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Volume 21 Issue 3
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Original Articles
Generation of Two-Mode Nonclassical States via Dispersive Interaction in Trapped-Ion Cavity Quantum Electrodynamics
YANG Wen-Xing, ZHAN Zhi-Ming, LI Jia-Hua
Chin. Phys. Lett. 2004, 21 (3): 421-423 .  
Abstract   PDF(pc) (246KB) ( 662 )
We propose a simple method to generate a practical SU(2)-Schrödinger-cat state of a single trapped-ion vibration mode and the light field state, using the method based on a quantum system, which is composed of the one-dimensional trapped-ion motion and a single cavity field mode. Moreover, we discuss the methods proposed so far for the generation two-mode maximal quantum entangled state. The detection of such a state is also briefly discussed.

Thermal Entanglement in Superconducting Quantum-Interference-Device Qubits Coupled to Cavity Field
PAN Hai-Zhong, KUANG Le-Man
Chin. Phys. Lett. 2004, 21 (3): 424-427 .  
Abstract   PDF(pc) (281KB) ( 400 )
We investigate thermal entanglement in a superconducting-quantum-interference-device qubit coupled to a cavity field. We show that the entanglement can be manipulated by varying temperature and an effective controlling parameter B which depends on the external field and characteristic parameters of the system. We find that there exists a critical value of the controlling parameter Bc. Under a fixed temperature, increasing B can increase entanglement in the regime of B < Bc, while the entanglement decreases with increasing B in the regime of B > Bc.

Quasinormal Modes in Three-Dimensional Time-Dependent Anti-de-Sitter Spacetime
SHEN Zai-Xiong, WANG Bin, SU Ru-Keng,
Chin. Phys. Lett. 2004, 21 (3): 428-431 .  
Abstract   PDF(pc) (508KB) ( 421 )
We study the massless scalar wave propagation in the time dependent Banados Teitelboim-Zanelli black hole background. It is shown that in the quasinormal ringing, both the decay and the oscillation timescales are modified in the time-dependent background.
Entropy of the Schwarzschild Black Hole in the Painlevé and the Lemaitre Coordinates
JING Ji-Liang, CHEN Song-Bai
Chin. Phys. Lett. 2004, 21 (3): 432-434 .  
Abstract   PDF(pc) (201KB) ( 405 )
In the Painlevé and the Lemaitre coordinates, the statistical-mechanical entropies of the Schwarzschild black hole arising from the quantum scalar field are investigated by using the ’t Hooft’s brick wall model. At first sight, it seems that the results would be different from that in the standard Schwarzschild coordinate since both the Painlevé and the Lemaitre spacetimes do not possess the event horizon obviously. However, we prove that the entropies in these coordinates are exactly equivalent to that in the Schwarzschild coordinate.

Responses of a Noisy Excitable System to External Signals with Different Periods
Chin. Phys. Lett. 2004, 21 (3): 435-438 .  
Abstract   PDF(pc) (488KB) ( 435 )
The behaviour of an excitable system under Gaussian white noise and external periodic forcing is systematically studied. In a large range of noise intensity, the n:1 phase locking patterns are obtained for certain ranges of the input periods, where n input periods give one spike. In the phase locking regimes, the system presents low noise-to-signal ratios and shows better regularities. Out of the regimes the system behaves less regularly and the relations between the noise-to-signal ratio and the noise intensity exhibit typical stochastic resonance phenomena. At a higher noise level, the system shows the characteristic behaviour of the noise.

Hopf Bifurcation in a Nonlinear Wave System
HE Kai-Fen
Chin. Phys. Lett. 2004, 21 (3): 439-442 .  
Abstract   PDF(pc) (560KB) ( 468 )
Bifurcation behaviour of a nonlinear wave system is studied by utilizing the data in solving the nonlinear wave equation. By shifting to the steady wave frame and taking into account the Doppler effect, the nonlinear wave can be transformed into a set of coupled oscillators with its (stable or unstable) steady wave as the fixed point. It is found that in the chosen parameter regime, both mode amplitudes and phases of the wave can bifurcate to limit cycles attributed to the Hopf instability. It is emphasized that the investigation is carried out in a pure nonlinear wave framework, and the method can be used for further exploration of the routes to turbulence.

Soliton Collision in a Ferromagnetic Spin Chain Driven by a Magnetic Field
LI Zai-Dong, LI Lu, LIANG Jiu-Qing
Chin. Phys. Lett. 2004, 21 (3): 443-446 .  
Abstract   PDF(pc) (219KB) ( 498 )
By employing an inverse-scattering transformation, the exact solution of an N-soliton train in the spin chain with a time-dependent magnetic field is derived. As a special case the one-soliton solution (N = 1) exhibits explicitly the spin precession around the magnetic field and periodic shape-variation induced by the time varying field as well. In terms of the general solution, the inelastic two-soliton collision is analysed. The inelastic collision, by which we mean the soliton shape-change before and after collision, appears generally due to the time varying field.

Can a Single-Wall Carbon Nanotube be an X-Ray Waveguide?
SUN Yu-Jie, CHENG Yao, WANG Feng, LI Jia-Ming,
Chin. Phys. Lett. 2004, 21 (3): 447-449 .  
Abstract   PDF(pc) (428KB) ( 532 )
We study the transport efficiency for x-rays of single-wall carbon nanotubes (SWCNTs) in theory. Three effects, i.e. refraction, absorption and x-ray tunnelling loss, are considered. Our calculation shows that the SWCNT cannot be an x-ray waveguide due to the large x-ray tunnelling loss. If the tunnelling loss can be reduced effectively, a nanotube could be a waveguide.

