential acceptors.
Superconductivity in Hole-Doped (Sr1-xKx)Fe2As2
CHEN Gen-Fu, LI Zheng, LI Gang, HU Wan-Zheng, DONG Jing, ZHOU Jun, ZHANG Xiao-Dong, ZHENG Ping, WANG Nan-Lin, LUO Jian-Lin
Chin. Phys. Lett. 2008, 25 (9): 3403-3405 .  
Abstract   PDF(pc) (584KB) ( 975 )
A series of layered (Sr1-xKx)Fe2As2 compounds with nominal x=0--0.40 are synthesized by solid state reaction method. Similar to other parent compounds of iron-based pnictide superconductors, pure SrFe2As2 shows a strong resistivity anomaly near 210 K, which was ascribed to the spin-density-wave instability. The anomaly temperature is much higher than those observed in LaOFeAs and BaFe2As2, the two prototype parent compounds with ZrCuSiAs- and ThCr2Si2-type structures. K-doping strongly suppresses this anomaly and induces superconductivity. Like in the case of K-doped BaFe2As2, sharp superconducting transitions at Tc38K is observed. We perform the Hall coefficient measurement, and confirm that the dominant carriers are hole-type. The carrier density is enhanced by a factor of 3 in comparison to F-doped LaOFeAs superconductor.
Anisotropic Applied Field Dependency of Two Successive Magnetic Transitions in LiCu2O2
ZHENG Ping, LUO Jian-Lin, WU Dong, SU Shao-Kui, LIU Guang-Tong, MAYong-Chang, CHEN Zhao-Jia
Chin. Phys. Lett. 2008, 25 (9): 3406-3409 .  
Abstract   PDF(pc) (1112KB) ( 476 )
The anisotropy of two successive transitions of the spin-ladder compound LiCu2O2 is studied by the specific heat (C) under magnetic fields with H//c and H // ab (written as Hc and Hab in the following) up to 14T. The peak of specific heat at 24.5K in zero field shifts to lower temperature when the field is increased and the magnitude of the peak is suppressed by the field. On the contrary, the peak of 22.5K shifts to higher temperature, especially at 14T. Its magnitude increases in the field of Hc, whereas it decreases in the field of Hab. We calculate the entropy change between 21K and 63K. The different influence of the spin ordering by fields of different direction is obtained. Our experimental results suggest a mixed state between the long range incommensurate helimagnetic ground state and the higher-T short-range dimer liquid state. The temperature range of mixed state is shrunk with the increasing field. Possible mechanism is discussed.
Nano-sized Domain Wall Pinning Effects in Dilute Cu-Doped Perovskite LaMn1-xCuxO3 Manganites
GAO Tian, CAO Shi-Xun, ZHANG Jin-Cang, YU Li-Ming, KANG Bao-Juan, YUAN Shu-Juan,
Chin. Phys. Lett. 2008, 25 (9): 3410-3413 .  
Abstract   PDF(pc) (297KB) ( 523 )

Magnetic properties of Cu-doped LaMn1-xCuxO3 (x=0.05--0.30) systems are carefully studied in the temperature range of 2--300K. A visible unexpected drop is observed in the ac susceptibility and the zero-field cooled dc magnetization curves for the dilute x≤0.10 near 100K, which depends on the measuring frequency and magnetic field. Measurements on frequency dependence of ac susceptibility, observation of magnetic relaxation, and the existence of critical field indicate that the anomaly can be attributed to the domain wall pinning effects. This is directly proven by the results of ball milled nano-sized powder counterparts compared with the bulk materials.

Amorphization Induced High Magneto-Caloric Effect of Gd55Al20Ni25 Ternary Alloy
DING Ding, XIA Lei, YU Zhong-Hua, DONG Yuan-Da
Chin. Phys. Lett. 2008, 25 (9): 3414-3417 .  
