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Volume 25 Issue 6
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Articles
Orbit Classification of Qutrit via the Gram Matrix
B. A. Tay, Hishamuddin Zainuddin
Chin. Phys. Lett. 2008, 25 (6): 1923-1926 .  
Abstract   PDF(pc) (231KB) ( 667 )
We classify the orbits generated by unitary transformation on the density matrices of the three-state quantum systems (qutrits) via the Gram matrix. The Gram matrix is a real symmetric matrix formed from the Hilbert--Schmidt scalar products of the vectors lying in the tangent space to the orbits. The
rank of the Gram matrix determines the dimensions of the orbits, which fall into three classes for qutrits.
A Maple Package to Compute Lie Symmetry Groups and Symmetry Reductions of (1+1)-Dimensional Nonlinear Systems
YAO Ruo-Xia, LOU Sen-Yue,
Chin. Phys. Lett. 2008, 25 (6): 1927-1930 .  
Abstract   PDF(pc) (165KB) ( 764 )
Armed with the computer algebra system Maple, using a direct algebraic substitution method, we obtain Lie point symmetries, Lie symmetry groups and the corresponding symmetry reductions of one component nonlinear integrable and nonintegrable equations only by clicking the `Enter' key. Abundant (1+1)-dimensional nonlinear mathematical physical systems are
analysed effectively by using a Maple package LieSYMGRP proposed by us.
Higher-Dimensional Integrable Systems Induced by Motions of Curves in Affine Geometries
LI Yan-Yan, QU Chang-Zheng,
Chin. Phys. Lett. 2008, 25 (6): 1931-1934 .  
Abstract   PDF(pc) (96KB) ( 653 )
We discuss the motions of curves by introducing an extra spatial variable or equivalently, moving surfaces in affine geometries. It is shown that the 2+1-dimensional breaking soliton equation and a 2+1-dimensional nonlinear evolution equation regarded as a generalization to the 1+1-dimensional KdV equation arise from such motions.
Quantum Hamilton--Jacobi Approach to Two Dimensional Singular Oscillator
Ozlem Yesiltas, Bengu Demircioglu
Chin. Phys. Lett. 2008, 25 (6): 1935-1938 .  
Abstract   PDF(pc) (116KB) ( 453 )
We obtain the solutions of two-dimensional singular oscillator which is known as the quantum Calogero--Sutherland model both in cartesian and parabolic
coordinates within the framework of quantum Hamilton Jacobi formalism. Solvability conditions and eigenfunctions are obtained by using the singularity structures of quantum momentum functions under some conditions. New potentials are generated by using the first two states of singular oscillator for parabolic coordinates.
Exact Solution of Klein--Gordon Equation by Asymptotic Iteration Method
Eser Olgar
Chin. Phys. Lett. 2008, 25 (6): 1939-1942 .  
Abstract   PDF(pc) (94KB) ( 730 )
Using the asymptotic iteration method (AIM) we obtain the spectrum of the Klein--Gordon equation for some choices of scalar and vector potentials. In particular, it is shown that the AIM exactly reproduces the spectrum of some solvable potentials.
Tractable Quantification of Entanglement for Multipartite Pure States
JIANG Nian-Quan, WANG Yu-Jian, ZHENG Yi-Zhuang, CAI Gen-Chang
Chin. Phys. Lett. 2008, 25 (6): 1943-1946 .  
Abstract   PDF(pc) (124KB) ( 482 )
We present kth-order entanglement measure and global kth-order entanglement measure for multipartite pure states, and extend Bennett's measure of partial entropy for bipartite pure states to a multipartite case. These measures are computable and can effectively classify and quantify the
entanglement of multipartite pure states.
Scheme to Implement Scheme 1→M Economical Phase-Covariant Telecloning via Cavity QED
LIU Qi, ZHANG Wen-Hai, YE Liu
Chin. Phys. Lett. 2008, 25 (6): 1947-1949 .  
Abstract   PDF(pc) (187KB) ( 564 )
We propose an experimentally feasible scheme to implement the economical 1→ M(M=2k+1) phase-covariant telecloning without ancilla based on cavity QED. The scheme requires cavity-assisted collision processes between atoms,
which cross through the off-resonant cavity field in the vacuum states. During the telecloning process, the cavity is only virtually excited and it thus greatly prolongs the efficient decoherent time. Therefore, our scheme may be realized in experiment in future.
Quantum Homodyne Detection Based on Polarization Diversity Technique
LU Yuan, ZENG Gui-Hua, YI Zhi
Chin. Phys. Lett. 2008, 25 (6): 1950-1953 .  
Abstract   PDF(pc) (102KB) ( 491 )
A polarization diversity receiver scheme is presented for improving efficiency of balance homodyne detection. The proposed scheme may mitigate polarization fluctuation between signal and local oscillator field. With simple linear optical component and electronic processing circuit, the noise caused by differential phase and polarization mode between signal and local oscillators may be significantly decreased. To track the polarization fluctuation, a novel algorithm based on polarization diversity receiver which can achieve better performance in terms of linear quantum optics principle is proposed.
Quantum Logic Network for Cloning a State Near a Given One Based on Cavity QED
ZHANG Da-Wei, SHAO Xiao-Qiang, ZHU Ai-Dong
Chin. Phys. Lett. 2008, 25 (6): 1954-1956 .  
Abstract   PDF(pc) (137KB) ( 607 )
A quantum logic network is constructed to simulate a cloning machine which copies states near a given one. Meanwhile, a scheme for implementing this cloning network based on the technique of cavity quantum electrodynamics (QED) is presented. It is easy to implement this network of cloning machine in the framework of cavity QED and feasible in the experiment.
Permutation Matrix Method for Dense Coding Using GHZ States
JIN Rui-Bo, CHEN Li-Bing, WANG Fa-Qiang, SU Zhi-Kun
Chin. Phys. Lett. 2008, 25 (6): 1957-1960 .  
Abstract   PDF(pc) (102KB) ( 461 )
We present a new method called the permutation matrix method to perform dense coding using Greenberger--Horne--Zeilinger (GHZ) states. We show that this method makes the study of dense coding systematically and regularly. It also has high potential to be realized physically.
General and Optimal Scheme for Local Conversion of Pure States
JIN Rui-Bo, CHEN Li-Bing, WANG Fa-Qiang, LU Yi-Qun
Chin. Phys. Lett. 2008, 25 (6): 1961-1963 .  
Abstract   PDF(pc) (95KB) ( 466 )
We present general and optimal schemes for local conversion of pure states, via one specific example. First, we give the general solution of the doubly stochastic matrix. Then, we find the general and optimal positive-operator-valued measure (POVM) to realize the local conversion of pure states. Lastly, the physical realization of the POVM is discussed. We show that our scheme has a more general and better effect than other schemes.
A Characteristic Non-Reflecting Boundary Treatment in Lattice Boltzmann Method
KIM Dehee, KIM Hyung Min, JHON Myung S., VINAY III Stephen J., BUCHANAN John
Chin. Phys. Lett. 2008, 25 (6): 1964-1967 .  
Abstract   PDF(pc) (250KB) ( 711 )
In lattice Boltzmann methods, disturbances develop at the initial stages of the simulation, the decay characteristics depend mainly on boundary treatment methods; open boundary conditions such as equilibrium and bounce-back schemes potentially generate uncontrollable disturbances. Excessive
disturbances originate from non-physical reflecting waves at boundaries. Characteristic boundary conditions utilizing the signs of waves at boundaries which suppress these reflecting waves, as well as their implementation in the lattice Boltzmann method, are introduced herein. The performance of our novel boundary treatment method to effectively suppress excessive disturbances is verified by three different numerical experiments.
Delocalization of Quantum Kicked Rotator with a Large Denominator
MA Tao, LI Shu-Min,
Chin. Phys. Lett. 2008, 25 (6): 1968-1971 .  
Abstract   PDF(pc) (238KB) ( 427 )
We use the iterative unitary matrix multiplication method to calculate the long-time behaviour of the resonant quantum kicked rotator with a large denominator. The delocalization time is an exponential function of the denominator. The wave function delocalizes through degenerate states. We also construct a nonresonant quantum kicked rotator with delocalization.
On the Conversion of High-Frequency Soliton Solutions to a (1+1)-Dimensional Nonlinear Partial Differential Evolution Equation
Kuetche Kamgang Victor, Bouetou Bouetou Thomas, Timoleon Crepin Kofane,
Chin. Phys. Lett. 2008, 25 (6): 1972-1975 .  
Abstract   PDF(pc) (118KB) ( 430 )
From the dynamical equation of barotropic relaxing media beneath pressure perturbations, and using the reductive perturbative analysis, we investigate the soliton structure of a (1+1)-dimensional nonlinear partial differential
evolution (NLPDE) equation ∂y (∂η+u∂y+(u2/2)∂y )u+α uy+u=0, describing high-frequency regime of perturbations. Thus, by means of Hirota's bilinearization method, three typical solutions depending strongly upon a characteristic dissipation parameter are unearthed.
Revelation of Causes of Colour Change in Beryllium-Treated Sapphires
Pichet Limsuwan, Siwaporn Meejoo, Asanee Somdee, Kheamrutai Thamaphat, Treedej Kittiauchawal, Atitaya Siripinyanond, Jurek Krzystck
Chin. Phys. Lett. 2008, 25 (6): 1976-1979 .  
Abstract   PDF(pc) (732KB) ( 810 )
Blue sapphires are treated with Be in oxidizing atmosphere to change the blue colour into yellow. Untreated and Be-treated samples are examined using laser ablation inductively coupled-plasma-mass spectrometry (LA-ICP-MS), electron spin resonance (ESR) and ultraviolet--visible (UV--vis) spectroscopy. The results show that the yellow colouration in Be-heated blue sapphires is not due to Be diffusion from the surface of sapphire. Be behaves as a sole catalyst in this process. We find that the charge transfer between the ferrous (Fe2+) and ferric (Fe3+) is the reason of the colour change. The above conclusions are confirmed by ESR measurements to determine the connections between the Fe3+ ions before and after Be-treated heat treatments.
Non-Commutative Fock--Darwin System and Magnetic Field Limits
YU Xiao-Min, LI Kang
Chin. Phys. Lett. 2008, 25 (6): 1980-1983 .  
Abstract   PDF(pc) (113KB) ( 519 )
A Fock--Darwin system in noncommutative quantum mechanics is studied. By constructing Heisenberg algebra we obtain the levels on noncommutative space and noncommutative phase space, and give the corrections to the results in usual quantum mechanics. Moreover, to search the difference among the three spaces, the degeneracy is analysed by two ways, the value
of ω/ωc and certain algebra realization (SU(2)and SU(1,1)), and some interesting properties in the magnetic field limit are exhibited, such as totally different degeneracy and magic number distribution for the given frequency or mass of a system in strong magnetic field.
Electroweak Chiral Lagrangian for Neutral Higgs Boson
WANG Shun-Zhi, WANG Qing,
Chin. Phys. Lett. 2008, 25 (6): 1984-1987 .  
Abstract   PDF(pc) (114KB) ( 442 )
A neutral Higgs boson is added into the traditional electroweak chiral Lagrangian by writing down all possible high dimension operators. The matter part of the Lagrangian is investigated in detail. We find that if Higgs field dependence of Yukawa couplings can be factorized out, there will be no flavour changing neutral couplings; neutral Higgs can induce coupling between light and heavy neutrinos.
An Approach to Extract the Spin Transfer to ∧in Polarized Proton--Proton Collision
HAN Ran, YE Hong-Xue, LIANG Yu-Tie, MAO Ya-Jun
Chin. Phys. Lett. 2008, 25 (6): 1988-1991 .  