Nuclear Effects in Polarized Proton--Deuteron Drell-Yan Processes
DUAN Chun-Gui, , SHI Li-Jie, SHEN Peng-Nian, LI Guang-Lie,
Chin. Phys. Lett. 2004, 21 (3): 450-452 .  
Abstract   PDF(pc) (259KB) ( 386 )
The longitudinally polarized Drell-Yan process is one of the most powerful tools to probe the structure of hadrons. By means of the recent formalism of the polarized proton-deuteron (pd) Drell-Yan, we calculate the ratio of the proton-deuteron Drell-Yan cross section to the proton-proton (pp) one Δ\σpd/2Δσpp in the polarized case. The theoretical results can be compared with future experimental data to confirm the nuclear effect due to the 6-quark cluster in deuteron.
Properties of the Alpha Decay Chain Nuclei of 310126, 292120 and 298114
WANG Ting-Tai, JIANG Wei-Zhou, ZHANG Wei, WANG Kun, ZHU Zhi-Yuan
Chin. Phys. Lett. 2004, 21 (3): 453-456 .  
Abstract   PDF(pc) (433KB) ( 449 )
The properties of the α decay nuclei of 310126, 292120 and 298114 are investigated in the deformed relativistic mean-field model. The nuclear properties are investigated with the TMA and NL-Z2 parameter sets, and compared with Moller’s result [At. Data Nucl. Data Tables 59 (1995) 185]. The results show that the α decay energy increases systematically with the increasing proton number. Meanwhile, the α decay energy has a minimum value at the point of shell closure. It is also found that of the three nuclei, 292120 is the more likely to be the next doubly magic nucleus.

P-Wave Nuclear Halos in 8B and 11Be
LIU Zu-Hua, BAO Jing-Dong,
Chin. Phys. Lett. 2004, 21 (3): 457-460 .  
Abstract   PDF(pc) (346KB) ( 464 )
We use a procedure to extract valuable information regarding the p-wave halos in 8B and 11Be from the measured nuclear asymptotic normalization coefficients. With this procedure, we evaluate the probabilities of valence particle being outside the binding potential, which are 0.31±0.03 for the 8B ground state and 0.59±0.06 for the 11Be first excited state. More than 50% probability outside the binding potential means that the 11Be first excited state has a typical p-wave neutron halo. The rms radii are obtained to be 3.9±0.2 fm for the valence proton in the 8B ground state and to be 6.5±0.3 fm for the valence neutron in the 11Be first excited state. The probabilities of the valence particle being in the non-classical region are extracted to be 0.41±0.04 and 0.46±0.05 for the 8B ground state and the 11Be first excited state, respectively. The results demonstrate that although hindered by the effects of Coulomb and/or centrifugal barriers, their valence particle wavefunction still penetrates substantially into the classically forbidden region.
Lifetimes of Excited Levels in 131Ce
LI Guang-Sheng, MENG Rui, ZHU Li-Hua, ZHANG Zhen-Long, WANG Yue, WANG Zhi-Min, WEN Shu-Xian, LU Jing-Bin, ZHAO Guang-Yi, LI Xian-Feng, WEN Li-Jun, ZHENG Yong-Nan, ZHENG Yong, LIU Yun-Zuo, YUAN Guan-Jun, YANG Chun-Xiang
Chin. Phys. Lett. 2004, 21 (3): 461-463 .  
Abstract   PDF(pc) (351KB) ( 407 )
The fusion--evaporation reaction 116Sn (19F, p3n) 131Ce at projectile energy of 95 MeV is used to populate high spin states in 131Ce. The de-exciting γ-rays are detected in γ-γ coincidence measurement with Compton-suppressed BGO-HPGe detectors. Level lifetimes of 131Ce were determined by using the Doppler shift attenuation method. The experimental results indicate that collectivity of 131Ce is reduced relative to that of 130Ce and it follows that deformation decreases with increase of the neutron number on the basis of systematic comparison of transition quadrupole moments for the light cerium isotopes.