Abstract   PDF(pc) (1463KB) ( 856 )
We report the amorphization induced high magneto-caloric effect (MCE) of recently developed Gd55Al15Ni30 bulk metallic glass (BMG). The magnetic properties of the Gd55Al15Ni30 BMG are investigated in comparison with that of its crystalline counterpart. It is found that amorphization can increase the saturation magnetization and decrease the hysteresis of Gd55Al15Ni30 alloys, which indicate the possible enhancement of MCE. The magnetic entropy changes and the refrigerant capacity of the BMG as well as the crystalline samples is calculated directly from isothermal magnetic measurements. The results show the amorphization induced high MCE of the alloy and the excellent refrigerant efficiency of Gd55Al15Ni30 bulk metallic glass.
A Diffusion Model of Field-Induced Aggregation in Ferrofluid Film
FANG Wen-Xiao, HE Zhen-Hui, CHEN Di-Hu, ZHAO Yan-E
Chin. Phys. Lett. 2008, 25 (9): 3418-3421 .  
Abstract   PDF(pc) (154KB) ( 642 )

By introducing Arrhenius behaviour to the ferroparticles on the surface of the aggregated columnar structure in a diffusion model, equilibrium equations are set up. The solution of the equations shows that to keep the aggregated structures stable, a characteristic field is needed. The aggregation is enhanced by magnetic fields, yet suppressed as the temperature increases. Analysing the influence of the magnetic field on the interaction energy between the dipolar particles, we estimate the portion of the diffusing particles, and provide the agreeable ratio of the column radius over the centre-to-centre spacing between columns in a hexagonal columnar structure formed under a perpendicular magnetic field.

Influence of Surface Transition Layers on Phase Transformation and Pyroelectric Properties of Ferroelectric Thin Film
SUN Pu-Nan, LÜ, Tian-Quan, CHEN Hui, CAO Wen-Wu,
Chin. Phys. Lett. 2008, 25 (9): 3422-3425 .  
Abstract   PDF(pc) (170KB) ( 642 )
Taking into account surface transition layers (STLs), we study the phase transformation and pyroelectric properties of ferroelectric thin films by employing the transverse Ising model (TIM) in the framework of the mean field approximation. The distribution functions representing the intra-layer and inter-layer couplings between the two nearest neighbour pseudo-spins are introduced to characterize STLs. Compared with the results obtained by the traditional treatments for the thin films using only the single surface transition layer (SSL), it is shown that the STL model reflects a more realistic and comprehensive situation of films. The effects of various parameters on the phase transformation properties have shown that STL can make the Curie temperature of the film higher or lower than that of the corresponding bulk material, and the thickness of STL is a key factor influencing the film properties. For a film with definite thickness, there exists a critical STL thickness at which ferroelectricity will disappear when the intra-layer and inter-layer interactions are weak.
Laser Molecular Beam Epitaxy of Multilayer Heterostructure SrNb0.05Ti0.95O3/La0.9Sr0.1MnO3 in 10000 Unit-Cell Layers
HUANG Yan-Hong, HE Meng, TIAN Huan-Fang, ZHAO Kun, LÜ, Hui-Bin, JIN Kui-Juan, LI Jian-Qi, YANG Guo-Zhen
Chin. Phys. Lett. 2008, 25 (9): 3426-3428 .  
Abstract   PDF(pc) (1886KB) ( 337 )

Ten thousands of unit-cell multilayer heterosturctures, [SrNb0.05Ti0.95O3/La0.9Sr0.1MnO3]3 (SNTO/LSMO), have been epitaxial grown on SrTiO3 (001) substrates by laser molecular beam epitaxy. The monitor of in-situ reflection high-energy electron diffraction demonstrates that the heterosturctures are layer-by-layer epitaxial growth. Atomic force microscope observation indicates that the surface of the heterosturcture is atomically smooth. The measurements of cross-sectional low magnification and high-resolution transmission electron microscopy as well as the corresponding selected area electron diffraction reveal that the interfaces are of perfect orientation, and the epitaxial crystalline structure shows the orientation relation of SNTO(001)//LSMO(001), and SNTO[100]//LSMO[100].