Abstract   PDF(pc) (136KB) ( 413 )

We introduce an approach to extract the spin transfer to ∧ in polarized proton--proton collision, based on the relation between single spin asymmetry and the polarization of ∧ production. With 4×106 ∧ events simulated for a PHENIX detector system, DLL = 0.1598 \pm 0.0343$ is retrieved by the approach and it agrees very well with the input value of 0.1429. The approach is further tested and confirmed with `bunch shuffling' method for the simulated events as well as experimental events collected at PHENIX in 2003. It is concluded that one can correctly extract the spin transfer without detailed understanding of acceptance correction even if the correction is significantly large in PHENIX experiment by using the approach described here. The method can be generally used for spin transfer study.

Articles
The β Decay of 21N
LOU Jian-Ling, LI Zhi-Huan, YE Yan-Lin, JIANG Dong-Xing, HUA Hui, LI Xiang-Qing, ZHANG Shuang-Quan, ZHENG Tao, GE Yu-Chen, KONG Zan, LV Lin-Hui, LI Chen, LU Fei, FAN Feng-Ying, LI Zhong-Yu, CAO Zhong-Xin, MA Li-Ying, Faisal, XU Hu-Shan, HU Zheng-Guo, WANG Meng, LEIXiang-Guo, DUAN Li-Min, XIAO Zhi-Gang, ZHAN Wen-Long, XIAO Guo-Qing, HUANG Tian-Heng, FU Fen, ZHANG Xue-Heng, ZHENG Chuan, YU Yu-Hong, TU Xiao-Lin, ZHANG Ya-Peng, YANG Yan-Yun, ZHANG Hong-Bin, TANG Bin, TIAN Yu-Lin, OU Yang-Zhen, HUANG Mei-Rong, XU Zhi-Guo, YUE Ke, GAO Qi
Chin. Phys. Lett. 2008, 25 (6): 1992-1995 .  
Abstract   PDF(pc) (633KB) ( 460 )
The β-delayed neutron and γ energy spectra taken from the decay of neutron-rich nucleus 21N were measured by using the β-γ and β-n coincidence detection method. Thirteen new neutron groups ranging from 0.28MeV to 4.98MeV and with a total branching ratio of 88.7±4.2% were observed and
presented. One γ transition with an energy of 1222keV emitted from the excited state of 21O, and four γ transitions with energies of 1674, 2397, 2780, and 3175keV emitted from the excited states of 20O were identified in the β decay chain of 21N. The β decay half-life for 21N is determined to be 82.9±1.9ms. The uncertainty of half-life is much smaller than the previous result.
High Spin States in Odd--Odd 160Tm Nucleus
SUN Liang, LU Jing-Bin, YANG Dong, WANG Lie-Lin, YANG Sen, LIU Yun-Zuo, ZHAO Yan-Xin, ZHOU Wen-Ping, MA Ying-Jun, ZHU Li-Hua, WU Xiao-Guang, LI Guang-Sheng
Chin. Phys. Lett. 2008, 25 (6): 1996-1999 .  
Abstract   PDF(pc) (219KB) ( 490 )
High-spin states of 160Tm are studied by the 146Nd19F, 5n) reaction at a beam energy of 102MeV. The previously known π h11/2⊕υi13/2 yrast band and π h11/2⊕υh9/2 side band are confirmed. The level scheme is enriched and more low-lying levels are observed. A new side band is observed and assigned as the favoured signature partner of π d3/2⊕υi13/2. The spin of this band is assigned with the energy level systematics. It is pointed out that
the $B(M1)/B(E2)$ ratios increase rapidly at the high frequency approaching the second crossing in the π11/2υi13/2 band, which is closely related to the alignment gain of the aligned i13/2 quasineutron.
Density and Symmetric Potential Dependences of Isoscaling Behaviour in the Lattice Gas Model
SU Qian-Min, , MA Yu-Gang, TIAN Wen-Dong, FANG De-Qing, CAI Xiang-Zhou, WANG Kun
Chin. Phys. Lett. 2008, 25 (6): 2000-2003 .  
Abstract   PDF(pc) (199KB) ( 401 )
Isoscaling behaviour of the statistical emission fragments from the equilibrated sources with Z=30 and N=30, 33, 36 and 39 is investigated in the framework of the isospin-dependent lattice gas model. The dependences of isoscaling parameters α on source isospin asymmetry, temperature and
freeze-out density are studied, and the `symmetry energy' is deduced from isoscaling parameters. The results show that symmetry energy Csym is insensitive to the change of temperature but follows the power-law dependence on the freeze-out density ρ. The effect of strength of asymmetry of nucleon--nucleon interaction potential on the density dependence of the symmetry energy is discussed.
Transition Energy and Oscillator Strength of 1s22p-12nd for Fe23 ion
WANG Zhi-Wen, LI Xin-Ru, HU Mu-Hong, LIU Ying, WANG Ya-Nan
Chin. Phys. Lett. 2008, 25 (6): 2004-2007 .  
Abstract   PDF(pc) (132KB) ( 454 )
Transition energies, wavelengths and dipole oscillator strengths of 1s22p-1s2nd (3≤n≤9) for Fe23+ ion are calculated. The fine structure splittings of
1s2nd (n≤9) states for this ion are also evaluated. The higher-order relativistic contribution to the energy is estimated under a hydrogenic approximation. The quantum defect of Rydberg series 1s2nd is determined according to the quantum defect theory. The energies of any highly excited states with (n≥10) for this series can be reliably predicted using these quantum defects as input. The results in this paper excellently agree with the
experimental data available in the literature. Combining the quantum defect theory with the discrete oscillator strengths, the discrete oscillator strengths for the transitions from same given initial state 1s22p to highly excited 1s2nd states (n≥10) and the oscillator strength density corresponding to the bound--free transitions is obtained.
A Time-Dependent Approach to High-Resolution Photoabsorption Spectrum of Rydberg Atoms in Magnetic Fields
BIAN Xue-Bin, LIU Hong-Ping, SHI Ting-Yun
Chin. Phys. Lett. 2008, 25 (6): 2008-2011 .  
Abstract   PDF(pc) (140KB) ( 467 )
A robust time-dependent approach to the high-resolution photoabsorption spectrum of Rydberg atoms in magnetic fields is presented. Traditionally we have to numerically diagonalize a huge matrix to solve the eigen-problem and then to obtain the spectral information. This matrix operation requires high-speed computers with large memories. Alternatively we present a unitary but very easily parallelized time-evolution method in an inexpensive way, which is very accurate and stable even in long-time scale evolution. With this method, we perform the spectral calculation of hydrogen atom in magnetic field, which agrees well with the experimental observation. It can be extended to study the dynamics of Rydberg atoms in more complicated cases such as in combined electric and magnetic fields.
Dissociation Energies of Diatomic Molecules
FAN Qun-Chao, SUN Wei-Guo
Chin. Phys. Lett. 2008, 25 (6): 2012-2015 .  
Abstract   PDF(pc) (167KB) ( 1300 )
Molecular dissociation energies of 10 electronic states of alkali molecules of KH,7LiD, 7LiH, 6LiH, NaK, NaLi and NaRb are studied using the highest three accurate vibrational energies of each electronic state, and an improved parameter-free analytical formula which is obtained starting from the LeRoy--Bernstein vibrational energy expression near the dissociation limit. The results show that as long as the highest three vibrational energies are accurate, the current analytical formula will give accurate theoretical dissociation energies
Detheory, which are in excellent agreement with the experimental dissociation energies Deexpt.
Theoretical Investigation of Femtosecond-Resolved Photoelectron Spectrum of NaI Molecules
LIU Yu-Fang, ZHAI Hong-Sheng, GAO Ya-Li, LIU Rui-Qiong
Chin. Phys. Lett. 2008, 25 (6): 2016-2019 .  
Abstract   PDF(pc) (141KB) ( 670 )
The time-resolved photoelectron spectra (TRPES) of NaI molecules are calculated by using the time-dependent wave packet method. Two different potential energy curves (adiabatic and diabatic) are adopted in the simulation. The third peak of the photoelectron spectra presented in the adiabatic calculation is induced by the reflection of the wave packet. The oscillating of the wave packet onto the diabatic energy curve is a decreasing process. The comparison of the photoelectron spectra between the two different calculations (adiabatic and diabatic) is presented.
Observation of Nano-Dots on HOPG Surface Induced by Highly Charged Arq+ Impact
WANG Tie-Shan, YANG Xiu-Yu, B. E. O'Rourke, XU He, CHEN Liang, CHENG Rui, PENG Hai-Bo, Y. Mitsuda, Y. Yamazaki
Chin. Phys. Lett. 2008, 25 (6): 2020-2022 .  
Abstract   PDF(pc) (1635KB) ( 480 )
Highly charged ions (HCIs) have huge potential energy due to their high charge state. When a HCI reaches a solid surface, its potential energy is released immediately on the surface to cause a nano-scale defect. Thus,
HCIs are expected to be useful for solid-surface modifications on the nano-scale. We investigate the defects on a highly oriented pyrolytic graphite (HOPG) surface induced by slow highly charged Arq+ ions with impact energy of 20--2000qeV with scanning probe microscopy (SPM). In order to clarify the role of kinetic and potential energies in surface modification, the nano-defects
are characterized in lateral size and height corresponding to the kinetic energy and charge state of the HCIs. Both the potential energy and kinetic energy of the ions may influence the size of nano-defect. Since potential energy increases dramatically with increasing charge state, the potential energy effect is expected to be much larger than the kinetic energy effect in the case of extremely high charge states. This implies that pure surface
modification on the nano-scale could be carried out by slow highly charged ions. The mean size of nano-defect region could also be controlled by selecting the charge state and kinetic energy of HCI.
Electronic Stopping Power for 0.05--10MeV Protons in a Group of Organic Materials
TAN Zhen-Yu, XIA Yue-Yuan, ZHAO Ming-Wen, LIU Xiang-Dong, ZHANG Li-Ming
Chin. Phys. Lett. 2008, 25 (6): 2023-2026 .  
Abstract   PDF(pc) (123KB) ( 396 )
Electronic stopping powers for 0.05--10MeV protons in a group of organic materials are systematically calculated. The calculations are based on Ashley's
dielectric model, and an evaluation approach of optical energy loss function is incorporated into Ashley's model because no experimental optical data are available for most of the organic materials under consideration. The Barkas-effect correction and Bloch correction are included. The proton stopping powers for the considered organic materials except for mylar in the energy range from 0.05 to 10MeV are presented for the first time. The results may be useful for studies of various radiation effects in these materials and for space research.
Resonances in Electron Impact on Atomic Oxygen
WANG Yang, ZHOU Ya-Jun, JIAO Li-Guang, Kuru Ratnavelu
Chin. Phys. Lett. 2008, 25 (6): 2027-2029 .  
Abstract   PDF(pc) (162KB) ( 480 )
The momentum-space coupled-channels-optical (CCO) method is used to study the resonances in electron--oxygen collision in the energy region of 9--12eV. Present results have shown agreement with the available experimental
and theoretical results, and new positions of resonances are found by the comparison of total cross sections.
Broadening of Non-Transmission Band of Ultra-Narrow Band-Pass Filters Using Heterostructures
WANG Li, WANG Zhan-Shan, SANG Tian, WU Yong-Gang, CHEN Ling-Yan, LIU Hua-Song, JI Yi-Qin
Chin. Phys. Lett. 2008, 25 (6): 2030-2032 .  
Abstract   PDF(pc) (168KB) ( 458 )
Transmission characteristics are studied for the hybrid structures combining defect and multiple heterostructures. It is shown that the non-transmission frequency range can be substantially enlarged and the phenomenon of narrow band-pass filter can be realized by adjusting the number, position and size of the defect. The theoretical and experimental results on heterostructures containing Ta2O5/SiO2 multilayer films are presented. With
perfect non-transmission frequency range and high peak transmissivity, this structure opens a promising way to fabricate ultra-narrow band-pass filters with wide non-transmission frequency range.
Multi-Slit Diffraction of Evanescent Electromagnetic Waves
SONG Zhen-Ming, CHEN Yong-Yao, XU Bo, LI Yan-Feng, HU Ming-Lie, XING Qi-Rong, ZHANG Zhi-Gang, CHAI Lu, WANG Qing-Yue
Chin. Phys. Lett. 2008, 25 (6): 2033-2036 .  