A Proposed Reaction Channel for the Synthesis of the Superheavy Nucleus Z = 109
WANG Kun, MA Yu-Gang, MA Guo-Liang, WEI Yi-Bin, CAI Xiang-Zhou, CHEN Jin-Gen, GUO Wei, ZHONG Chen, SHEN Wen-Qing,
Chin. Phys. Lett. 2004, 21 (3): 464-467 .  
Abstract   PDF(pc) (317KB) ( 396 )
We apply a statistical-evaporation model (HIVAP) to calculate the cross sections of superheavy elements, mainly in relation to actinide targets, and compare with some available experimental data. A reaction channel 30Si + 243Am is proposed for the synthesis of the element Z = 109 and the cross section is estimated.
Carrier-Envelope Phase-Dependent Effect on Photoelectron Angular Distribution in Single-Cycle Laser Pulses
ZHANG Jie, ZHANG Jing-Tao, SUN Zhen-Rong, XU Zhi-Zhan,
Chin. Phys. Lett. 2004, 21 (3): 468-471 .  
Abstract   PDF(pc) (328KB) ( 526 )
Using a nonperturbative scattering theory, we study the photoelectron angular distributions (PADs) of Kr atoms irradiated by an infinite sequence of intense single-cycle pulses of circular polarization. We demonstrate the inversion asymmetry of PADs and the dependence of PADs on the carrier-envelope phase of the single-cycle pulses. The inversion asymmetry is caused by the interference between transition channels where the different channels are characterized by different combinations of absorbed-photon numbers in the ionization process. Our results provide a possible method to determine the value of carrier-envelope phase by the detected PADs.
Differential Cross Sections for Elastic Scattering of Low-Energy Electrons by O2
LIU Wen-Wang, ZHOU Ya-Jun, WANG Zhi-Gang
Chin. Phys. Lett. 2004, 21 (3): 472-473 .  
Abstract   PDF(pc) (293KB) ( 678 )
Differential cross sections for the elastic scattering of electrons by oxygen molecule are calculated for selected impact energies 7 eV and 9 eV. The results are compared with other theoretical results and experimental data. The present results are obtained by the momentum space optical potential method. This method take the polarization of target states into account, which is very important for the scattering problem, particularly at low energies.

Total Cross Sections for Electron Scattering from the Isoelectronic (Z = 14) Molecules (C2H2, CO, HCN and N2) at 100-5000 eV
SHI De-Heng, , ZHU Zun-Lue, SUN Jin-Feng, YANG Xiang-Dong, LIU Yu-Fang, ZHAO Ye
Chin. Phys. Lett. 2004, 21 (3): 474-477 .  
Abstract   PDF(pc) (394KB) ( 533 )
A complex optical model potential correlated by the concept of bonded atom, which considers the overlapping effect of electron clouds between the two atoms in a molecule, is employed to calculate the total cross sections for electron scattering from the isoelectronic (Z = 14) molecules (C2H2, CO, HCN, and N2) at 100-5000 eV using the additivity rule at the Hartree-Fock level. The difference between the bonded atom and the free one is that the overlapping effect of electron clouds of bonded atoms in molecules is considered. The quantitative molecular total cross section results are compared with the experimental data and with other calculations available and good agreement is obtained above 100 eV. It is shown that the additivity rule along with the complex optical model potential considering the overlapping effect of electron clouds can give results better than when uncorrelated by it. The correlating calculations are much closer to the experiments than the spherical-complex-optical-potential results in the lower energy region [Phys. Rev. A 45 (1992) 202]. Therefore, considering the overlapping effect of electron clouds in the complex optical potential could be helpful for the better accuracy of the total cross section calculations of electron scattering from molecules.
Absolute Generalized-Oscillator-Strength Measurement of C 1 s Preionization-Edge Electronic Excitations of C2F6
FAN Xiao-Wei, LIAO Tian-He, ZHANG Xian-Zhou, GAO Jin-Hui, WEI Jian-Yu, K. T. Leung
Chin. Phys. Lett. 2004, 21 (3): 478-480 .  
Abstract   PDF(pc) (339KB) ( 735 )
Absolute generalized oscillator strengths (GOSs) for the C 1 s preionization-edge transitions at 295.4 eV and 297.7 eV in perfluoroethane have been determined as functions of energy loss and momentum transfer (K) at impact energy of 2.5 keV for the first time. The corresponding GOS profiles have been found to have the characteristic dipole-dominated shapes with a strong maximum at K = 0. The spectral features can be interpreted in terms of transitions terminating at the σ* (C-F) molecular orbital.

Anisotropic Energetic Ion Emission from Explosion of Intense Laser Irradiated Argon Clusters in a Jet
LI Shao-Hui, WANG Cheng, LIU Jian-Sheng, WANG Xiang-Xin, ZHU Pin-Pin, LI Ru-Xin, NI Guo-Quan, XU Zhi-Zhan
Chin. Phys. Lett. 2004, 21 (3): 481-484 .  
Abstract   PDF(pc) (388KB) ( 386 )
The interaction of an intense femtosecond laser field (~ 1016W/cm2) with argon clusters in a dense jet has been studied by measuring the energy and angle distributions of emitted ions. A directional anisotropy in the ion explosion energies is observed. The experimental results indicate that the average ion energies are up to 40% in the detection direction parallel to the laser polarization higher than that perpendicular to it. The measured ion yield increases about 80%, correspondingly. The findings are interpreted by charge-dependent ion acceleration and explosion of elliptic microplasma spheres.
Thin-Film Enhanced Goos-Hänchen Shift in Total Internal Reflection
LI Chun-Fang, YANG Xiao-Yan
Chin. Phys. Lett. 2004, 21 (3): 485-488 .  
Abstract   PDF(pc) (391KB) ( 500 )
It is reported that the Goos-Hänchen (GH) shift of both TE and TM light beams totally reflected from a dielectric interface can be greatly enhanced by a dielectric thin film without changing the property of total internal reflection. Numerical simulations confirm the theoretical analysis and show that the enhanced GH shift can be as large as the width of the beam for beam's width up to 820 times of the wavelength. This may stimulate investigations in other areas of physics and may lead to interesting applications in optical devices. The enhancement of the GH shift is accompanied by the enhancement of the intensity of the decaying field in the optically thin medium and of the propagating field inside the film.