Acoustic Imaging Frequency Dynamics of Ferroelectric Domains by Atomic Force Microscopy
ZHAO Kun-Yu, ZENG Hua-Rong, SONG Hong-Zhang, HUI Sen-Xing, LI Guo-Rongv, YIN Qing-Rui, Kiyoshi Shimamura, Chinna Venkadasamy Kannan, Encarnacion Antonia Garcia Villora, Shunji Takekawa, Kenji Kitamura
Chin. Phys. Lett. 2008, 25 (9): 3429-3432 .  
Abstract   PDF(pc) (8073KB) ( 420 )
We report the acoustic imaging frequency dynamics of ferroelectric domains by low-frequency acoustic probe microscopy based on the commercial atomic force microscopy. It is found that ferroelectric domain could be firstly visualized at lower frequency down to 0.5kHz by AFM-based acoustic microscopy. The frequency-dependent acoustic signal revealed a strong acoustic response in the frequency range from 7kHz to 10kHz, and reached maximum at 8.1kHz. The acoustic contrast mechanism can be ascribed to the different elastic response of ferroelectric microstructures to local elastic stress fields, which is induced by the acoustic wave transmitting in the sample when the piezoelectric transducer is vibrating and exciting acoustic wave under ac electric fields due to normal piezoelectric effects.
Influence of Ytterbia Content on Residual Stress and Microstructure of Y2O3--ZrO2 Thin Films Prepared by EB-PVD
XIAO Qi-Ling, SHAO Shu-Ying, HE Hong-Bo, SHAO Jian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2008, 25 (9): 3433-3435 .  
Abstract   PDF(pc) (131KB) ( 657 )

Y2O3 stabilized ZrO2 (YSZ) thin films with different Y2O3 molar contents (0, 3, 7, and 12mol%) are deposited on BK7 substrates by electron-beam evaporation technique. The effects of different Y2O3 contents on residual stresses and structures of YSZ thin films are studied. Residual stresses are investigated by means of two different techniques: the curvature measurement and x-ray diffraction method. It is found that the evolution of residual stresses of YSZ thin films by the two different methods is consistent. Residual stresses of films transform from compressive stress into tensile stress and the tensile stress increases monotonically with the increase of Y2O3 content. At the same time, the structures of these films change from the mixture of amorphous and monoclinic phases into high temperature cubic phase. The variations of residual stress correspond to the evolution of structures induced by adding of Y2O3 content.

Optoelectronic Properties for Armchair-Edge Graphene Nanoribbons
PENG Xin-Xiang, LIAO Wen-Hu, ZHOU Guang-Hui,
Chin. Phys. Lett. 2008, 25 (9): 3436-3439 .  
Abstract   PDF(pc) (170KB) ( 1434 )

We study theoretically the electronic and transport property for an armchair-edge graphene nanoribbon (GNR) with 12 and 11 transversal atomic lines, respectively. The GNR is irradiated under an external longitudinal polarized high-frequency electromagnetic field at low temperatures. Within the framework of linear response theory in the perturbative regime, we examine the joint density of states and the real conductance of the system. It is demonstrated that, by numerical examples, some new photon-assisted intersubband transitions over a certain range of field frequency exist with different selection rules from those of both zigzag-edge GNR and single-walled carbon nanotube. This opto-electron property dependence of armchair-edge GNR on field frequency may be used to detect the high-frequency electromagnetic irradiation.

Temperature Dependence of Photoluminescence from Single and Ensemble InAs/GaAs Quantum Dots
DOU Xiu-Ming, SUN Bao-Quan, XIONG Yong-Hua, HUANG She-Song, NIHai-Qiao, NIU Zhi-Chuan
Chin. Phys. Lett. 2008, 25 (9): 3440-3443 .  