Abstract   PDF(pc) (381KB) ( 431 )
The well-known Fraunhofer multi-slit diffraction is described as the multi-slit interference modulated by the single-slit diffraction, namely the multiplication between the single-slit diffraction factor and the multi-slit interference factor. By considering the simplified argument we show that the multi-slit diffraction of evanescent waves which are in the near-field region also has the interference and diffraction effects, and that this two-fold effect can be expressed as the convolution of the diffraction factor and the interference factor. Our conclusion could be helpful to understand the contribution of evanescent waves to the optical responses of sub-wavelength structures such as slits and grooves.
Triple Encrypted Holographic Storage and Digital Holographic System
ZHU Yi-Chao, ZHANG Jia-Sen, GONG Qi-Huang
Chin. Phys. Lett. 2008, 25 (6): 2037-2040 .  
Abstract   PDF(pc) (5981KB) ( 391 )
We propose a triple encrypted holographic memory containing a digital
holographic system. The original image is encrypted using double random
phase encryption and stored in a LiNbO3:Fe crystal with shift-multiplexing. Both the reference beams of the memory and the digital holographic system are random phase encoded. We theoretically and experimentally demonstrate the encryption and decryption of multiple images and the results show high quality and good fault tolerance. The total key length of this system is larger than 4.7×1033.
Absorption Changes Induced by Off-Resonance Driving a Degenerate Two-Level System
CAI Jin, ZHOU Hai-Tao, WANG Wen-Qi, LI Zhong-Hua, LI Tao, ZHANG Jun-Xiang
Chin. Phys. Lett. 2008, 25 (6): 2041-2044 .  
Abstract   PDF(pc) (231KB) ( 432 )
The alteration of atomic absorption via quantum coherence is observed in the degenerate two-level atomic system. It is shown that when the detuning of coupling field equals to that of probe light, i.e. two-photon resonance, the reduction of atomic absorption via electromagnetically induced transparency
occurs. However, when we tune the coupling field to two-photon off-resonance, the enhancement of absorption is obtained for the probe field. The influences of one-photon detuning and intensity of coupling field on absorption are also experimentally demonstrated.
A Single Mode Fibre Laser by Applying Self-Injection Locking with a DFB Structure
GU Chun, XU Li-Xin, MING Hai
Chin. Phys. Lett. 2008, 25 (6): 2045-2047 .  
Abstract   PDF(pc) (115KB) ( 533 )
We report a novel single-frequency fibre ring laser using self-injection locking with a distributed-feedback (DFB) fibre laser at 1550nm. The operating
wavelength is controlled by a saturable absorber and a DFB fibre laser in the ring cavity, the saturable absorber acts as a narrow band-pass filter. In the primary experiment, the laser output exceeds 100mW with the linewidth less than 2kHz. The laser is stable, and no mode-hopping is observed within eight hours. Compared with other cavity designs using spatial hole-burning, our laser shows high controllability.
An Ultra-Broadband Spatially Dispersed Regenerative Amplifier Free from Spatial Chirp
LI Chuang, LENG Yu-Xin, ZHANG Chun-Mei, LIANG Xiao-Yan, LI Ru-Xin, XUZhi-Zhan
Chin. Phys. Lett. 2008, 25 (6): 2048-2050 .  
Abstract   PDF(pc) (404KB) ( 503 )
An ultra-broadband Ti:sapphire regenerative amplifier based on spatially dispersed amplification is demonstrated experimentally. Departing from previous reports, a new design of the cavity gets the amplified pulse free from spatial chirp. Utilizing this new regenerative amplifier, chirped pulses with bandwidth (FWHM) of about 80nm are obtained, and the bandwidth is limited only by that of the incident seed pulses.
All-Optical RZ to NRZ Format Conversion Using Single SOA Assisted by Optical Band-Pass Filter
XIE Yi-Yuan, ZHANG Jian-Guo, WANG Wei-Qiang, YAN Shuang-Yi, XIE Xiao-Ping
Chin. Phys. Lett. 2008, 25 (6): 2051-2054 .  
Abstract   PDF(pc) (767KB) ( 476 )
We propose a novel all-optical format conversion from the return-to-zero (RZ) to the non-return-to-zero (NRZ) based on single semiconductor optical amplifier (SOA) and optical band-pass filter (OBF). We demonstrate the proof of the principle experiment at 10Gbps by using the test SOA and OBF converter. The format conversion can be achieved with output extinction ratio of 11.51dB. The BER is 5.5i×10-9 when the power of NRZ is -10dBm. The proposed scheme is robust and potential for applications in optical networks.
Anti-Stokes Line in an Index-Guiding Photonic Crystal Fibre with Two Zero-Dispersion Wavelengths
WANG Wei, GAO Fei, HOU Lan-Tian, ZHOU Gui-Yao,
Chin. Phys. Lett. 2008, 25 (6): 2055-2057 .  
Abstract   PDF(pc) (1141KB) ( 369 )
An index-guiding photonic crystal fibre with a small hole in the core is fabricated. The simulated results show that the first higher order mode possesses two zero-dispersion wavelengths, and the phase-matching
is possible in the anomalous dispersion regime between the two zero-dispersion wavelengths. Using 200fs Ti: sapphire laser of 820, 830 and 840nm, the anti-Stokes line around 530nm can be generated efficiently. The maximum ratio of the anti-Stokes signal energy to the pump component in the output spectrum is estimated to be 1.03 and the conversion efficiency is above 50%.
Nonlinear Optical Properties of Novel Polymeric Rare Earth Phthalocyanine Studied Using Picosecond Z-Scan Technique
ZHAO Peng, XU Song, LI Zhong-Yu, ZHANG Fu-Shi
Chin. Phys. Lett. 2008, 25 (6): 2058-2061 .  
Abstract   PDF(pc) (233KB) ( 454 )
Three novel tri-dimensional phthalocyanine polymers, with lanthanum (LaPPc), gadolinium (GdPPc) and ytterbium (YbPPc) as centric atoms, have been synthesized from a tetranuclear phthalonitrile. Third-order optical nonlinearities of these compounds in DMF solution are measured by a picosecond Z-sacn technique at 532nm. It is found that all the compounds show reverse saturation absorption and nonlinear self-focus refraction effect. The second-order molecular hyperpolarizabilities are calculated to be 1.82×10-29, 1.48×10-29 and 1.45×-29 esu for LaPPc, GdPPc and YbPPc, respectively. The differences among their nonlinear optical properties are attributed to the special tri-dimensional structure and the variation in rare earth atoms.
Experimental Investigation on Selective Excitation of Two-Pulse Coherent Anti-Stokes Raman Scattering
LI Xia, ZHANG Hui, ZHANG Xiang-Yun, ZHANG Shi-An, WANG Zu-Geng, SUN Zhen-Rong
Chin. Phys. Lett. 2008, 25 (6): 2062-2065 .  
Abstract   PDF(pc) (132KB) ( 711 )
Selective excitation of coherent anti-Stokes Raman scattering from the benzene solution is achieved by adaptive pulse shaping based on genetic algorithm, and second harmonic generation frequency-resolved optical gating (SHG-FROG) technique is adopted to characterize the original and optimal laser pulses. The mechanism for two-pulse coherent mode-selective excitation of Raman scattering is experimentally investigated by modulating the pump pulse in the frequency domain, and it is indicated that two-pulse coherent mode-selective excitation of Raman scattering mainly depends on the effective frequency components of the pump pulse related to specific vibrational mode. The experimental results suggest that two-pulse CARS has good signal-to-background ratio and high sensitivity, and it has attractive potential applications in the complicated molecular system.
Theoretical Investigation of Coherent Enhancement for Resonant Two-Photon Transitions
ZHANG Shi-An, WANG Zu-Geng, SUN Zhen-Rong
Chin. Phys. Lett. 2008, 25 (6): 2066-2069 .  
Abstract   PDF(pc) (132KB) ( 410 )
We theoretically investigate the coherent enhancement of resonant two-photon transitions (TPT) in a three-level atomic system. The TPT can be coherently enhanced by modulating spectral amplitude due to eliminating the destructive interference, though partial laser energy losses. Maximal enhancement of TPT can be achieved by modulating spectral phase due to
establishing completely constructive interference. Our research provides a theoretical basis for experimental investigation and appears to have potential application on coherent control in the complicated quantum system.
Carrier-Envelope-Phase Dependence of Emission Properties of High-Order Harmonic Generation
GE Yu-Cheng
Chin. Phys. Lett. 2008, 25 (6): 2070-2073 .  
Abstract   PDF(pc) (205KB) ( 522 )
The carrier-envelope-phase (CEP) dependence of the emission properties of high-order harmonic generation (HHG) are quantitatively investigated. Calculation shows that a two-cycle laser with CEP of 15° can produce a single energy distribution pulse peaked at 0.94 radian (rad) and spanned 1.29rad with the cutoff energy 2.9Up+Ip and a bandwidth 0.86Up (where Up is the ponderomotive potential of the laser field and Ip is the atomic ionization potential). The CEP dependence of the energy and temporal localizations of the single distribution pulse show interesting 180° periodic structures. These characteristics may be useful in optimizing attosecond x-ray sources and measurements.
Two-Dimensional Laguerre--Gaussian Asymmetric Soliton Family in Strongly Nonlocal Media
ZHONG Wei-Ping
Chin. Phys. Lett. 2008, 25 (6): 2074-2077 .  
Abstract   PDF(pc) (3383KB) ( 581 )
We demonstrate the existence of a broad class of higher-order Laguerre--Gaussian asymmetric spatial optical solitons in strongly nonlocal nonlinear media. Furthermore, we discuss specific values (q=0) of the modulation depth parameter for different rational values of the topological charge in detail. Our
results show that higher-order asymmetry spatial soliton family can exist in various forms, such as two-dimensional defect half-solitons, asymmetric single-layer and multi-layer necklace solitons.
Cooperative Quantum Cutting of Nano-Crystalline BaF2:Tb3+, Yb3+ in Oxyfluoride Glass Ceramics
CHEN Jing-Xin, YE Song, WANG Xi, QIU Jian-Rong
Chin. Phys. Lett. 2008, 25 (6): 2078-2080 .  
Abstract   PDF(pc) (581KB) ( 640 )
We report on cooperative quantum cutting in Tb3+-Yb3+ codoped glass ceramics. Precipitation of BaF2 nano-crystals is confirmed by XRD and HRTEM analysis. Near-infrared emission due to transition of Yb3+ ions under 485nm excitation indicates cooperative energy transfer from Tb3+ to Yb3+. The
quantum efficiency of this process reaches 145%. The realization of quantum cutting in glass ceramics may have promising applications in solar cells.
Influence of Gamma-Ray Irradiation on Absorption and Fluorescent Spectra of Nd:YAG and Yb:YAG Laser Crystals
SUN Dun-Lu, ZHANG Qing-Li, XIAO Jing-Zhong, LUO Jian-Qiao, JIANG Hai-He, YIN Shao-Tang
Chin. Phys. Lett. 2008, 25 (6): 2081-2084 .  
Abstract   PDF(pc) (210KB) ( 562 )
We investigate the influence of gamma-ray irradiation on the absorption and fluorescent spectra of Nd3+:Y3Al5O12 (Nd:YAG) and Yb3+:Y3Al5O12 (Yb:YAG) crystals grown by the Czochralski method. Two additional absorption (AA) bands induced by gamma-ray irradiation appear at 255nm and 340nm. The former is contributed due to Fe3+ impurity, the latter is due to Fe2+ ions and F-type colour centres. The intensity of the excitation and emission spectra as well as the fluorescent lifetime of Nd:YAG crystal decrease after the irradiation of 100Mrad gamma-ray. In contrast, the same dose irradiation does not impair the fluorescent properties of Yb:YAG crystal. These results indicate that Yb:YAG crystal possesses the advantage over Nd:YAG crystal that has better
reliability for applications in harsh radiant environment.
