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Volume 31 Issue 3
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A Pseudo Arc-Length Method for Numerical Simulation of Shock Waves
WANG Xing, MA Tian-Bao, NING Jian-Guo
Chin. Phys. Lett. 2014, 31 (03): 030201 .   DOI: 10.1088/0256-307X/31/3/030201
Abstract   PDF(pc) (1106KB) ( 832 )
A pseudo arc-length method is proposed for the numerical simulation of shock wave propagations. This method passes the discontinuities and establishes adaptive moving meshes in the physical space by introducing the arc-length parameter and transforming the computational domain. Numerical experiments of the Sod problem, double Mach reflection problem and explosion problem demonstrate that this approach is more efficient than traditional numerical methods in capturing and tracking discontinuous solutions of singular or nearly singular problems.
Ground-State Properties of Superfluid Fermi Gas in Fourier-Synthesized Optical Lattices
CHEN Yan, ZHANG Ke-Zhi, WANG Xiao-Liang, CHEN Yong
Chin. Phys. Lett. 2014, 31 (03): 030301 .   DOI: 10.1088/0256-307X/31/3/030301
Abstract   PDF(pc) (758KB) ( 351 )
By employing the balance condition between the lattice potential and the interatomic interaction, we study the ground state solutions of superfluid Fermi gases in Fourier-synthesized (FS) optical lattices. The average energy of the ground state, the atoms number, and the atom density distribution of the Fermi system are analytically derived along the Bose–Einstein condensation (BEC) side to the Bardeen–Cooper–Schrieffer (BCS) side. We analyze the properties of ground state solutions at both the BEC limit and unitarity in FS optical lattices. It is found that the relative phase α between the two lattice harmonics impacts greatly on the properties of the ground state of the superfluid Fermi gas. Especially in the BCS limit, when α=π/2, the average energy presents an exponential form with the increase of the potential depth of the lattice harmonics v2. Meanwhile, there exits a minimal value. Moreover, due to the Fermi pressure, the atom density distribution at unitarity is more outstretched than that in the BEC limit. The average energy at unitarity is apparently larger than that in the BEC limit. The properties of the ground state solution exhibit very different behaviors when the system transits from the BEC side to the BCS side.
Collective Excitation and Quantum Depletion of a Bose–Einstein Condensate in a Periodic Array of Quantum Wells
XUE Rui, LI Wei-Dong, LIANG Zhao-Xin
Chin. Phys. Lett. 2014, 31 (03): 030302 .   DOI: 10.1088/0256-307X/31/3/030302
Abstract   PDF(pc) (573KB) ( 328 )
With the help of a set of exact closed-form solutions to the stationary Gross–Pitaevskii (GP) equation, we calculate the collective excitation and quantum depletion of a weakly interacting Bose gas in the presence of a periodic array of quantum wells. The excitation spectrum (Bogoliubov spectrum) is obtained from the solution of the linearized time-dependent GP equation, which develops energy bands j( p) periodic in quasi-momentum space. Moreover, we calculate the excitation strengths Zj( p) relative to the density operator and then the dynamic structure factor S( p,ω). Accordingly, the analytical expressions of quantum depletion of the system are obtained. We find that the quantum depletion is enhanced when the interatomic interactions become larger and the potential is sufficiently deep. The conditions for the possible experimental realization of our scenario are also proposed.
Charge-Related SQUID and Tunable Phase-Slip Flux Qubit
ZHAO Hu, LI Tie-Fu, LIU Jian-She, CHEN Wei
Chin. Phys. Lett. 2014, 31 (03): 030303 .   DOI: 10.1088/0256-307X/31/3/030303
Abstract   PDF(pc) (479KB) ( 250 )
A phase-slip flux qubit, exactly dual to a charge qubit, is composed of a superconducting loop interrupted by a phase-slip junction. We propose a tunable phase-slip flux qubit by replacing the phase-slip junction with a charge-related superconducting quantum interference device (SQUID) consisting of two phase-slip junctions connected in series with a superconducting island. This charge-SQUID acts as an effective phase-slip junction controlled by the applied gate voltage and can be used to tune the energy-level splitting of the qubit. In addition, we show that a large inductance inserted in the loop can reduce the inductance energy and consequently suppress the dominating flux noise of the phase-slip flux qubit. This enhanced phase-slip flux qubit is exactly dual to a transmon qubit.