Effect of Background Noise on the Photon Statistics of Triggered Single Molecules
XIAO Lian-Tuan, ZHAO Yan-Ting, HUANG Tao, ZHAO Jian-Ming, YIN Wang-Bao, JIA Suo-Tang
Chin. Phys. Lett. 2004, 21 (3): 489-492 .  
Abstract   PDF(pc) (311KB) ( 456 )
We theoretically derive exact expressions for Mandel’s Q parameter of the triggered single molecular source, which is inferred from the probabilities PRS(n) using the record of each photon detection event based on Hanbury Brown and Twiss detection. The real triggered source is recognized as an ideal single photon source with a Poissonian statistics background. How to decrease the background and to increase the efficiency are discussed. It is established that the sub-Poissonian statistics formation can be determined by comparing the measured QRS of the real single triggered molecular with QC of the Poissonian source containing the same mean photons. By this method, we also give an efficient way to measure signal-to-background ratios of triggered single photons.

Laterally Confined Modes in Wet-Etched, Metal-Coated, Quantum-Dot-Inserted Pillar Microcavities
ZHANG Hao, ZHENG Hou-Zhi, ZHANG Ji-Dong, XU Ping, TAN Ping-Heng, YANG Fu-Hua, ZENG Yi-Ping
Chin. Phys. Lett. 2004, 21 (3): 493-496 .  
Abstract   PDF(pc) (468KB) ( 641 )
We report the fabrication and the measurement of microcavities whose optical eigenmodes were discrete and were well predicted by using the model of the photonic dot with perfectly reflected sidewalls. These microcavities consisted of the semiconductor pillar fabricated by the simple wet-etched process and successive metal coating. Angle-resolved photoluminescence spectra demonstrate the characteristic emission of the corresponding eigenmodes, its pattern revealed by varying both polar (θ) and azimuthal (Ф) angles. It is shown that the metal-coated sidewalls can provide an efficient way to suppress the emission due to the leaking modes in these pillar microcavities.
Scheme for Generation of Entanglement among Bimodal Cavities
SONG Xin-Guo, FENG Xun-Li
Chin. Phys. Lett. 2004, 21 (3): 497-499 .  
Abstract   PDF(pc) (219KB) ( 618 )
We present a scheme for generation of an entangled state in many spatially separated bimodal cavity modes via cavity quantum
electrodynamics. A V-type three-level atom, initially prepared in a coherent superposition of its excited states, successively passes through both the bimodal cavities. If the atom is measured in its ground state after leaving the last cavity, an entangled state of many cavity modes can be generated. The conditions to generate the maximally entangled state with unity probability are worked out.

Switchable Dual-Wavelength Mode-Locked Er-Doped Fibre Laser Using a Bragg Grating in Polarization-Maintaining Fibre
FENG Xin-Huan, LIU Yan-Ge, SUN Lei, XIONG Ling-Yun, LI-Yao, YUAN Shu-Zhong, KAI Gui-Yun, DONG Xiao-Yi
Chin. Phys. Lett. 2004, 21 (3): 500-502 .  
Abstract   PDF(pc) (353KB) ( 631 )
A simple actively mode-locked fibre ring laser is proposed and successfully demonstrated to generate switchable dual-wavelength picosecond pulses using a Bragg grating in a polarization-maintaining fibre. The wavelength spacing specified by the grating is only 0.52 nm. The proposed laser can be made to operate in stable dual-wavelength or switch between wavelengths at room temperature, only by simple adjustment of a polarization controller.

A Simple Calculation Approach for the Second-Harmonic Sound Beam Generated by an Arbitrary Distribution Source
Chin. Phys. Lett. 2004, 21 (3): 503-506 .  
Abstract   PDF(pc) (259KB) ( 463 )
We present a simple calculation approach for the fundamental and second-harmonic sound beams with an arbitrary distribution source in the quasilinear approximation. The analysis is based on the assumption that the source function with an arbitrary geometry and distribution is expanded into the sum of a set of two-dimensional Gaussian functions. The two- and five-dimensional integral solutions for the fundamental and second-harmonic fields are, respectively, reduced in terms of Gaussian functions and simple one-dimensional integrals. The numerical evaluation of field distributions is then greatly simplified.

Effect of the Initial Laser Phase on the Interaction Between Relativistic Electron and Ultra-Intense Laser Field in a Strong Uniform Magnetic Field
HE Xin-Kui, SHUAI Bin, GE Xiao-Chun, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2004, 21 (3): 507-510 .  
Abstract   PDF(pc) (646KB) ( 395 )
We investigate the influence of the initial laser phase on the interaction between relativistic electron and ultra-intense linear polarized laser field in a strong uniform magnetic field. It is found that the dynamic behaviour of the relativistic electron and the emission spectrum varies dramatically with different initial laser field phases. The effect of changing initial phase is contrary in the two parameter regions divided by the resonance condition. The phase dependence of the electron energy and velocity components are also studied. Some beat structure is found when the initial laser phase is zero and this structure is absent when the initial laser phase is a quarter of a period.
Influence of External Magnetic Field on Anomalous Skin Effects in Inductively Coupled Plasmas
MAO Ming, WANG You-Nian
Chin. Phys. Lett. 2004, 21 (3): 511-513 .  
Abstract   PDF(pc) (387KB) ( 320 )
Using a one-dimensional slab model, we study the influence of the external static magnetic field on the anomalous skin effects in the inductively coupled plasma. The rf electromagnetic field in the plasma is determined by solving the linearized Boltzmann equation incorporating with the Maxwell equations. The numerical results show that, due to the existence of the external magnetic field, the anomalous skin effects are greatly enhanced and the number of regions with negative absorption is decreased.