Significant Enhancement of Unidirectional Transmission in Asymmetrically Confined Photonic Crystal Defect Pairs
CAI Xu-Hong, LIN Xu-Sheng, LAN Sheng
Chin. Phys. Lett. 2008, 25 (6): 2085-2088 .  
Abstract   PDF(pc) (164KB) ( 489 )
By carrying out the two ideas of asymmetrical confinement and asymmetrical response into the photonic crystal (PC) structures that contain two or more nonlinear defects, we find that significantly unidirectional transmission can be
achieved while the transmission for the positive launch direction maintains at large values. Our analyses are supported by the simulation results based on the finite-difference time-domain technique.
TM-like and TE-like Modes Coupling in a Two-Dimensional Photonic Crystal Slab Composed of Truncated Cone Silicon Rods
XIONG Zhi-Gang, LI Zhi-Yuan, ZHANG Dao-Zhong
Chin. Phys. Lett. 2008, 25 (6): 2089-2092 .  
Abstract   PDF(pc) (1415KB) ( 606 )
We numerically investigate the coupling of TE-like modes and TM-like modes in a two-dimensional (2D) photonic crystal (PC) slab composed of truncated cone silicon rods. In such structures, the classification of TE-like modes and TM-like modes is generally impossible and the coupling occurs due to vertical structural asymmetries. The frequency and wavevector dependences of the mode coupling are discussed by investigating the photonic band structures, and the coupling efficiency is studied by examining the transmittance. The results show that the efficiency of mode conversion is strengthened by the vertical asymmetry and weakened by the clear small gap. These structures could be used as polarization conversion devices in integrated optics.
Optical Tamm States in Dielectric Photonic Crystal Heterostructure
GUO Ji-Yong, SUN Yong, LI Hong-Qiang, ZHANG Ye-Wen, CHEN Hong
Chin. Phys. Lett. 2008, 25 (6): 2093-2096 .  
Abstract   PDF(pc) (1305KB) ( 604 )
We investigate one-dimensional dielectric photonic crystal and optical Tamm modes formed by superposition of two band gaps and find that this kind of mode can be explained by the single negative materials tunnelling effect. A
finite-size dielectric photonic band gap can mimic one kind of effective single negative material and this property sensitively depends on the frequency location in stop-band regions and surface termination and so on. The effective impedance match and effective phase match give the precise position of the optical Tamm mode. Complete transparency via tunnelling is achieved by two opaque media and demonstrates the validity of our approach.
Approximated Vector Diffraction Theory for Readout Signal of Multi-Level Run-Length-Limited Discs
SONG Jie, XIA Si-Fei, XU Duan-Yi
Chin. Phys. Lett. 2008, 25 (6): 2097-2100 .  
Abstract   PDF(pc) (488KB) ( 408 )
Multi-level run-length-limited read-only optical storage is a kind of high density storage method. The width and height of recording marks are varied with different levels, which is the key technology for the optical storage. When
the readout signal of these discs with complex recording marks is computed by vector analysis method, it is very hard and time-consuming. Approximated vector computation combines the convenience of scalar method and precision of vector method, which is effective for multi-level run-length-limited read-only optical storage.
Fluid Sensor Based on Transmission Dip Caused by Mini Stop-Band in Photonic Crystal Slab
CAO Lei, HUANG Yi-Dong, MAO Xiao-Yu, LI Fei, ZHANG Wei, PENG Jiang-De
Chin. Phys. Lett. 2008, 25 (6): 2101-2103 .  
Abstract   PDF(pc) (581KB) ( 478 )
We propose a fluid sensor based on transmission dip caused by mini stop-band in photonic crystal slabs. Simulation results show that this novel type of sensors has large detective range (more than 1.5) and relative high sensitivity (4.3×10-5 in certain conditions). The central frequency and bandwidth of the mini stop-bands depend on the structure parameters of PC waveguides, which makes it possible to optimize the detective range and detective sensitivity.
Refraction Light Control by Constructing Output Interface Topography of Metal Waveguide Arrays
CAO Yong, WANG Pei, MIN Chang-Jun, LU Yong-Hua, YUAN Guang-Hui, MING Hai
Chin. Phys. Lett. 2008, 25 (6): 2104-2106 .  
Abstract   PDF(pc) (787KB) ( 455 )
We investigate a nanoscale metal waveguide array (MWGA) structure and demonstrate that negative refraction effect exists from the visible to infrared frequency. Our numerical analysis shows that this effect is related to output
interface of MWGAs. Refraction light would have different directions on the gradient shaped output surface as a result of phase retardation control by waveguide thickness. Finite-difference time-domain analysis shows that more sharp superdiffraction limit imaging can be obtained by constructing convex-like output interface topography.
Low-Temperature Thermal Conductance in Superlattice Nanowire with Structural Defect
WANG Xin-Jun, LIU Jing-Feng, LI Shui
Chin. Phys. Lett. 2008, 25 (6): 2107-2110 .  
Abstract   PDF(pc) (186KB) ( 372 )

Using the scattering-matrix cascading method, we investigate the effect of structural defect on the acoustic phonon transmission and thermal conductance in the superlattice nanowire at low temperatures. In the present system, the phonon transmissions exhibit quite complex oscillatory behaviour. It is found that a lateral defect in an otherwise periodic structure significantly decrease the thermal conductance and completely washes away the transmission quantization. However, the appreciable transmission quantization survives in the presence of a longitudinal defect whereas a good quantization plateau of thermal conductance emerges below the universal level in a wide temperature range with the lateral defect.

Modelling of Phase Change Heat Transfer System for Micro-channel and Chaos Simulation
LUO Xiao-Ping, CUI Z. F.
Chin. Phys. Lett. 2008, 25 (6): 2111-2114 .  
Abstract   PDF(pc) (167KB) ( 456 )
The dynamic properties for the micro-channel phase change heat transfer system are studied by theoretical method combined with experiment. Liquid--vapour interface dynamic systems are obtained by introducing disjoining pressure produced by three phase molecular interactions and Lie algebra
analysis. Experiments for 0.6mm×2mm rectangular micro-channel are carried out to obtain the pressure time serials. Power spectrum density analysis for these serials shows that the system is in chaotic state if the frequency is above 7.39Hz. The result indicates that the high heat transfer performance of the micro channel phase change system may relate to the characteristics
of chaos. The chaos attractor is drawn by the simulation of the obtained differential dynamic system under the conditions of our experiment.
Blow-up and Global Smooth Solutions for Incompressible Three-Dimensional Navier--Stokes Equations
GUO Bo-Ling, YANG Gan-Shan, PU Xue-Ke
Chin. Phys. Lett. 2008, 25 (6): 2115-2117 .  
Abstract   PDF(pc) (107KB) ( 482 )
We present some explicit self-similar blow-up solutions and some other solutions of the incompressible three-dimensional Navier--Stokes equations. These solutions indicate that in C∞ the solution of Navier--Stokes equations does not always tend to a solution of Euler equations.
An Implicit Scheme of Lattice Boltzmann Method for Sine-Gordon Equation
LAI Hui-Lin, MA Chang-Feng,
Chin. Phys. Lett. 2008, 25 (6): 2118-2120 .  
Abstract   PDF(pc) (538KB) ( 553 )
We establish an implicit scheme of lattice Boltzmann method for simulating the sine-Gordon equation, which can be transformed into the explicit one, so the computation of the scheme is simple. Moreover, the parameter θ of the
implicit scheme is independent of the relaxation time, which makes the model more flexible. The numerical results show that this method is very effective.
Onset of Unsteady Horizontal Convection in Rectangular Tank at Pr=1
SUN Liang, MA Dong-Jun, ZHANG Wei, SUN De-Jun
Chin. Phys. Lett. 2008, 25 (6): 2121-2124 .  
Abstract   PDF(pc) (388KB) ( 370 )
The horizontal convection within a rectangular tank is numerically simulated. The flow is found to be unsteady at high Rayleigh numbers. There is a Hopf bifurcation of Ra from steady solutions to periodic solutions, and the critical
Rayleigh number Rac is obtained to be Rac=5.5377×108 for the middle plume forcing at Pr=1, which is much larger than the value previously obtained. In addition, the unstable perturbations are always generated from the central jet, which implies that the onset of instability is due to velocity shear (shear instability) other than thermally dynamics (thermal instability). Finally, Paparella and Young's first hypotheses [J. Fluid Mech. 466(2002)205] about the destabilization of the flow is numerically proven, i.e. the middle plume forcing can lead to a destabilization of the flow.
Cellular Cell Bifurcation of Cylindrical Detonations
HAN Gui-Lai, JIANG Zong-Lin, WANG Chun, ZHANG Fan
Chin. Phys. Lett. 2008, 25 (6): 2125-2127 .  
Abstract   PDF(pc) (672KB) ( 600 )
Cellular cell pattern evolution of cylindrically-diverging detonations is numerically simulated successfully by solving two-dimensional Euler equations implemented with an improved two-step chemical kinetic model. From the
simulation, three cell bifurcation modes are observed during the evolution and referred to as concave front focusing, kinked and wrinkled wave front instability, and self-merging of cellular cells. Numerical research demonstrates that the wave front expansion resulted from detonation front diverging plays a major role in the cellular cell bifurcation, which can disturb the nonlinearly
self-sustained mechanism of detonations and finally lead to cell bifurcations.
Flat Solitary Waves due to a Submerged Body Moving in a Stratified Fluid
WEI Gang, SU Xiao-Bing, LU Dong-Qiang, YOU Yun-Xiang, DAI Shi-Qiang
Chin. Phys. Lett. 2008, 25 (6): 2128-2131 .  
Abstract   PDF(pc) (207KB) ( 400 )
A theoretical model for interaction of a submerged moving body with the
conjugate flow in a three-layer fluid is proposed to depict the internal
flat solitary wave, which is observed in experiments conducted by the present authors. A set of coupled nonlinear algebraic equations is derived for the interfacial displacements. The numerical results indicate that (a) the conjugate flow due to a two-dimensional body moving at the bottom possesses an apparent behaviour with two convex interfaces; (b) the solution satisfying the existence criterion is always unique near the relatively stable state of system. Theoretical analysis is qualitatively consistent with the experimental results obtained.
Phase Behaviour of Purely Repulsive Systems: Violation of Traditional van der Waals Picture
ZHOU Shi-Qi
Chin. Phys. Lett. 2008, 25 (6): 2132-2135 .  
Abstract   PDF(pc) (170KB) ( 406 )
Several purely repulsive potentials (PRP) are investigated theoretically. In contrast to the traditional van der Waals picture, it is found that normal gas--liquid transition emerges only on condition that the PRP as a function of particle separation holds a discontinuous point, or an indifferentiable point,
or is differentiable but with an additional length scale besides the hard sphere diameter.
Determination of Ionization Coefficient of Atmospheric Helium in Dielectric Barrier Discharge
LIANG Zhuo, LUO Hai-Yun, Wang Xin-Xin, LV Bo, GUAN Zhi-Cheng, WANGLi-Ming
Chin. Phys. Lett. 2008, 25 (6): 2136-2139 .  
Abstract   PDF(pc) (158KB) ( 626 )
A weakly luminous layer close to the anode is observed at time far ahead of the current pulse in dielectric barrier discharge of helium at atmospheric pressure and it is considered as the result of a very weak Townsend discharge. Based on the assumption that the space charge produced by this
Townsend discharge is too small to distort the uniform electric field in the gas gap, the electrons have more or less the same energy over the entire gap and the spatial distribution of the discharge light is proportional to the distribution of electron density. This light distribution is obtained by processing side-view photograph of discharge gap using an intensified charge coupled device camera with an exposure time of 20ns. By fitting a theoretically derived formula with the measured curve of light distribution, the Townsend electron ionization coefficient α is determined to be 31cm-1 at
E/p=3.6V・cm-1・Torr-1, which is much higher than that obtained by solving the Boltzmann equation of pure helium. It is believed that penning ionization of helium metastables with impurity of nitrogen molecules makes great contribution to the experimentally determined α value. The contribution of this
penning ionization to α is roughly estimated.