Abstract   PDF(pc) (158KB) ( 885 )
We investigate the temperature dependence of photoluminescence from single and ensemble InAs/GaAs quantum dots systematically. As temperature increases, the exciton emission peak for single quantum dot shows broadening and redshift. For ensemble quantum dots, however, the exciton emission peak shows narrowing and fast redshift. We use a simple steady-state rate equation model to simulate the experimental data of photoluminescence spectra. It is confirmed that carrier--phonon scattering gives the broadening of the exciton emission peak in single quantum dots while the effects of carrier thermal escape and retrapping play an important role in the narrowing and fast redshift of the exciton emission peak in ensemble quantum dots.
Blue-to-Orange Tunable Luminescence from Europium Doped Yttrium--Silicon--Oxide--Nitride Phosphors
YANG Hu-Cheng, LI Cheng-Yu, PANG Ran, G. Lakshminarayana, ZHOU Shi-Feng, TENG Yu, QIU Jian-Rong
Chin. Phys. Lett. 2008, 25 (9): 3444-3447 .  
Abstract   PDF(pc) (335KB) ( 1661 )

Europium-doped yttrium--silicon--oxide--nitride phosphors are synthesized by carbothermal reduction and nitridation method. The crystal structure of the phosphors changed gradually from oxide Y2Si2O7 to nitride YSi3N5 state with increasing dosage of Si3N4 and carbon powder. The Y2Si2O7:Eu phosphor shows a blue emission at 465nm with 300nm excitation and a characteristic red emission of Eu3+ at 612nm with 230nm excitation. The YSi3N5:Eu phosphor shows a broad emission band centred at 595nm with some sharp peaks of Eu3+ with 325nm excitation. The absorption of the studied phosphors increases from 450 to 700nm with an increment in nitrogen content. Blue-to-orange tunable luminescence is observed with 390nm excitation.

Improved Light Extraction of GaN-based LEDs with Nano-roughened p-GaN Surfaces
GAO Hai-Yong, YAN Fa-Wang, FAN Zhong-Chao, LI Jin-Min, ZENG Yi-Ping, WANG Guo-Hong
Chin. Phys. Lett. 2008, 25 (9): 3448-3451 .  
Abstract   PDF(pc) (3382KB) ( 723 )
p-GaN surfaces are nano-roughened by plasma etching to improve the optical performance of GaN-based light emitting diodes (LEDs). The nano-roughened GaN present a relaxation of stress. The light extraction of the LEDs with
nano-roughened surfaces is greatly improved when compared with that of the conventional LEDs without nano-roughening. PL-mapping intensities of the nano-roughened LED epi-wafers for different roughening times present two to ten orders of enhancement. The light output powers are also higher for the nano-roughened LED devices. This improvement is attributed to that nano-roughened surfaces can provide photons multiple chances to escape from the LED surfaces.
Mo Back Contact for Flexible Polyimide Substrate Cu(In, Ga)Se2 Thin-Film Solar Cells
ZHANG Li, HE Qing, JIANG Wei-long, LIU Fang-fang, LI Chang-Jian, SUN Yun
Chin. Phys. Lett. 2008, 25 (9): 3452-3454 .  
Abstract   PDF(pc) (337KB) ( 2021 )
A dc magnetic sputtering process is applied to growth of a Mo back contact layer onto the flexible polyimide (PI) and rigid soda-lime glass (SLG) substrates. The structural and electrical properties of the Mo layer coated on the two kinds of substrates are investigated by x-ray diffraction (XRD) and Hall effect measurements. The results show that the Mo layer on SLG indicate more better crystal quality and lower resistivity than that on the PI sheets. In contrast to the SLG substrate, the resistivity of the Mo layer on PI is increased by the vacuum annealing process at the substrate temperature of 450°C under Se atmosphere, which is attributed to the cracked Mo layer induced by the mismatch of the coefficient of thermal expansion between PI and Mo material. The Cu(In,Ga)Se2 (CIGS) solar cells based on the PI and SLG substrates show the best conversion efficiencies of 8.16% and 10.98% (active area, 0.2cm2), respectively. The cell efficiency of flexible CIGS solar cells on PI is limited by its relatively lower fill factor caused by the Mo back contact.