Quantum Discord Behavior about Two-Qubit Heisenberg XYZ Model with Decoherence
Chin. Phys. Lett. 2014, 31 (03): 030304 .   DOI: 10.1088/0256-307X/31/3/030304
Abstract   PDF(pc) (553KB) ( 451 )
We investigate the properties of quantum discord dynamics of a two-qubit Heisenberg XYZ system which is influenced by the environmental decoherence under an external nonuniform magnetic field. It shows that the influence of the parameters on the system heavily rely on the selection of the initial states. One point shows that the environmental decoherence cannot entirely destroy the quantum correlation, and properly controlling the parameters can inhibit the decoherence. Moreover, it presents that the inhomogeneous magnetic field cannot affect the steady quantum discord (QD), while the uniform magnetic field and the anisotropy coupling constant will change the steady QD. These investigations imply that one can obtain larger steady QD values by reasonably adjusting parameters on quantum correlation in solid state systems.
Incompressible Magnetohydrodynamic Kelvin–Helmholtz Instability with Continuous Profiles
ZHAO Kai-Ge, WANG Li-Feng, YE Wen-Hua, WU Jun-Feng, LI Ying-Jun
Chin. Phys. Lett. 2014, 31 (03): 030401 .   DOI: 10.1088/0256-307X/31/3/030401
Abstract   PDF(pc) (509KB) ( 298 )
Effects of a continuous magnetic field in the direction of streaming on the incompressible Kelvin–Helmholtz instability (KHI) are investigated by solving the linear ideal magnetohydrodynamic equations. It is found that the frequency of the KHI is not influenced by the magnetic field. The magnetic field strength effect decreases the linear growth of the KHI, while the magnetic field gradient scale length effect increases its linear growth. The KHI can even be completely suppressed when the magnetic field is strong enough. The linear growth rate approaches a maximum when the magnetic field gradient scale length is large enough.
Linear and Nonlinear Anderson Localization in a Curved Potential
Claudio Conti
Chin. Phys. Lett. 2014, 31 (03): 030501 .   DOI: 10.1088/0256-307X/31/3/030501
Abstract   PDF(pc) (559KB) ( 393 )
Disorder induced localization in the presence of nonlinearity and curvature is investigated. The time-resolved three-dimensional expansion of a wave packet in a bent cigar shaped potential with a focusing Kerr-like interaction term and Gaussian disorder is numerically analyzed. A self-consistent analytical theory, in which randomness, nonlinearity and geometry are determined by a single scaling parameter, is reported, and it is shown that curvature enhances localization.
Stochastic Resonance for a SQUID with Dichotomous Resistance
LI Jing-Hui
Chin. Phys. Lett. 2014, 31 (03): 030502 .   DOI: 10.1088/0256-307X/31/3/030502
Abstract   PDF(pc) (441KB) ( 261 )
We investigate the response to the ac current for a superconducting quantum interference device (SQUID) with a dichotomous resistance. It is shown that, for some suitably selected parameters' values, stochastic resonance appears for the amplitude of the stationary average voltage of the SQUID versus the correlation time of the dichotomous noise. Our result can provide some useful insights for the investigation of the response of the SQUID (especially for the ones with the nano junctions) to the temporal-periodic signal (including the input ac current, the irradiation microwave, the detected temporal-periodic signal, and the added ac voltage).
Floquet Topological Insulator in the BHZ Model with the Polarized Optical Field
ZHU Hua-Xin, WANG Tong-Tong, GAO Jin-Song, LI Shuai, SUN Ya-Jun, LIU Gui-Lin
Chin. Phys. Lett. 2014, 31 (03): 030503 .   DOI: 10.1088/0256-307X/31/3/030503
Abstract   PDF(pc) (643KB) ( 451 )
Topological phase of newly found matter has aroused wide interests, especially related with the external periodical modulating. With the help of the Floquet theory, we investigate the possibility of externally manipulating the topological property in a HgTe/CdTe quantum well system with the polarized optical field. We give the phase diagram, showing that by modulating the parameters of the polarized optical field, especially the phase, the topological phase transition can be realized in the QW and lead to the so-called Floquet topological insulator. When the optical field is weak, the driven QSH state of QW is robust with the optical field. However, when the optical field is relatively larger, the group velocity of edge states and the gap between the bulk states exhibit certain oscillations. The implications of our results are discussed.