Large Relative Raman Shift for Molecules Adsorbed on Metallic Nano-particles
LI Xiao-Yun, XIA Yu-Xing, ZHAN Li, LENG Jiang-Hua
Chin. Phys. Lett. 2008, 25 (6): 2140-2143 .  
Abstract   PDF(pc) (277KB) ( 362 )
The enhancement of two order-of-magnitudes is observed in surface-enhanced Raman spectroscopy (SERS) of gases (CO, C2H2, C2H4, etc) adsorbed on nitric acid-roughened metal foil. In addition, some Raman lines of gases adsorbed on these active substrates show larger frequency shifts and linewidth broadening, compared with the Raman spectroscopy of free gases. Using the two-oscillator electromagnetic model, we explain this phenomenon. It is related to the large non-regular particles on the active substrate we prepared. It is found that the parameters of the surface-plasmon dispersion, the distance of molecules from the surface and the radius of particles play
crucial roles on the relative large Raman shifts.
Improvement of Uniformity of Inductively Coupled Plasma with a one Spiral Antenna
LI Lin-Sen, XU Xu, LIU Feng, ZHOU Qian-Hong, NIE Zong-Fu, LIANG Yi-Zi, LIANG Rong-Qing
Chin. Phys. Lett. 2008, 25 (6): 2144-2146 .  
Abstract   PDF(pc) (246KB) ( 904 )
Uniformity of inductively coupled plasma (ICP) is improved with a cone spiral antenna in our experiment. Performance of the ICP with a new type of antenna is experimentally investigated. The results indicate that the uniformity of plasma density in the radial direction is obviously improved as compared to the ICP with a planar spiral antenna. Performance of ICP is analysed with the experimental results.
Acceleration of Initially Moving Electrons by a Copropagation Intense Laser Pulse
JING Guo-Liang, YU Wei, LI Ying-Jun, SENECHA Vinod, CHEN Zhao-Yang, LEI An-Le
Chin. Phys. Lett. 2008, 25 (6): 2147-2150 .  
Abstract   PDF(pc) (142KB) ( 407 )
Acceleration of an initially moving electron by a copropagation ultra-short ultra-intense laser pulse in vacuum is studied. It is shown that when appropriate laser pulse parameters and focusing conditions are imposed, the acceleration of electron by ascending front of laser pulse can be much stronger compared to the deceleration by descending part. Consequently, the
electron can obtain significantly high net energy gain. We also report the results of the new scheme that enables a second-step acceleration of electron using laser pulses of peak intensity in the range of 1019-1020Wμm2cm2. In the first step the electron acceleration from rest is limited to energies of a few MeV, while in the second step the electron acceleration can be considerably enhanced to about 100MeV energy.
Natural Cone Formation for Fast Ignition of Laser Fusion
YANG Xiao-Qing, LEI An-Le, YU Wei, TANAKA Kazuo
Chin. Phys. Lett. 2008, 25 (6): 2151-2153 .  
Abstract   PDF(pc) (109KB) ( 407 )
We propose to utilize the leading pulse of a petawatt class laser to create a conic plasma channel in the dense plasmas. This plasma channel could serve as a natural cone to guide the main pulse to the cone tip, as behaves similarly to the physical Au cone. We estimate that the leading pulse of a petawatt
laser could create a natural cone with cone tip only about 100μm away from the edge of compressed core plasma. The natural cone formation should be compatible for a good uniform compression and efficient fast heating of the imploded fuel.
Ab Initio Study on Hypothetical Silver Nitride
DELIGOZ Engin, COLAKOGLU Kemal, CIFTCI Yasemin Oztekin
Chin. Phys. Lett. 2008, 25 (6): 2154-2157 .  
Abstract   PDF(pc) (147KB) ( 549 )

We perform the ab initio calculations based on norm-conserving pseudopotentials and density functional theory to investigate the structural, elastic, and thermodynamical properties for silver nitride (AgN) compound that is a member of the 4d transition metal group and has not been synthesized yet. The obtained results are compared with the other available theoretical
data, and the agreement is, generally, quite good. We also present the pressure-dependent behaviour of some mechanical and thermodynamical properties for the same compounds.

Hardness of Wurtzite-Structured Semiconductors
GUO Xiao-Ju, XU Bo, LIU Zhong-Yuan, YU Dong-Li, HE Ju-Long, GUO Li-Cong
Chin. Phys. Lett. 2008, 25 (6): 2158-2161 .  
Abstract   PDF(pc) (283KB) ( 680 )
Vickers hardness calculations of eleven wurtzite-structured semiconductors are performed based on the microscopic hardness model. All the parameters are obtained from first-principles calculations. There are two types of chemical bonds in wurtzite-structured crystals. The overlap populations of the two types of chemical bonds in lonsdaleite are chosen as Pc for wurtzite structure. The calculated bond ionicity values of the wurtzite-structured semiconductors are in good agreement with the ionicities from the dielectric definition. When the hardness of wurtzite-structured crystal is higher than 20GPa, our calculated Vickers hardness is within 10% accuracy. Therefore, the hardness of novel wurtzite-structured crystal could be estimated from first-principles calculations.
Modified Transition Temperature Equation for Superconductors
Aditya M. Vora
Chin. Phys. Lett. 2008, 25 (6): 2162-2164 .  
Abstract   PDF(pc) (0KB) ( 365 )
We present the replacement and modification of the Debye temperature θD by the average phonon frequency <ω> in the Rowell [Solid State Commun. 19 (1976) 1131] linear transition-temperature equation for superconducting materials. We not only improve Rowell's results but also describe the experimental results accurately and consistently for the various superconducting systems which cover the entire range of λ between 0.72 and 2.59. The proposed linear equation of the transition temperature TC is found to be better and more accurate than those of Jain and Kachhava [Can. J. Phys. 58 (1980) 1614].
Short-Time Dynamical Behaviour of Depinning Transition in the Uniformly Frustrated Two-Dimensional XY Model
NIE Qing-Miao, ZHOU Wei, LI Hai-Bin, XU Zhi-Jun, CHEN Qing-Hu
Chin. Phys. Lett. 2008, 25 (6): 2165-2168 .  
Abstract   PDF(pc) (181KB) ( 412 )
A short-time dynamic scaling approach is extended to study the depinning transition of the two-dimensional frustrated XY model driven by external currents. We investigate the scaling behaviour of depinning transition in the
XY model with three different flux densities f=1/2,1/25,1/30. The short-time scaling behaviour in the depinning transition of the two-dimensional XY model is clearly shown up. Besides the critical current, the exponent θ is obtained.
Structures and Phase Transition of GaAs under Pressure
CUI Hong-Ling, CHEN Xiang-Rong, JI Guang-Fu, WEI Dong-Qing
Chin. Phys. Lett. 2008, 25 (6): 2169-2172 .  
Abstract   PDF(pc) (163KB) ( 604 )
A first-principles plane wave method with the ultrasoft pseudopotential scheme in the frame of the density functional theory (DFT) is performed to calculate the lattice parameters a and c, the bulk modulus B0 and its pressure derivative B0' of the zinc-blende GaAs (ZB-GaAs), rocksalt GaAs (RS-GaAs),
CsCl-GaAs, NiAs-GaAs and wurtzite GaAs (WZ-GaAs). Our results are consistent with the available experimental data and other theoretical results. We also calculate the phase transition pressures among these different phases. The results are satisfactory.
Compressive Deformation Induced Nanocrystallization of a Supercooled Zr-Based Bulk Metallic Glass
GUO Xiao-Lin, SHAN De-Bin, MA Ming-Zhen, GUO Bin
Chin. Phys. Lett. 2008, 25 (6): 2173-2176 .  
Abstract   PDF(pc) (1676KB) ( 817 )
The nanocrystallization behaviour of a bulk Zr-based metallic glass subjected to compressive stress is investigated in the supercooled liquid region. Compared with annealing treatments without compressive stress, compressive deformation promotes the development of nucleation and suppresses the coarsening of nanocrystallites at high temperatures.
Structural Features of Boron-Doped Si(113) Surfaces Simulated by ab initio Calculations
LIAO Long-Zhong, LIU Zheng-Hui, ZHANG Zhao-Hui
Chin. Phys. Lett. 2008, 25 (6): 2177-2180 .  
Abstract   PDF(pc) (4728KB) ( 467 )
Based on ab initio calculations, boron-doped Si(113) surfaces have been simulated and atomic structures of the surfaces have been proposed. It has been determined that surface features of empty and filled states that are separately localized at pentamers and adatoms indicates a low surface density of B atoms, while it is attributed to heavy doping of B atoms at the
second layer that pentamers and adatoms are both present in an image of scanning tunnelling microscopy. B doping at the second layer should be balanced by adsorbed B or Si atoms beside the adatoms and inserted B interstitials below the adatoms.
Effects of Annealing on Microstructure and Optical Properties of TiO2 Sculptured Thin Films
XIAO Xiu-Di, DONG Guo-Ping, QI Hong-Ji, FAN Zheng-Xiu, HE Hong-Bo, SHAO Jian-Da
Chin. Phys. Lett. 2008, 25 (6): 2181-2184 .  
Abstract   PDF(pc) (290KB) ( 661 )
The evolution of microstructure and optical properties of TiO2 sculptured thin films under thermal annealing is reported. XRD, field emission SEM, UV-Vis-NIR spectra are employed to characterize the microstructural and optical properties. It is found that the optimum annealing temperature for linear birefringence is 500°C. The maximum of transmission difference for linear birefringence is up to 18%, which is more than twice of that in as-deposited thin films. In addition, the sample annealed at 500°C has a minimum of column angle about 12°C. The competitive process between the microstructural and optical properties is discussed in detail. Post-annealing is a useful method to improve the linear birefringence in sculptured thin films for practical applications.
Demonstration of GaN/InGaN Light Emitting Diodes on (100) β-Ga2O3 Substrates by Metalorganic Chemical Vapour Deposition
XIE Zi-Li, ZHANG Rong, XIA Chang-Tai, XIU Xiang-Qian, HAN Ping, LIU Bin, ZHAO Hong, JIANG Ruo-Lian, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2008, 25 (6): 2185-2186 .  
Abstract   PDF(pc) (290KB) ( 889 )
The growth and fabrication of GaN/InGaN multiple quantum well (MQW) light emitting diodes (LEDs) on (100) β-Ga2O3 single crystal substrates by metal-organic chemical vapour deposition (MOCVD) technique are reported. x-ray diffraction (XRD) θ-2θ scan spectroscopy is carried out on the GaN buffer layer grown on a (100) β-Ga2O3 substrate. The spectrum presents several sharp
peaks corresponding to the (100) β-Ga2O3 and (004) GaN. High-quality (0002) GaN material is obtained. The emission characteristics of the GaN/InGaN MQW LED are measurement. The first green LED on β-Ga2O3 with vertical current injection is demonstrated.
Improved Resistive Switching Characteristics of Ag-Doped ZrO2 Films Fabricated by Sol-Gel Process
SUN Bing, LIU Li-Feng, HAN De-Dong, WANG Yi, LIU Xiao-Yan, HAN Ru-Qi, KANG Jin-Feng
Chin. Phys. Lett. 2008, 25 (6): 2187-2189 .  
Abstract   PDF(pc) (404KB) ( 635 )
Ag-doped and pure ZrO2 thin films are prepared on Pt/Ti/SiO2/Si substrates by sol-gel process for resistive random access memory application. The highly reproducible resistive switching is achieved in the 10% Ag-doped ZrO2 devices. The improved resistive switching behaviour in the Ag doped ZrO2 devices could be attributed to Ag doping effect on the formation of the stable
filamentary conducting paths. In addition, dual-step reset processes corresponding to three stable resistance states are observed in the 10% Ag doped ZrO2 devices, which may be implemented for the application of multi-bit storage.
Interface Evolution of TiN/Poly Si as Gate Material on Si/HfO2 Stack
JIANG Ran, YAO Li-Ting
Chin. Phys. Lett. 2008, 25 (6): 2190-2193 .  