Simulation of Phase-Change Random Access Memory with Ring-Type Contactor for Low Reset Current by Finite Element Modelling
GONG Yue-Feng, LING Yun, SONG Zhi-Tang, FENG Song-Lin
Chin. Phys. Lett. 2008, 25 (9): 3455-3458 .  
Abstract   PDF(pc) (429KB) ( 606 )
A three-dimensional finite element models for phase change random access memory (PCRAM) is established to simulate thermal and electrical behaviours during RESET operation. The RESET behaviours of the conventional structure (CS) and the ring-type contact in bottom electrode (RIB) are compared with each other. The simulation results indicate that the RIB cell has advantages of high heat efficiency for melting phase change material in cell, reduction of contact area and lower RESET current with maintaining good resistance contrast. The RESET current decreases from 1.26mA to 1.2mA and the heat consumption in GST material during programming increases from 12% to 37% in RIB structure. Thus the RIB structure PCRAM cell is suitable for future device with high heat efficiency and smaller RESET current
Glass Forming Ability of Metallic Glasses Evaluated by a New Criterion
CAO Qing-Ping, LI Jin-Fu, ZHOU Yao-He
Chin. Phys. Lett. 2008, 25 (9): 3459-3462 .  
Abstract   PDF(pc) (1172KB) ( 650 )
The glass-forming ability (GFA) of Cu--Zr binary alloys is evaluated using the existing criteria based on calorimetric parameters, and poor relations are found. Therefore, another parameter Trk defined as Tk/Tl, in which Tk is the Kauzmann temperature and Tl the equilibrium liquidus temperature, is proposed. It exhibits good agreements with the experimental data of the Cu--Zr system and other representative bulk metallic glass formers so long as classifying them into strong or fragile category. It is suggested that kinetic effects are irrelevantly incorporated in the GFA analysis in the previous work.
Probing Field Emission from Boron Carbide Nanowires
TIAN Ji-Fa, BAO Li-Hong, WANG Xing-Jun, HUI Chao, LIU Fei, LI Chen, SHEN Cheng-Min, WANG Zong-Li, GU Chang-Zhi, GAO Hong-Jun
Chin. Phys. Lett. 2008, 25 (9): 3463-3466 .  
Abstract   PDF(pc) (2589KB) ( 363 )
High density boron carbide nanowires are grown by an improved carbon thermal reduction technique. Transmission electron microscopy and electron energy lose spectroscopy of the sample show that the synthesized nanowires are B4C with good crystallization. The field emission measurement for an individual boron nanowire is performed by using a Pt tip installed in the focused ion beam system. A field emission current with enhancement factor of 106 is observed and the evolution process during emission is also carefully studied. Furthermore, a two-step field emission with stable emission current density is found from the high-density nanowire film. Our results together suggest that boron carbide nanowires are promising candidates for electron emission nanodevices.
Centimetre-Long Single Crystalline ZnO Fibres Prepared by Vapour Transportation
JI Zhen-Guo, HAO Fang, WANG Chao, XI Jun-Hua
Chin. Phys. Lett. 2008, 25 (9): 3467-3469 .  
Abstract   PDF(pc) (1002KB) ( 541 )
Centimetre-long ZnO fibres are synthesized by vapour transportation via thermal evaporation of ZnO powders. The growth process is carried out in a graphite crucible, in which ZnO powder is loaded as the source material, and a silicon wafer is positioned on the top of the crucible as the growth
substrate. During the growth process, the source temperature is kept at 800°C, and the substrate temperature is kept at 600°C. Typical growth time to obtain centimetre-long ZnO fibres is 5-10 hours. Scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) measurement results show that ZnO fibres are single crystalline with high crystalline quality and very low defects concentration.
Reversible Carriers Tunnelling in Asymmetric Coupled InGaN/GaN Quantum Wells
PEI Xiao-Jiang, GUO Li-Wei, WANG Yang, WANG Xiao-Hui, JIA Hai-Qiang, CHEN Hong, ZHOU Jun-Ming, WANG Li, Tamai N
Chin. Phys. Lett. 2008, 25 (9): 3470-3473 .  