Gadolinium-Induced Multi-Effect on Properties of IR Transmitting Chalcogenide Glasses
ZHAO Dong-Hui, XIA Fang, NIE Jia-Xiang, CHEN Guo-Rong, ZHANG Xiang-Hua, MA Hong-Li, ADAM Jean-Luc
Chin. Phys. Lett. 2004, 21 (3): 514-516 .  
Abstract   PDF(pc) (443KB) ( 558 )
We introduce gadolinium in chalcogenide glasses to exert unexpectedly the multiple magical effects on both optical and thermal mechanical properties of chalcogenide glasses. Notable increases in transition temperature Tg and microhardness Hv were observed due to structural densification and microcrystallization. Calculated molar volume values, differential scanning calorimetry and x-ray diffraction measurements provide supporting evidence. Gadolinium also acts as an oxygen getter by removing or weakening oxygen-related absorption bands, which is associated with the higher negative electrode potential.

Lattice Dynamics of Potassium-Doped Single-Walled Carbon Nanotubes
XIAO Yang, YAN Xiao-Hong, CAO Jue-Xian, MAO Yu-Liang, DENG Yu-Xiang, DING Jian-Wen
Chin. Phys. Lett. 2004, 21 (3): 517-520 .  
Abstract   PDF(pc) (824KB) ( 579 )
We calculate the vibrational properties of potassium-doped single-walled carbon nanotubes within lattice dynamical theory. The results show that the frequency of high-frequency Raman mode E2g for K5C40 downshifts to 1553 cm-1, which is in agreement with the value for highly doped samples with effective composition KC8. Moreover, the specific heat curves have a turnover at 22 K, originating from the saturation of K atoms vibrational modes at low energy.
Effect of SiO2 Encapsulation on the Nitrogen Reorganization in a GaNAs/GaAs Single Quantum Well
XU Ying-Qiang, ZHANG Wei, NIU Zhi-Chuang, WU Rong-Han, WANG Qi-Ming
Chin. Phys. Lett. 2004, 21 (3): 521-523 .  
Abstract   PDF(pc) (354KB) ( 903 )
Effects of SiO2 encapsulation and rapid thermal annealing on the optical properties of a GaNAs/GaAs single quantum well (SQW) are studied by low-temperature photoluminescence (LTPL). After annealing at 800°C for 30 s, a blueshift of the LTPL peak energy for the SiO2-capped region is 25 meV and that for the bare region is 0.8 meV. The results can be attributed to the nitrogen reorganization in the GaNAs/GaAs SQW. It is also shown that the nitrogen reorganization can be obviously enhanced by the SiO2 cap-layer. A simple model is used to describe the SiO2-enhanced blueshift of the LTPL peak energy. The estimated activation energy of the N atomic reorganization for the samples annealing with and without SiO2 cap-layer are 2.9 eV and 3.1 eV, respectively.

Threshold of Non-Destructive Pulse for Pt Tip of STM on Graphite Surface
XU Chun-Kai, WEI Zheng, CHEN Xiang-Jun, XU Ke-Zun, HUANG Wen-Hao
Chin. Phys. Lett. 2004, 21 (3): 524-526 .  
Abstract   PDF(pc) (317KB) ( 600 )
The experimental relationship between width and amplitude of the non-destructive threshold pulse for Pt tip of a scanning tunnelling microscope (STM) on graphite surface have been studied strictly and systematically in a wide range of pulse width for the first time. The threshold curve of amplitude versus width indicates that the amplitude of threshold pulse will increase with the decrease of the pulse width. A more rigorous explanation is suggested to interpret the dependence of threshold pulse amplitude on width. Fitted with the experimental data, a new empirical formula is given, extrapolated from which the threshold pulse amplitude will rise to 50 V when the pulse width decreases to 10 ns.