Abstract   PDF(pc) (197KB) ( 752 )
TiN as gate electrode in Si/HfO2/TiN/poly-Si stack is evaluated after the postmetal annealing treatments. Interface reactions are investigated using
electron-energy-loss spectroscopy and x-ray photoelectron spectroscopy. The work function of the TiN/poly-Si stack shows strong dependence on the postmetal deposition annealing conditions. The interfacial product in TiN/poly-Si interface is inferred as TiSiN, which is beneficial for the whole high-k stack since TiSiN possesses higher work function compared to TiN and poly-Si.
Spin Splitting in In0.53Ga0.47As/InP Heterostructures
SHANG Li-Yan, YU Guo-Lin, LIN Tie, ZHOU Wen-Zheng, GUO Shao-Ling, DAI Ning, CHU Jun-Hao
Chin. Phys. Lett. 2008, 25 (6): 2194-2197 .  
Abstract   PDF(pc) (153KB) ( 513 )
Spin-orbit coupling in a gate-controlled In0.53Ga0.47As/InP quantum well is
investigated in the presence of a large Zeeman effect. We develop a Fourier-transform fitting procedure to extract the zero-field spin-splitting Rashba parameter α. The bare g factor value is found to be of the order of 3 from magnetotransport measurements in tilted magnetic fields. It is found that both Zeeman splitting and Rashba splitting play important roles in determining the total spin splitting in In0.53Ga0.47As.
Spin-Polarized Transport through Parallel Double Quantum Dots Coupled to Ferromagnetic Leads
HOU Tao, WU Shao-Quan, BI Ai-Hua, YANG Fu-Bin, SUN Wei-Li
Chin. Phys. Lett. 2008, 25 (6): 2198-2201 .  
Abstract   PDF(pc) (216KB) ( 470 )
We theoretically study the spin-polarized transport phenomena of the parallel double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. The Hamiltonian is solved by means of the equation-of-motion
approach. We analyse the transmission probability of this system in both the equilibrium and nonequilibrium cases, and our results reveal that the transport properties show some noticeable characteristics depending upon both the spin-polarized strength p and the value of the magnetic flux Φ. Moreover, in the parallel configuration, the position of the Kondo peak shifts while it remains unchanged for the antiparallel configuration. These effects might have some potential applications in spintronics.
Thermoelectric Performance of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)
JIANG Feng-Xing, XU Jing-Kun, LU Bao-Yang, XIE Yu, HUANG Rong-Jin, LI Lai-Feng
Chin. Phys. Lett. 2008, 25 (6): 2202-2205 .  
Abstract   PDF(pc) (341KB) ( 1305 )
Thermoelectric (TE) performances are systematically investigated for the pellets of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with different organic additives and heating process as organic TE materials. The electrical conductivity, Seebeck coefficient and thermal conductivity versus temperature are determined, respectively. It is found that there is no distinct change for the Seebeck coefficient among each sample with the additions of dimethyl sulfoxide and ethylene glycol. The thermal conductivity measured in a wide range of temperature indicates that the PEDOT:PSS pellet have an extremely low value. The highest figure of merit (ZT= 1.75×10-3) is observed at 270K among the PEDOT:PSS pellets.
Transport Behaviour of La0.8Sr0.2AlO3 Thin Film on Oxygen Deficient SrTiO3 Substrate
QIU Jie, LU Hui-Bin, JIN Kui-Juan, LIU Guo-Zhen, YANG Guo-Zhen
Chin. Phys. Lett. 2008, 25 (6): 2206-2208 .  
Abstract   PDF(pc) (390KB) ( 363 )
La0.8Sr0.2AlO3 (LSAO) thin films are grown on SrTiO3 (STO) and MgO substrates by laser molecular beam epitaxy. The LSAO thin film on oxygen deficient STO substrate exhibits metallic behaviour over the temperature range of 80--340K. The optical transmittance spectrum indicates that the
LSAO thin films on MgO substrate are insulating at room temperature. The transport properties of LSAO thin films on STO substrates deposited in different oxygen pressure are compared. Our results indicate that oxygen vacancies in STO substrates should be mainly responsible for the transport behaviour of LSAO thin films.
Temperature-Dependent Transport Properties in Oxide p-n Junction above Room Temperature
LIU Guo-Zhen, JIN Kui-Juan, HE Meng, QIU Jie, XING Jie, LU Hui-Bin, YANGGuo-Zhen
Chin. Phys. Lett. 2008, 25 (6): 2209-2210 .  
Abstract   PDF(pc) (118KB) ( 359 )
Oxide p-n junctions of
p-SrIn0.1Ti0.9O3/n-SrNb0.01Ti0.99O3 (SITO/SNTO) are fabricated by laser molecular beam epitaxy. The current-voltage characteristics of the SITO/SNTO p-n junction are investigated mainly in the temperature range of 300--400K. The SITO/SNTO junction exhibited good rectifying behaviour over the whole
temperature range. Our results indicate a possibility of application of oxide p-n junction in higher temperatures in future electronic devices.
Single Impurity Scattering in One-Channel Spinless Luttinger Liquid
HAN Yue-Wu, XIE Hong-Yi, LIU Yu-Liang, CAI Shao-Hong, HU Lin
Chin. Phys. Lett. 2008, 25 (6): 2211-2214 .  
Abstract   PDF(pc) (116KB) ( 457 )
Using bosonization and phase shift representation, we rigorously treat backward scattering of electrons on an impurity in a one-dimensional interacting electronic system, and demonstrate that correlation exponents of the system depend on a phase shift induced by the backward scattering, and usual exponent duality of the correlation functions between ultraviolet and infrared fixed points comes from the phase shift dependence of the correlation exponents. Finally, we study the tunnelling conductance of the system at zero temperature and obtain a modified Landauer-Bütiker formula.
Superconductivity at 55K in Iron-Based F-Doped Layered Quaternary Compound Sm[O1-xFx]FeAs
REN Zhi-An, LU Wei, YANG Jie, YI Wei, SHEN Xiao-Li, LI Zheng-Cai, CHE Guang-Can, DONG Xiao-Li, SUN Li-Ling, ZHOU Fang, ZHAO Zhong-Xian
Chin. Phys. Lett. 2008, 25 (6): 2215-2216 .  
Abstract   PDF(pc) (133KB) ( 2209 )
We report the superconductivity in iron-based oxyarsenide Sm[O1-xFx]FeAs, with the onset resistivity transition temperature at 55.0K and Meissner transition at 54.6K. This compound has the same crystal structure as LaOFeAs with shrunk crystal lattices, and becomes the superconductor with the highest critical temperature among all materials besides copper oxides up to now.
Anti-Correlation between Energy-Gap and Phonon Energy for Cuprate Bi2212 Superconductor
FAN Wei
Chin. Phys. Lett. 2008, 25 (6): 2217-2220 .  
Abstract   PDF(pc) (358KB) ( 434 )
Using the electron--phonon mechanism, we explain the spatial anti-correlation between the energy-gap and the energy of phonon mode for cuprate superconductor found in tunnelling spectrum by STM measurements of Bi2212, which is the direct effect of an important relationship (or constraint) I=const, where I is superconducting parameters. By relaxing above constraint, we study the correlation of energy gap and phonon energy
when I has a distribution. We calculate a map of transition temperature in space constructing by phonon energy and the parameter of electron--phonon interaction, which is helpful for understanding of the relation.
Nodal Gap in Fe-Based Layered Superconductor LaO0.9F0.1-δFeAs Probed by Specific Heat Measurements
MU Gang, ZHU Xi-Yu, FANG Lei, SHAN Lei, REN Cong, WEN Hai-Hu
Chin. Phys. Lett. 2008, 25 (6): 2221-2224 .  
Abstract   PDF(pc) (173KB) ( 924 )
We report the specific heat measurements on the newly discovered Fe-based layered LaO0.9F 0.1-δFeAs superconductor with the onset transition temperature Tc≈28K. A nonlinear magnetic field dependence of the electronic specific heat coefficient γ(H) has been found in the low temperature limit, which is consistent with the prediction for a nodal superconductor. The maximum gap value &#8710;0≈3.4 ±0.5meV is derived by analysing γ(H) based on the d-wave model. We also detected the electronic specific heat difference between 9T and 0T in a wide temperature range, a specific heat anomaly can be clearly observed near Tc. The Debye temperature of our sample is determined to be about 315.7K. Our results suggest an unconventional mechanism for this new superconductor.
Angle Integrated Photoemission Study of SmO0.85F0.15FeAs
OU Hong-Wei, ZHAO Jia-Feng, ZHANG Yan, SHEN Da-Wei, ZHOU Bo, YANGLe-Xian, HE Cheng, CHEN Fei, XU Min, WU Tao, CHEN Xian-Hui, CHEN Yan, FENG Dong-Lai
Chin. Phys. Lett. 2008, 25 (6): 2225-2227 .  
Abstract   PDF(pc) (211KB) ( 482 )
The electronic structure of the new superconductor SmO1-xFxFeAs (x=0.15) is studied by angle-integrated photoemission spectroscopy. Our data show a sharp feature very close to the Fermi energy, and a relative flat distribution of the density of states between 0.5eV and 3eV binding energy, which agrees well with the band structure calculations considering an antiferromagnetic ground state. No noticeable gap opening is observed at 12K below the
superconducting transition temperature, indicating the existence of large ungapped regions in the Brillouin zone.
Field Dependence of π-Band Superconducting Gap in MgB2 Thin Films from Point-Contact Spectroscopy
HUANG Yan, WANG Yong-Lei, SHAN Lei, JIA Ying, YANG Huan, WEN Hai-Hu, ZHUANG Cheng-Gang, LI Qi, CUI Yi, XI Xiao-Xing,
Chin. Phys. Lett. 2008, 25 (6): 2228-2231 .  
Abstract   PDF(pc) (208KB) ( 420 )
We present the results of point-contact spectroscopy measurements on High-quality epitaxial MgB2 thin films with injected current along the c-axis. The temperature and field dependences of π-band properties with the field parallel to (H) or perpendicular to (H|| the c-axis are investigated in detail. When a magnetic field is applied, either parallel or perpendicular to the c-axis, the density of the quasiparticle state (DOS) of the π-band proliferates quickly with increasing field, while the gap amplitude of the π-band decreases slowly, which is different from the recent theoretical calculations, showing a field dependent competition between the interband scattering and the pair-breaking effects.
The Minimum Model for the Iron-Based Superconductors
LI Jian, WANG Yu-Peng
Chin. Phys. Lett. 2008, 25 (6): 2232-2234 .  
Abstract   PDF(pc) (124KB) ( 498 )
A single band t-U-J1-J2 model is proposed as the minimum model to describe the superconductivity of the newly discovered iron-based superconductors
R(O1-xFx)FeAs and RO1-xFeAs (R=La, Ce, Sm, Pr, Nd, Gd). With the mean-field approach, it is found that the pairing occurs in the d-wave channel. In the likely parameter region of the real materials, by lowering temperature, the system enters firstly the dxy superconducting phase with D4h-symmetry
and then enters the time-reversal-symmetry-broken dxy+idx2-y2 superconducting phase with C4h-symmetry.
Element Substitution Effect in Transition Metal Oxypnictide Re(O1-xFx)TAs (Re=rare earth, T=transition metal)
CHEN Gen-Fu, LI Zheng, WU Dan, DONG Jing, LI Gang, HU Wan-Zheng, ZHENGPing, LUO Jian-Lin, WANG Nan-Lin
Chin. Phys. Lett. 2008, 25 (6): 2235-2238 .  