Abstract   PDF(pc) (147KB) ( 480 )
Temperature-dependent photoluminescence (PL) and time resolved photoluminescence (TRPL) are performed to study the PL characteristics and carrier transfer mechanism in asymmetric coupled InGaN/GaN multiple quantum wells (AS-QWs). Our results reveal that abnormal carrier tunnelling from the wide quantum well (WQW) to the narrow quantum well (NQW) is
observed at temperature higher than about 100K, while a normal carrier tunnelling from the NQW to the WQW is observed at temperature lower than 100K. The reversible carrier tunnelling between the two QWs makes it possible to explore new types of temperature sensitive emission devices. It is shown that PL internal quantum efficiency (IQE) of the NQW is enhanced to about 46% due to the assistant of the abnormal carrier tunnelling.
Electrical Conductivity and Current--Voltage Characteristics of Individual Conducting Polymer PEDOT Nanowires
LONG Yun-Ze, DUVAIL Jean-Luc, CHEN Zhao-Jia, JIN Ai-Zi, GU Chang-Zhi
Chin. Phys. Lett. 2008, 25 (9): 3474-3477 .  
Abstract   PDF(pc) (1280KB) ( 1424 )
We report the current--voltage (I-V) characteristics and electrical conductivity of individual template-synthesized poly(3,4-ethylenedioxythiophene) (PEDOT)
nanowires (190±6 nm in diameter and σRT= 11.2±2,Ω-1cm-1) over a wide temperature range from 300 to 10K. With lowering temperature, the I-V characteristics become nonlinear around 50K, and a clear Coulomb gap-like structure appears in the differential conductance (dI/dV) spectra. The
temperature dependence of the resistance below 70K follows ln R T1/2, which can be interpreted as Efros--Shklovskii hopping conduction in the presence of a Coulomb gap. In addition, the influences of measurement methods such as the applied bias voltage magnitude, the two-probe and four-probe techniques used in the resistance measurements are also reported and discussed.
Radio-Frequency Characteristics of a Printed Rectangular Helix Slow-Wave Structure
FU Cheng-Fang, WEI Yan-Yu, WANG Wen-Xiang, GONG Yu-Bin
Chin. Phys. Lett. 2008, 25 (9): 3478-3481 .  
Abstract   PDF(pc) (413KB) ( 516 )
A new type of printed rectangular helix slow-wave structure (SWS) is investigated using the field-matching method and the electromagnetic integral equations at the boundaries. The radio-frequency characteristics including the dispersion equation and the coupling impedance for transverse antisymmetric (odd) modes of this structure are analysed. The numerical results agree well with the results obtained by the EM simulation software HFSS. It is shown that the dispersion of the rectangular helix circuit is weakened, the phase velocity is reduced after filling the dielectric materials in the rectangular helix SWS. As a planar slow-wave structure, this structure has potential applications in compact TWTs.
A New Method for Generating Hydrogen from Water
MENG Qing-Bo, LI Ke-Xin, LI Hong, FAN Yu-Zun, YU Zhe-Xun, LI Dong-Mei, LUO Yan-Hong, CHEN Li-Quan
Chin. Phys. Lett. 2008, 25 (9): 3482-3484 .  
Abstract   PDF(pc) (234KB) ( 478 )
A new method for generating hydrogen by the reaction of Al powder with water using iodine as additive is developed. I2 can penetrate through the surface oxide layer on aluminium to form AlI3. High solubility of AlI3 in water is benefited to activate Al surface. It is found that the production of hydrogen becomes significant above 60°C and obeys a logarithm rule. The pH value varies from 5 to 3 then back to 4.5 during the reaction, which is determined mainly by the kinetics of hydration reaction of AlI3 and the reaction of Al and HI produced spontaneously.