Nitrogen Adatom Diffusion on a Ga-Rich GaN (0001) Surface
DAI Xian-Qi, WU Hua-Sheng, XIE Mao-Hai, XU Shi-Hong, TONG Shuk-Yin
Chin. Phys. Lett. 2004, 21 (3): 527-529 .  
Abstract   PDF(pc) (238KB) ( 768 )
The diffusion of N adatoms on a Ga-rich GaN(0001) surface has been studied using density-functional theory. The configuration of Ga adatoms on a Ga-rich GaN surface has been identified. The first adlayer Ga adatoms are on top of the terminating substrate Ga atoms, and the outmost adlayer Ga adatoms exist randomly at the T4 or H3 sites. A very different diffusivity of N adatoms on a Ga-rich GaN(0001) surface has been found. The excess Ga adatoms on a GaN(0001) surface reduce the diffusion barrier by 0.75 eV and influence the migration path. It seems that bilayer Ga adatoms are helpful for N atom diffusion.
Exciton Excitations in a One-Dimensional Band Insulator with Hubbard Interactions
GU Bo, LOU Ji-Zhong, QIN Shao-Jing, XIANG Tao,
Chin. Phys. Lett. 2004, 21 (3): 530-533 .  
Abstract   PDF(pc) (418KB) ( 394 )
We study the properties of exciton excitations in the Hubbard model with alternating potential and dimerized hopping terms at half-filling. With increasing Coulomb repulsion, we find that a spin triplet exciton band develops below the band gap. At certain critical interaction, the excitation gap of this exciton band vanishes and a new phase with a dimerized ground state emerges. The value of this critical Coulomb interaction is determined perturbatively.
High-Efficiency White Organic Light-Emitting Devices Based on Multiple Quantum-Well Structure
DUAN Yu, HOU Jing-Ying, WU Zhi-Jun, CHENG Gang, ZHAO Yi, LIU Shi-Yong
Chin. Phys. Lett. 2004, 21 (3): 534-536 .  
Abstract   PDF(pc) (467KB) ( 774 )
We report the white organic-light devices (WOLEDs) employing a multiple quantum-well (MQW) structure, which consist of alternate layers of 4,48-bis(2,28-diphenylvinyl)-1,18-biphenyl (DPVBi) and (DPVBi:rubrene) as the potential barrier and the potential well, respectively. The results demonstrate that the MQW structure can prominently increase the performance of WOLEDs; the double quantum well device exhibits the efficiency up to 5.4 cd/A, and yields a peak luminance of 14206 cd/m2. It is also interesting to find that the MQW structure can enhance the colour stability of WOLEDs at different voltages.

Integrability of the Inozemtsev Spin Chain with Open Boundary Conditions
XUE Wei-Xing, WANG Yu-Peng
Chin. Phys. Lett. 2004, 21 (3): 537-539 .  
Abstract   PDF(pc) (198KB) ( 828 )
A long range interacting quantum spin chain with open boundary conditions is proposed. By constructing the reflection spin-Dunkl operators, the integrability of the model is proven. The model is therefore exactly solvable via the asymptotic Bethe ansatz method and falls into the universal class of the usual Heisenberg spin chain with boundary fields.

Structural and Transport Properties for Al- and Fe-Doping La0.67Ca0.33MnO3 Perovskite Manganese
CUI Yu-Jian, JIA Guang-Qiang, HAN Yan-Bing, LI Jin-Bo, WANG Xin-Yan, GE Hong-Liang, CAO Shi-Xun, ZHANG Jin-Cang
Chin. Phys. Lett. 2004, 21 (3): 540-543 .  
Abstract   PDF(pc) (540KB) ( 517 )
The effects of Al and Fe ion doping in Mn sites was studied for the colossal La0.67Ca0.33MnO3 magnetoresistance material. It was found that when the Fe-doping amount x increases, the crystal cell structure has no obvious change, but the crystal cell volume decrease monotonically for Al-doping. Both resistances increase rapidly and the insulator-metal transition temperature moves to lower temperature and decreases linearly with Al-doping. The area for Al-doping is broader than Fe. At small amount of Al-doping, the resistance satisfy the metal transport property when T < TIM. The characteristic of the transport behaviour for Al- and Fe-doping can be explained by terminating the double exchange channel of Mn3+-O2--Mn4+.
Structural, Ferroelectric, Dielectric Properties and Leakage Characteristics of Neodymium-Doped Bi4Ti3O12 Thin Films Prepared by Metalorganic Deposition Method
LI Wei, MA Jun, SONG Chun-Hua, BAO Peng, LU Xiao-Mei, ZHU Jin-Song, WANG Ye-Ning
Chin. Phys. Lett. 2004, 21 (3): 544-547 .  
Abstract   PDF(pc) (546KB) ( 700 )
Thin films of Nd3+-substituted Bi3.15Nd0.85Ti3O12 (BNT) were fabricated on the (111 Pt/TiO2/SiO2/Si substrates by a metalorganic deposition (MOD) technique. These thin films are possessed of a single-phase bismuth-layered structure showing the preferred (001) and (117) orientation. The values of the remanent polarization Pr and coercive field Ec of the BNT thin film are 27μC/cm2 and 157 kV/cm, respectively. The results of fatigue and retention tests revealed that the BNT thin film was not fatigued up to 1.44 x 1010 switching cycles and the retained charge was unchanged after 1 x 105s. The leakage current behaviour of the BNT thin film was investigated at room temperature and their conduction mechanisms were also discussed. The I-V characteristics of the film show the ohmic behaviour for applied field lower than 40 kV/cm. Nonlinearity in the I-V behaviour was observed at an applied field above 40 kV/cm. In the high field region (E > 95 kV/cm) the sample shows Schottky emission.

Temperature-Induced Switching-Over of the Luminescence Transitions in GaInNAs/GaAs Quantum Wells
BIAN Li-Feng, JIANG De-Sheng, LIANG Xiao-Gan, LU Shu-Long
Chin. Phys. Lett. 2004, 21 (3): 548-551 .  
Abstract   PDF(pc) (468KB) ( 509 )
Photoluminescence (PL) spectra of the GaInNAs/GaAs single quantum well (SQW) with different N compositions are carefully studied in a range of temperatures and excitation power densities. The anomalous S-shape temperature dependence of the PL peak is analysed based on the competition and switching-over between the peaks related to N-induced localized states and the peak related to interband excitonic recombination. It is found that with increasing N composition, the localized energy increases and the turning point of the S-shape temperature dependence occurs at higher temperature, where the localized carriers in the band tail states obtain enough thermal activation energy to be dissociated and delocalized. The rapid thermal annealing (RTA) effectively reduces the localized energy and causes a decrease of the switching-over temperature.