Abstract   PDF(pc) (199KB) ( 845 )
Different element substitution effects in transition metal oxypnictide Re(O1-xFx)TAs, with Re=La, Ce, Nd, Eu, Gd, Tm, T=Fe, Ni, Ru, are studied. Similar
to the La- or Ce-based systems, we find that the pure NdOFeAs shows a strong resistivity anomaly near 145K, which is ascribed to the spin-density-wave instability. Electron doping by F increases Tc to about 50K. While in the case of Gd, Tc is reduced below 10K. The tetragonal ZrCuSiAs-type structure could not be formed for Eu or Tm substitution in our preparing process. For the Ni-based case, although both pure and F-doped LaONiAs are superconducting, no superconductivity is found when La is replaced by Ce in both the cases, instead a ferromagnetic ordering transition is likely to form at low temperature in the undoped sample. We also synthesize LaO1-xFxRuAs and CeO1-xFxRuAs compounds. The metallic behaviour is observed down to 4K.
Synthesis and Structural Study of Sr2CuO3+δ Superconductor under High Pressure
LIU Qing-Qing, WANG Fu-Ren, LI Feng-Ying, CHEN Liang-Chen, YU Ri-Cheng, JIN Chang-Qing, LI Yan-Chun, LIU Jing
Chin. Phys. Lett. 2008, 25 (6): 2239-2241 .  
Abstract   PDF(pc) (339KB) ( 599 )
A single-phase Sr2CuO3+δ superconductor is synthesized under high temperature and high pressure, in which oxygen atoms only partially occupy the apical sites next to the CuO2 planes and act as hole-dopants. The
superconducting transition temperature with Tcmax=75K is achieved in the material. Structure analysis from x-ray powder diffraction data show that this material crystallizes into a K2NiF4 structure with tetragonal unit cell of a=
3.795(3)AAand c= 12.507(1)AA. Energy-dispersive synchrotron x-ray-diffraction studies at ambient are performed on powder samples of Sr2CuO3+δ in a diamond-anvil cell at pressure up to 35GPa. Anisotropic compressibility is found. Pressure-induced isostructural phase transition might exist as revealed by the discontinuous change of crystal cell volume V with
pressure.
Novel Bilayer Structures for Short Wavelength High Density Magneto-Optical Data Storage
WANG Xian-Ying, WANG Jing, WANG Zhan-Yong, YANG Jun-He
Chin. Phys. Lett. 2008, 25 (6): 2242-2245 .  
Abstract   PDF(pc) (145KB) ( 481 )
We report a novel bi-layer thin film structure for high density magneto-optical (MO) data storage, which combines the advantages of blue wavelength and magnetically induced superresolution (MSR) recording. A double-layer system of exchange-coupled light rare-earth (LRE) element doped NdGdFeCo and traditional TbFeCo is used as the recording medium. The experimental results demonstrate that this NdGdFeCo/TbFeCo double layer has large Kerr rotation under blue wavelength. Centre aperture detection (CAD) MSR effect with temperature rising is also observed. Theoretical calculation is also carried out to verify the experimental results. These results collectively suggest that the new bilayer structure is very promising in next generation high density MO data storage.
Influence of Zn Ions Codoping on Luminescence Properties of PbWO4:RE(RE=La, Yb, Y)
XU Yan-Ling, WANG Rui, WANG Bin-Ju, LIU Wei-Hai, WANG Jia, WANG Miao, YANG Tong-Yong
Chin. Phys. Lett. 2008, 25 (6): 2246-2248 .  
Abstract   PDF(pc) (1489KB) ( 545 )
Zn and RE (RE=La, Yb, Y) ions co-doped PbWO4 (PWO) single crystal grown by the Czochralski technique are characterized by x-ray diffraction (XRD), optical
transmission spectra, and photoluminescence (PL). The doping of Zn ions shows distinct effects on the properties of PWO:RE crystals. At low concentration of Zn ions (200ppm), the luminescence intensity is quite weak for (Zn,La)-doped PWO, but is substantially strong for (Zn,Yb)-doped PWO. The blue luminescence intensity is significantly enhanced with the increasing Zn ions doping for PWO:Y. The trivalent ions codoping can increase the ratio of the blue luminescence contributing to the fast components of light yield. Yb
ions can enhance efficiency of luminescence in PWO:Yb:Zn because they may act as a luminous sensitization agent which can be involved in the efficient energy transfer and storage of the radiative process.
High-Temperature Dielectric Response and Multiscale Mechanism of SiO2/Si3N4 Nanocomposites
HOU Zhi-Ling, ZHANG Liang, YUAN Jie, SONG Wei-Li, CAO Mao-Sheng
Chin. Phys. Lett. 2008, 25 (6): 2249-2252 .  
Abstract   PDF(pc) (1489KB) ( 583 )
The high-temperature dielectric properties of SiO2/Si3N4 nanocomposites are investigated theoretically and experimentally. Its permittivities and loss tangents at the temperature ranging from room temperature to 1300°C at 9.0GHz are measured by the resonant cavity method. The SiO2/Si3N4 nanocomposites show complex dielectric behaviour at elevated temperature, and a multi-scale model is proposed to describe the dependence of the dielectric properties in the SiO2/Si3N4 on its compositional variations. Such a theory is needed so that the available property measurements could be extrapolated to other operating frequencies and temperatures.
Optimization of (002)-Oriented ZnO Film Synthesis in Sol-Gel Process and Film Photoluminescence Property
YAN Jun-Feng, ZHAO Li-Li, ZHANG Zhi-Yong
Chin. Phys. Lett. 2008, 25 (6): 2253-2256 .  
Abstract   PDF(pc) (704KB) ( 703 )
By orthogonal design theory, technological parameters of the (002)-oriented ZnO film prepared in sol-gel process are optimized. A set of technological parameters for growing highly (002)-oriented ZnO film is obtained. As a result, it is proven that the Zn2+ concentration is the most important factor to grow a highly (002)-oriented ZnO film. We take an appropriate Zn2+ concentration 0.35mol/L for the aimed film, of which photoluminescence property is better than those of the films derived from other Zn2+ concentrations precursor solution. The Zn2+ concentration either larger or smaller than 0.35mol/L leads to the (002)-oriented degree decrease of films. By employing an atom force microscope, a hexagonal atom arrangement, which indicates that the film site detected is a ZnO single crystal, is observed in the surface of the highly (002)-oriented film.
Femtosecond Optical Detection of Quasiparticle Dynamics in Single-Crystal Bi2Sr2CaCu2O8+δ
CAO Ning, WEI Yan-Feng, ZHAO Ji-Min, ZHAO Shi-Ping, YANG Qian-Sheng, ZHANG Zhi-Guo, FU Pan-Ming
Chin. Phys. Lett. 2008, 25 (6): 2257-2260 .  
Abstract   PDF(pc) (187KB) ( 655 )
Quasiparticle dynamics of an optimally doped Bi2Sr2CaCu2O8+δ single crystal is investigated by the femtosecond pump--probe technique. Temperature
dependences of amplitude of the photoinduced differential reflectivity and the relaxation time show the evidence of strong phonon bottleneck. The experimental results are analysed by the Rothwarf--Taylor model.
Red and Near-Infrared Electroluminescences from Metal-Free Phthalocyanine
FAN Zhao-Qi, CHENG Chuan-Hui, YE Kai-Qi, YU Shu-Kun, HE Wei, XIA Dao-Cheng, GUO Zhen-Qiang, SHENG Ren-Sheng, WANG Xu, DU Xi Guang, DU Guo-Tong,
Chin. Phys. Lett. 2008, 25 (6): 2261-2264 .  
Abstract   PDF(pc) (192KB) ( 662 )
Organic light emitting diodes are fabricated based on metal-free phthalocyanine (H2Pc) doped into tris-(8-hydroxyquinoline) aluminium (Alq3). The device structure is ITO/NPB (30nm)/Alq3: H2Pc(30nm)/BCP(20nm)
/Alq3(20 nm)/Al. In the light-emitting layers, H2Pc concentrations are varied from 0wt% to 100wt%. The emissions around 708nm and 800nm appear at low concentrations, while the emissions around 910nm and 930nm appear at high concentrations. The emissions around 708nm and 800nm are from H2Pc monomers. The emissions around 910nm and 930nm are from H2Pc aggregates. The dominant mechanism in the doped devices is direct charge
trapping.
Three-Step Growth Optimization of AlN Epilayers by MOCVD
PENG Ming-Zeng, GUO Li-Wei, ZHANG Jie, YU Nai-Sen, ZHU Xue-Liang, YANJian-Feng, GE Bin-Hui, JIA Hai-Qiang, CHEN Hong, ZHOU Jun-Ming
Chin. Phys. Lett. 2008, 25 (6): 2265-2268 .  
Abstract   PDF(pc) (4489KB) ( 622 )
A three-step growth process is developed for depositing high-quality aluminium-nitride (AlN) epilayers on (001) sapphire by low pressure metalorganic chemical vapour deposition (LP-MOCVD). We adopt a low temperature (LT) AlN nucleation layer (NL), and two high temperature (HT) AlN layers with different V/III ratios. Our results reveal that the optimal NL temperature is 840--880°C, and there exists a proper growth switching from low to high V/III ratio for further reducing threading dislocations (TDs). The screw-type TD density of the optimized AlN film is just 7.86×106cm-2, about
three orders lower than its edge-type one of 2×109cm-2 estimated by high-resolution x-ray diffraction (HRXRD) and cross-sectional transmission electron
microscopy (TEM).
Doped Polycrystalline 3C-SiC Films Deposited by LPCVD for Radio-Frequency MEMS Applications
ZHAO Yong-Mei, SUN Guo-Sheng, NING Jin, LIU Xing-Fang, ZHAO Wan-Shun, WANG Lei, LI Jin-Min
Chin. Phys. Lett. 2008, 25 (6): 2269-2272 .  
Abstract   PDF(pc) (4489KB) ( 626 )
Polycrystalline 3C-SiC films are deposited on SiO2 coated Si substrates by low pressure chemical vapour deposition (LPCVD) with C3H8 and SiH4 as precursors. Controlled nitrogen doping is performed by adding NH3 during SiC
growth to obtain the low resistivity 3C-SiC films. X-ray diffraction (XRD) patterns indicate that the deposited films are highly textured (111) orientation. The surface morphology and roughness are determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface features are spherulitic texture with average grain size of 100nm, and the rms roughness is 20nm (AFM 5×5μm images). Polycrystalline 3C-SiC films with highly orientational texture and good surface morphology deposited on
SiO2 coated Si substrates could be used to fabricate rf microelectromechanical systems (MEMS) devices such as SiC based filters.
Hetero-Epitaxial Diamond Single Crystal Growth on Surface of cBN Single Crystals at High Pressure and High Temperature
GAO Feng, JIA Xiao-Peng, MA Hong-An, GUO Wei, LIU Xiao-Bing
Chin. Phys. Lett. 2008, 25 (6): 2273-2276 .  
Abstract   PDF(pc) (1057KB) ( 595 )
We report a new diamond synthesis process in which cubic boron nitride single crystals are used as seeds, Fe80Ni20 alloy powder is used as catalyst/solvent and natural flake-like graphite is used as the carbon source. The samples are investigated using laser Raman spectra and x-ray diffraction (XRD). Morphology of the sample is observed by a scanning electron microscope (SEM). Based on the measurement results, we conclude that diamond single crystals have grown on the cBN crystal seeds under the conditions of high temperature 1230°C and high pressure 4.8GPa. This work provides an original method for synthesis of high quality hetero-semiconductor with cBN and diamond single crystals, and paves the way for future development.
Stress Analysis of ZnO Film with a GaN Buffer Layer on Sapphire Substrate
CUI Jun-Peng, WANG Xiao-Feng, DUAN Yao, HE Jin-Xiao, ZENG Yi-Ping,
Chin. Phys. Lett. 2008, 25 (6): 2277-2280 .  
Abstract   PDF(pc) (1154KB) ( 675 )
A 5.35-μm-thick ZnO film is grown by chemical vapour deposition technique on a sapphire (0001) substrate with a GaN buffer layer. The surface of the ZnO film is smooth and shows many hexagonal features. The full width at half
maximum of ZnO (0002) ω-rocking curve is 161 arcsec, corresponding to a high crystal quality of the ZnO film. From the result of x-ray diffraction θ-2θ scanning, the stress status in ZnO film is tensile, which is supported by Raman scattering measurement. The reason of the tensile stress in the ZnO
film is analysed in detail. The lattice mismatch and thermal mismatch are excluded and the reason is attributed to the coalescence of grains or islands during the growth of the ZnO film.