Fabrication and Optical Characterization of GaN-Based Nanopillar Light Emitting Diodes
ZHU Ji-Hong, ZHANG Shu-Ming, SUN Xian, ZHAO De-Gang, ZHU Jian-Jun, LIU Zong-Shun, JIANG De-Sheng, DUAN Li-Hong, WANG Hai, SHI Yong-Sheng, LIU Su-Ying, YANG Hui,
Chin. Phys. Lett. 2008, 25 (9): 3485-3488 .  
Abstract   PDF(pc) (1158KB) ( 910 )
InGaN/GaN-multiple-quantum-well-based light emitting diode (LED) nanopillar arrays with a diameter of approximately 200nm and a height of 700nm are fabricated by inductively coupled plasma etching using Ni self-assembled nanodots as etching mask. In comparison to the as-grown LED sample an enhancement by a factor of four of photoluminescence (PL) intensity is achieved after the fabrication of nanopillars, and a blue shift and a decrease of full width at half maximum of the PL peak are observed. The method of additional wet etching with different chemical solutions is used to remove the etch-induced damage. The result shows that the dilute HCl (HCl:H2O=1:1) treatment is the most effective. The PL intensity of nanopillar LEDs after such a treatment is about 3.5 times stronger than that before treatment.
Etch Damage Evaluation in Integrated Ferroelectric Capacitor Side Wall by Piezoresponse Force Microscopy
WANG Long-Hai, DAI Ying, DENG Zhao
Chin. Phys. Lett. 2008, 25 (9): 3489-3492 .  
Abstract   PDF(pc) (10982KB) ( 317 )
The etch damage in integrated ferroelectric capacitors side wall fabricated by the typical integrated process (TIP-FeCAP) and the innovated integrated process (IIP-FeCAP) are investigated by piezoresponse force microscopy (PFM). The IIP-FeCAP side wall exhibits fine and clear nanoscale domain images and the same piezoresponse signal as the thin film, and the domains can also be easily switched by an external voltage. In the TIP-FeCAP side wall, owing to the effect of etch damage, the very weak piezoresponse signal and some discrete domains can be observed, and the discrete domains cannot be switched by the applied 9V and -9V dc voltage. The PFM results reflect the etch damage in the integrated ferroelectric capacitors and also suggest that the PFM can be used as an efficacious tools to evaluate the etch damage at nanoscale and spatial variations.
Leader--Follower Consensus Problems of Multi-agent Systems with Noise Perturbation and Time Delays
SUN Yong-Zheng, RUAN Jiong
Chin. Phys. Lett. 2008, 25 (9): 3493-3495 .  
Abstract   PDF(pc) (139KB) ( 870 )
In light of the stability theory for stochastic differential delay equations, the leader--followerconsensus problem with noise perturbation and communication time delays is investigated. Communication among agents is modelled as a weighted directed graph and the weights are stochastically perturbed with white noise. It is analytically proven that the consensus could be achieved almost surely with the perturbation of noise and communication time delays. Furthermore, numerical examples are provided to illustrate the effectiveness of the theoretical results
Effect of Rolling Massage on Particle Moving Behaviour in Blood Vessels
YI Hou-Hui, FAN Li-Juan, YANG Xiao-Feng, CHEN Yan-Yan
Chin. Phys. Lett. 2008, 25 (9): 3496-3499 .  
Abstract   PDF(pc) (157KB) ( 533 )
The rolling massage manipulation is a classic Chinese massage, which is expected to eliminate many diseases. Here the effect of the rolling massage on the particle moving property in the blood vessels under the rolling massage manipulation is studied by the lattice Boltzmann simulation. The simulation results show that the particle moving behaviour depends on the rolling velocity, the distance between particle position and rolling position. The average values, including particle translational velocity and angular velocity, increase as the rolling velocity increases almost linearly. The result is helpful to understand the mechanism of the massage and develop the rolling techniques.
Spatial Pattern of an Epidemic Model with Cross-diffusion
LI Li, JIN Zhen, SUN Gui-Quan
Chin. Phys. Lett. 2008, 25 (9): 3500-3503 .  