Origin and Characteristics of Blue Light Emission in Solid State Cathodoluminescence of MEH-PPV
QU Chong, XU Zheng, TENG Feng, QIAN Lei, YU Wen-Ge, QUAN Shan-Yu, XU Xu-Rong,
Chin. Phys. Lett. 2004, 21 (3): 552-555 .  
Abstract   PDF(pc) (397KB) ( 421 )
Based on our previous study [Chin. Phys. Lett. 20 (2003) 1144] on the solid state cathodoluminescence from organic luminescent materials, here we study the origin and characteristics of blue light emission in solid state cathodoluminescence of Poly [(2-methoxy-5-(2'-ethyl-hexyloxy)phenylene vinyene] (MEH-PPV) and the dependence of each spectral peak on electric field strength. The results demonstrate that the blue spectral shift benefits from field ionization of excitons, and three regions of electric field are found, in which there are pure exciton emission, coexistence of exciton emission and radiative recombination, and pure radiative recombination.

Improvement of Efficiency and Brightness of Red Organic Light-Emitting Devices Using Double-Quantum-Well Configuration
MI Rui, CHENG Gang, ZHAO Yi, XIE Wen-Fa, HOU Jing-Ying, DING Tao, LIU Shi-Yong
Chin. Phys. Lett. 2004, 21 (3): 556-558 .  
Abstract   PDF(pc) (418KB) ( 573 )
We present red double-quantum-well organic light-emitting devices (DQW-OLEDs), in which N,N-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyo-4,4'-diamine (NPB) is used as potential barriers and hole transport layer, 4-(dicyanome-thylene)-2-t-butyl-6-(1,1,7,7-thtramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) doped tris (8-hydroxyquinoline) aluminium (Alq3) as potential wells and emitter, undoped Alq3 as electron transport layer, respectively. The turn-on voltage is about 4 V. The maximum brightness and electroluminescent (EL) efficiency of the DQW device can reach 5916 cd m-2 at 16 V and 2.85 cd A-1 at 7 V, respectively. In addition, the EL efficiency of the DQW device is relatively independent of the drive voltage in the range from 5 V to 16 V.

Fluorescence Spectrum Characteristics of Gold Nanorods
ZHU Jian, WANG Yong-Chang, YAN Shi-Nong
Chin. Phys. Lett. 2004, 21 (3): 559-561 .  
Abstract   PDF(pc) (452KB) ( 866 )
Aqueous solutions containing a high yield of suspended gold nanorods with mean aspect ratio 2.5 have been synthesized via an electrochemical method. The fluorescence emission peaks fixed at 370 nm and 670 nm are due to the local field enhancement via coupling to the transverse and longitudinal surface plasmon resonance. The quasi-static calculation results indicate that with the increasing aspect ratio of the nanorods, the longer wavelength emission peak decreases and red shifts, whereas the shorter wavelength emission peak blue shifts slightly.
Comparison of Secondary Ion Emissions from Carbon Nanotubes under Bombardments of MeV Si and Si2 Clusters
DING Fu-Rong, SHI Ping, HE Wei-Hong, WANG Yao, NIE Rui, SHEN Ding-Yu, MA Hong-Ji
Chin. Phys. Lett. 2004, 21 (3): 562-564 .  
Abstract   PDF(pc) (400KB) ( 457 )
The emission yields of H, H2, H3 and heavy ions from carbon nanotubes under bombardments of Si and Si2 clusters in an energy range of 0.3-3 MeV per atom are measured by using the time-of-flight technique (TOF). The emission yields of the secondary ions increase with increasing energy of Si and the electronic stopping processes play an important role. The enhanced emission yields of secondary ions induced by Si2 clusters at the low energies are clearly seen and attributed to the vicinage effect of the nuclear collision processes of cluster constituents and the secondary ion emissions are still dominated by electronic stopping processes at high energies.

Field Emission Characteristics of BN Films with Cubic-BN Phase
GU Guang-Rui, WU Bao-Jia, JIN Zhe, SUN Long, LI Jun-Jie, ZHAO Yong-Nian, WANG Bo, YAN Hui, WANG Wei-Biao
Chin. Phys. Lett. 2004, 21 (3): 565-567 .  
Abstract   PDF(pc) (332KB) ( 730 )
Boron nitride (BN) thin films with cubic boron nitride (c-BN) phase were prepared on the (100)-oriented surface of n-Si (0.008-0.02Ωm) by rf magnetron sputtering physical vapour deposition. The c-BN content is determined to be around 50% by using Fourier transform infrared spectroscopy for the BN thin films. The field emission characteristics of BN films were measured in an ultrahigh vacuum system. It is found that the field emission of the BN film with c-BN phase is evidently more excellent than that without c-BN phase. A turn-on field of 5 V/μm and a current of 460μA/cm2 were obtained for the BN film with c-BN phase. The Fowler-Nordheim plots of emission characteristics of BN films indicate a straight line, which suggests the presence of the FN tunnelling.
Theoretical Investigation of a Single Molecule Device: Geometrical Configurations and Electronic Properties
YUAN Zhe, SU Chang-Rong, ZHANG Shi-Zhong, LI Jia-Ming,
Chin. Phys. Lett. 2004, 21 (3): 568-571 .  
Abstract   PDF(pc) (412KB) ( 402 )
Using the first-principle molecular dynamics simulations, we have studied the molecular geometrical configurations as well as the corresponding electronic structures of a single molecule device assembled by the mechanically controllable break junction technique with variations of the electrode distance. There are some very interesting features varying with the electrode distance.