Cs+-K+ Exchange in Z-Cut KTiOPO4 Crystal Covered with Chromium Masking Layer
ZHANG Rui-Feng, LU Fei, LIAN Jie, LIU Han-Ping, LIU Xiang-Zhi, WANG Liang-Ling, WANG Ke-Ming, LU Qing-Ming
Chin. Phys. Lett. 2008, 25 (6): 2281-2284 .  
Abstract   PDF(pc) (237KB) ( 411 )
Cs+--K+ ion exchanges are performed on z-cut KTiOPO4 crystals with chromium coating covered. The temperature of ion exchange is 430°C, and the time range from 15min to 30min. The dark mode spectra of the samples are measured by the prism coupling method. The channel structures on the samples are observed by a microscope and the near field pattern of the channel waveguides are measured by the end-fire coupling method. The refractive index of the samples increases and the increments at surface are modulated due to the existence of Cr film. In the region covered by Cr film, the refractive index of the samples at the surface increases dramatically in a shallow layer. The results of energy dispersive x-ray spectra indicate that in the region covered with Cr film, Cr ions participate in the ion exchange process, and enhance the refractive index. The results may provide a possibility that achieves index enhancement and Cr doping synchronically.
Improvement of High Temperature Characteristics for SiGeC p-i-n Diodes with Carbon Incorporation
GAO Yong, LIU Jing, YANG Yuan
Chin. Phys. Lett. 2008, 25 (6): 2285-2288 .  
Abstract   PDF(pc) (167KB) ( 640 )
Temperature-dependent characteristics of SiGeC p-i-n diodes are analysed and discussed. Based on the ISE data, the temperature-dependent physical models applicable for SiGeC/Si diodes are presented. Due to the addition of carbon into the SiGe system, the thermal stability of SiGeC diodes are improved remarkably. Compared to SiGe diodes, the reverse leakage current of SiGeC diodes is decreased by 97.1% at 400K and its threshold voltage shift is reduced over 65.3% with an increasing temperature from 300K to 400K. Furthermore, the fast and soft reverse recovery characteristics are also obtained at 400K for SiGeC diodes. As a result, the most remarkable feature of SiGeC diodes is the better high-temperature characteristics and this can be applied to high temperature up to 400K.
Properties of Seamless W Sub-Micro Electrode Used for Phase Change Memory
FENG Gao-Ming, SONG Zhi-Tang, LIU Bo, FENG Song-Lin, WAN Xu-Dong
Chin. Phys. Lett. 2008, 25 (6): 2289-2291 .  
Abstract   PDF(pc) (897KB) ( 451 )
In order to improve the reliability of C-RAM devices, a seamless sub-micro W heating electrode in diameter 260nm is fabricated with standard 0.18μm CMOS processing line. Then we successfully manufacture a chalcogenide random access memory device using this seamless sub-micro W heating electrode. The results show good electrical performance, e.g. the reset current of 1.3mA and the set/reset cycle up to 109 have been achieved.
Gas Source MBE-Grown Metamorphic InGaAs Photodetectors using InAlAsBuffer and Cap Layers with Cut-off Wavelength up to 2.7
TIAN Zhao-Bing, GU Yi, WANG Kai, ZHANG Yong-Gang
Chin. Phys. Lett. 2008, 25 (6): 2292-2295 .  
Abstract   PDF(pc) (187KB) ( 448 )
We report on InP-based metamorphic InGaAs photodiodes grown by gas
source molecular beam epitaxy (MBE), in which a relatively thin compositional graded wide band-gap InxAl1-xAs buffer layer is adopted. In the photodiodes, InAlAs is also taken as cap layers, so this structure is suitable for both front and back illuminations. At room temperature the photodiodes show 50% cut-off wavelength of 2.66μm, with measured peak detectivity of 4.91×109cmHz1/2/W at 2.57μm, and the typical dark current and R0A are
7.68μA/0.94Ωcm2 and 291nA/24.29Ωcm2 at 290K and 150K respectively for the devices in diameter 300μm. Their performances are compared to the 2.5-μm cut-offphotodiodes with similar structures.
Emergence of Strange Spatial Pattern in a Spatial Epidemic Model
SUN Gui-Quan, JIN Zhen, LIU Quan-Xing, LI Li
Chin. Phys. Lett. 2008, 25 (6): 2296-2299 .  
Abstract   PDF(pc) (1485KB) ( 560 )
Pattern formation of a spatial epidemic model with nonlinear incidence rate kI2S/(1+αI2) is investigated. Our results show that strange spatial dynamics, i.e., filament-like pattern, can be obtained by both mathematical analysis and numerical simulation, which are different from the previous results in the spatial epidemic model such as stripe-like or spotted or coexistence of both pattern and so on. The obtained results well extend the finding of pattern formation in the epidemic model and may well explain the distribution of the infected of some epidemic.
Improvement of Transverse Trapping Efficiency of Optical Tweezers
MENG Bing-Huan, ZHOU Jin-Hua, ZHONG Min-Cheng, LI Yin-Mei, WU Jian-Guang, REN Hong-Liang
Chin. Phys. Lett. 2008, 25 (6): 2300-2302 .  
Abstract   PDF(pc) (117KB) ( 696 )
Transverse trapping efficiency of optical tweezers is important in many force measurement applications. For improving the transverse trapping efficiency, we propose a simple scheme in which the Gaussian beam does not fully cover the aperture of the objective. Both experiment and theoretical simulation
qualitatively demonstrate the scheme. It is expected that the results will be useful for the design of optical tweezers.
Message Spreading and Forget--Remember Mechanism on a Scale-Free Network
LI Wei, GU Jiao, CAI Xu
Chin. Phys. Lett. 2008, 25 (6): 2303-2306 .  
Abstract   PDF(pc) (513KB) ( 494 )
We study message spreading on a scale-free network, by introducing a novel forget-remember mechanism. Message, a general term which can refer to email, news, rumor or disease, etc, can be forgotten and remembered by its holder. The way the message is forgotten and remembered is governed by the forget and remember function, F and R, respectively. Both F and R are functions of history time t concerning individual's previous states, namely being active (with message) or inactive (without message). Our systematic
simulations show at the low transmission rate whether or not the spreading can be efficient is primarily determined by the corresponding parameters for F and R.
Role of Clustering Coefficient on Cooperation Dynamics in Homogeneous Networks
WU Gang, GAO Kun, YANG Han-Xin, WANG Bing-Hong
Chin. Phys. Lett. 2008, 25 (6): 2307-2310 .  
Abstract   PDF(pc) (161KB) ( 444 )
Based on previous works, we give further investigations on the Prisoners' Dilemma Game (PDG) on two different types of homogeneous networks, i.e.~the homogeneous small-world network (HSWN) and the regular ring graph. We find that the so-called resonance-like character can occur on both the networks. Different from the viewpoint in previous publications, we think the small-world effect may be unnecessary to produce this character. Therefore, over these two types of networks, we suggest a common understanding in the viewpoint of clustering coefficient. Detailed simulation results can sustain our viewpoint quite well. Furthermore, we investigate the Snowdrift Game (SG) on the same networks. The difference between the outputs of the PDG and the SG can also sustain our viewpoint.

Risk Estimate of Diseases in Scale-Free Networks
ZHANG Li-Jie, XU Xin-Jian
Chin. Phys. Lett. 2008, 25 (6): 2311-2314 .  
Abstract   PDF(pc) (144KB) ( 547 )
We investigate the effect of risk estimate on the spread of diseases by the standard susceptible--infected--susceptible (SIS) model. The perception of the
risk of being infected is explained as cutting off links among individuals, either healthy or infected. We study this simple dynamics on scale-free networks by analytical methods and computer simulations. We obtain the self-consistency form for the infection prevalence in steady states. For a given transmission rate, there exists a linear relationship between the reciprocal of the density of
infected nodes and the estimate parameter. We confirm all the results by sufficient numerical simulations.
Heterogeneity Improves Cooperation in Continuous Snowdrift Game
ZHONG Li-Xin, QIU Tian, XU Jiang-Rong
Chin. Phys. Lett. 2008, 25 (6): 2315-2318 .  
Abstract   PDF(pc) (158KB) ( 510 )
We study the networking effects on the population divergence and the increased level of cooperation in the continuous snowdrift game (CSG). In the regular world, limited interaction inhibits the occurrence of evolutionary branching. The formation of clusters defends the intermediate-investors from
intruding by high- or low-investors. In a rewired network, the collective behaviour is related to the rewiring rules. A linear relationship I=a\σa +b between the average investment and the standard deviation of the degree distribution is found.
Note on Two-Phase Phenomena in Financial Markets
JIANG Shi-Mei, CAI Shi-Min, ZHOU Tao, , ZHOU Pei-Ling
Chin. Phys. Lett. 2008, 25 (6): 2319-2322 .  
Abstract   PDF(pc) (205KB) ( 396 )
The two-phase behaviour in financial markets actually means the bifurcation phenomenon, which represents the change of the conditional probability from an unimodal to a bimodal distribution. We investigate the bifurcation phenomenon in Hang--Seng index. It is observed that the bifurcation phenomenon in financial index is not universal, but specific under certain
conditions. For Hang--Seng index and randomly generated time series, the phenomenon just emerges when the power-law exponent of absolute increment distribution is between 1 and 2 with appropriate period. Simulations on a randomly generated time series suggest the bifurcation phenomenon itself is subject to the statistics of absolute increment, thus it may not be able to reflect essential financial behaviours. However, even under the same distribution of absolute increment, the range where bifurcation phenomenon occurs is far different from real market to artificial data, which may reflect certain market information.
Annual Variation and Global Structures of The DE3 Tide
CHEN Ze-Yu, LU Da-Ren
Chin. Phys. Lett. 2008, 25 (6): 2323-2326 .  
Abstract   PDF(pc) (965KB) ( 482 )
The SABER/TIMED temperatures taken in 2002--2006 are used to delineate the tidal signals in the middle and upper atmosphere. Then the Hough mode decomposition is applied with the DE3 tide, and the overall features of the seasonal variations and the complete global structures of the tide are observed. Investigation results show that the tide is most prominent at 110km with the maximal amplitude of >9K, and exhibits significant seasonal variation with its maximum amplitude always occurring in July every year. Results from the Hough mode decomposition reveal that the tide is composed primarily of two leading propagating Hough modes, i.e., the (-3, 3) and the (-3, 4) modes, thus is equatorially trapped. Estimation of the mean amplitude of the Hough modes show that the (-3, 3) mode and (-3, 4) mode exhibit maxima at 110km and 90km, respectively. The (-3, 3) mode plays a predominant role in shaping the global latitude--height structure of the tide, e.g., the vertical scale of>50km at the equator, and the annual course. Significant influence of the (-3, 4) mode is found below 90km, where the tide exhibits anti-symmetric structure about the equator; meanwhile the tide at northern tropical latitudes exhibits smaller vertical wavelength of about 30km
A Toy Model for Magnetic Field Configurations in Black Hole Accretion Discs
GE Zhao-Jiang, WANG Ding-Xiong, LEI Wei-Hua
Chin. Phys. Lett. 2008, 25 (6): 2327-2330 .  
Abstract   PDF(pc) (615KB) ( 423 )

We discuss the feature of the magnetic field configuration arising from double counter oriented electric current-rings in the accretion disc around a Kerr black hole (BH). We discuss the relevant physical quantities corresponding to this
configuration: (1) the power and torque transferred by the large-scale magnetic field, (2) the angular momentum and energy fluxes transferred from the BH to the inner disc, (3) the radiation flux from the disc. In addition, we discuss the possibility that the closed magnetic field anchored at the disc probably evolves to the open magnetic field, which is helpful to produce the jet from the disc.

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