Abstract   PDF(pc) (1843KB) ( 893 )
Pattern formation of a spatial epidemic model with both self- and cross-diffusion is investigated. From the Turing theory, it is well known that Turing pattern formation cannot occur for the equal self-diffusion coefficients. However, combined with cross-diffusion, the system will show emergence of isolated groups, i.e., stripe-like or spotted or coexistence of both, which we show by both mathematical analysis and numerical simulations. Our study shows that the interaction of self- and cross-diffusion can be considered as an important mechanism for the appearance of complex spatiotemporal dynamics in epidemic models
Spatial Games Based on Pursuing the Highest Average Payoff
YANG Han-Xin, WANG Bing-Hong, WANG Wen-Xu, RONG Zhi-Hai
Chin. Phys. Lett. 2008, 25 (9): 3504-3506 .  
Abstract   PDF(pc) (328KB) ( 403 )
We propose a strategy updating mechanism based on pursuing the highest average payoff to investigate the prisoner's dilemma game and the snowdrift game. We apply the new rule to investigate cooperative behaviours on regular, small-world, scale-free networks, and find spatial structure can maintain cooperation for the prisoner's dilemma game. In the snowdrift game, spatial structure can inhibit or promote cooperative behaviour which depends on payoff parameter. We further study cooperative behaviour on scale-free network in detail. Interestingly, non-monotonous behaviours observed on scale-free network with middle-degree individuals have the lowest cooperation level. We also find that large-degree individuals change their strategies more frequently for both games..
Order Parameter Hysteresis on the Complex Network
MA Pei-Jie, WANG Bing-Hong
Chin. Phys. Lett. 2008, 25 (9): 3507-3510 .  
Abstract   PDF(pc) (125KB) ( 430 )
Collective synchronization is investigated on the small-world network (NW model). The order parameter is introduced to measure the synchronization of phase. It is found that there are differences between the processes of synchronization and desynchronization. The dependence of order parameter on the coupling strength is shown like a hysteresis loop. The size of the loop demonstrates the non-monotonicity with the change of adding probability, and is relevant to the construction of the network. The area may be maximum, as the adding probability is equal to 0.4. This phenomenon indicates that the clusters in the network play an important role in the processes of synchronization and desynchronization
Characteristics of Wave--Particle Interaction in a Hydrogen Plasma
HE Hui-Yong, CHEN Liang-Xu, LI Jiang-Fan
Chin. Phys. Lett. 2008, 25 (9): 3511-3514 .  
Abstract   PDF(pc) (194KB) ( 466 )
We study the characteristics of cyclotron wave--particle interaction in a typical hydrogen plasma. The numerical calculations of minimum resonant energy Emin, resonant wave frequency ω$, and pitch angle diffusion coefficient Dαα for interactions between R-mode/L-mode and electrons/protons are presented. It is found that Emin decreases with ω for R-mode/electron, L-mode/proton and L-mode/electron interactions, but increase with ω for R-mode/proton interaction. It is shown that both R-mode and L-mode waves can efficiently scatter energetic (10keV~100keV) electrons and protons and cause precipitation loss at L=4, indicating that perhaps wave--particle interaction is a serious candidate for the ring current decay.
Pitch Angle Distribution Evolution of Energetic Electrons by Whistler-Mode Chorus
ZHENG Hui-Nan, SU Zhen-Peng, XIONG Ming
Chin. Phys. Lett. 2008, 25 (9): 3515-3518 .  
Abstract   PDF(pc) (532KB) ( 468 )
We develop a two-dimensional momentum and pitch angle code to solve the typical Fokker--Planck equation which governs wave--particle interaction in space plasmas. We carry out detailed calculations of momentum and pitch angle diffusion coefficients, and temporal evolution of pitch angle distribution for a band of chorus frequency distributed over a standard Gaussian spectrum particularly in the heart of the Earth's radiation belt L=4.5, where peaks of the electron phase space density are observed. We find that the Whistler-mode chorus can produce significant acceleration of electrons at large pitch angles, and can enhance the phase space density for energies of 0.5~1MeV by a factor of 10 or above after about 24h. This result can account for observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm.
113 articles