Wave Dispersion and Attenuation in Partially Saturated Sandstones
NIE Jian-Xin, YANG Ding-Hui, YANG Hui-Zhu
Chin. Phys. Lett. 2004, 21 (3): 572-575 .  
Abstract   PDF(pc) (424KB) ( 447 )
We investigate the wave dispersion and attenuation in partially water-saturated sandstones based on the improved Biot/squirt (BISQ) model in which the saturation is introduced. Numerical experiments indicate that the phase velocity of the fast P-wave decreases as the saturation increases in the low-frequency range (102-104 Hz), and reaches the minimum at the full-saturation state. The behaviour of the phase velocity varying with the saturation in the high-frequency range (104-106 Hz), however, is opposite to that in the low-frequency range. The peak value of P-wave attenuation increases with increasing saturation, and is the maximum at the fully saturated state. Numerical models and experiments show that the improved BISQ model is better than the traditional Gassmann-Biot model.
Ageostrophic Generalized E-P Flux in Baroclinic Atmosphere
GAO Shou-Ting, ZHANG Heng-De, LU Wei-Song
Chin. Phys. Lett. 2004, 21 (3): 576-579 .  
Abstract   PDF(pc) (386KB) ( 505 )
Aimed at limitation and deficiency of the traditional Eliassen-Palm (EP) flux associated with wave-meanflow interaction and its subsequent generalization based on the Boussinesq approximation or quasi-geostrophic approximation, we develop an ageostrophic generalized E-P flux in baroclinic stratified atmosphere. This generalized E-P flux can be conveniently used to diagnose and analyse some important phenomena related to wave-meanflow interaction of the baroclinic atmosphere with observational data, such as the upper-level jet acceleration, gravity wave breaking-up and stratospheric erupt warming.
Newtonian Forms for Dilaton Spacetimes in String Theory
YANG Rong-Jia, JING Ji-Liang
Chin. Phys. Lett. 2004, 21 (3): 580-583 .  
Abstract   PDF(pc) (212KB) ( 434 )
We show that the Newtonian forms for the motion of particles in mechanics and for light in geometrical optics can be extend to the Gibbons-Meada and the Garfinkle-Horne dilaton spacetimes in string theory. As an example, we study the bending of the light rays, the perihelion advance of a planet, and the radar echo delay in the dilaton spacetimes. The results show that the gravitational effects arising from the dilaton can be observed provided that the dilaton is large enough.
Magnetic Instability in Accretion Discs with Anomalous Viscosity
ZHOU Ai-Ping, LI Xiao-Qing
Chin. Phys. Lett. 2004, 21 (3): 584-587 .  
Abstract   PDF(pc) (419KB) ( 426 )
Using the new model of anomalous viscosity, we investigate the magnetic instability in the accretion discs and give the dispersion formula. On the basis of the dispersion relation obtained, it is numerically shown that the instability condition of the viscous accretion disc is well consistent with that of the ideal accretion disc, namely there would be magneto-rotational instability in the presence of a vertical weak magnetic field. For a given distance R from the centre of the disc, the growth rate in the anomalous case deviates from the ideal case more greatly when the vertical magnetic field is smaller. The large viscosity limits the instability. In the two cases, the distributions of growth rate with wavenumber k approach each other when the magnetic field increases. It greatly represses the effect of viscosity.
Angular Momentum in the Formation of Disc Galaxies
LUO Zhi-Jian, SHU Cheng-Gang
Chin. Phys. Lett. 2004, 21 (3): 588-591 .  
Abstract   PDF(pc) (417KB) ( 396 )
Within the current framework of disc galaxy formation, we discuss the resulted surface-density profiles according to the theoretical angular momentum distributions (AMDs) presented by Bullock et al. [Astrophys. J. 555 ,(2001) 240(B01)] for the Λ CDM cosmology in both spherical and cylindrical coordinates. It is found that the derived surface density distribution of a disc in the outer region is in general similar to an exponential disc for both the theoretical AMDs. In the central region, the results from both the theoretical AMDs are inconsistent with observations whether the disc bar-instability is taken into account or not. The cylindrical form of the theoretical AMD leads to the bar-instability more easily for a galaxy than that for spherical AMD, which could result in a more massive bulge. After comparing the model predictions with our Milky Way Galaxy, we find that the theoretical AMDs predict larger mass fractions of baryons with low angular momentum than the observed ones, which would lead to the disc sizes being smaller. Two possible processes which could solve the angular momentum problem are discussed.
An Analytical Inflation Model with Born-Infeld Type Scalar Field
HAO Jian-Gang, JIN Xing-Hua, KUANG Ji, LI Xin-Zhou
Chin. Phys. Lett. 2004, 21 (3): 592-594 .  
Abstract   PDF(pc) (187KB) ( 326 )
We propose an analytical inflation model driven by a scalar field with Born-Infeld-type Lagrangian and compute its power spectrum. The constraints on the parameters of the potential by the recent Wilkinson microwave anisotropy probe data are derived.

49 articles