Coating Qualities Evaluation for Alkali-Metal Atomic Vapor Cells Based on Frustrated Total Internal Reflection
QUAN Wei, LIU Yang, CHEN Yao
Chin. Phys. Lett. 2014, 31 (03): 030701 .   DOI: 10.1088/0256-307X/31/3/030701
Abstract   PDF(pc) (477KB) ( 227 )
To realize accurate measurement of coating thickness and surface reliefs for alkali-metal vapor cells, a measurement method based on frustrated total internal reflection (FTIR) is proposed. Firstly, the phenomenon of frustrated total internal reflection and the theory of coating thickness measurement based on FTIR are introduced. Then a coating thickness measuring system based on FTIR is established and the coating thickness measuring experiment is carried out. Next, surface reliefs are obtained by analyzing distributions of the data of coating thickness. The experimental results indicate that the FTIR method can measure coating thickness exactly with an accuracy better than 2 nm, which can satisfy the evaluation of coating qualities for alkali-metal vapor cells.
Analytic Study of with the New Combined Data from Color Glass Condensate
HU Jin-Bi, SHANG Lun-Hua, SONG Xiao-Shu, CHEN Shi-Guo, ZHOU Dai-Cui, XIANG Wen-Chang
Chin. Phys. Lett. 2014, 31 (03): 032501 .   DOI: 10.1088/0256-307X/31/3/032501
Abstract   PDF(pc) (499KB) ( 285 )
We perform a global analysis of the new combined data on inclusive structure functions in electron-proton scattering at small value of Bjorken x (x≤0.01) in the framework of the color glass condensate. The new combined HERA data at small-x are studied by an analytic proton structure function. It is shown that the theoretical results of the analytic proton structure function are in agreement with the new combined experimental data. The longitudinal proton structure function is investigated with the analytic expression. It is demonstrated that our approach shows a very good description of the longitudinal structure function experimental data, which is evidence showing the saturation effect is a domination mechanism during the rapidity evolution of the gluon density at high energy.
Study of Thick Gaseous Electron Multipliers Gain Stability and Some Influencing Factors
ZHOU Xiao-Kang, LIU Qian, CHEN Shi, HUANG Wen-Qian, WANG Bin-Long, ZHANG Yong-Dong, GE Dong-Sheng, LIU Hong-Bang, ZHENG Yang-Heng, XIE Yi-Gang, DONG Yang, ZHANG Qiang, CHANG Jie, WANG Jing, LI Min, ZHOU Yan
Chin. Phys. Lett. 2014, 31 (03): 032901 .   DOI: 10.1088/0256-307X/31/3/032901
Abstract   PDF(pc) (609KB) ( 313 )
The working stability of thinner-thick gaseous electron multipliers (THGEMs), which have been developed by the University of the Chinese Academy of Sciences and the Second Academy of China's Aerospace Science and Industry Corporation, is studied with an 8 keV x-ray on a Cu target. Gains of about 103–104 are achieved with a single board in Ar:iC4H10 (97:3). Environmental factors, such as pressure, temperature and humidity are considered. The thinner-THGEMs are shown to perform stably over two months of studies.
Electron Impact Excitation of Xenon from the Ground State and the Metastable State to the 5p57p Levels
CHEN Zhan-Bin, DONG Chen-Zhong, XIE Lu-You, JIANG Jun
Chin. Phys. Lett. 2014, 31 (03): 033401 .   DOI: 10.1088/0256-307X/31/3/033401
Abstract   PDF(pc) (734KB) ( 297 )
Electron impact excitation cross sections from the ground state and the lowest metastable state 5p56s J=2 to the excited states of the 5p57p configuration of xenon are calculated systematically using the fully relativistic distorted wave method. Special attention is paid to the configuration interaction effects in the wave-function expansion of target states. The results are in good agreement with the recent experimental data by Jung et al. [Phys. Rev. A 80 (2009) 062708] over the measured energy range. These accurate theoretical results can be used in the modeling and diagnosis of plasmas containing xenon.
Inclusion of Finite Permeability on Design and Optimization of an Electromagnetic Undulator
Vijay Huse, Geetanjali Sharma, Swati Mishra, G. Mishra
Chin. Phys. Lett. 2014, 31 (03): 034101 .   DOI: 10.1088/0256-307X/31/3/034101
Abstract   PDF(pc) (487KB) ( 298 )
We derive an alternate analytical expression for the optimum dimensions of an electromagnetic undulator with a finite permeability lamination core. The analytical expressions are compared with earlier results under an infinite permeability approximation of the lamination core of the electromagnetic undulator design.
High Refractive Index without Absorption in a Ladder-Type System
ZENG Zhi-Qiang, HOU Bang-Pin, LIU Fu-Ti, SHAO Ju-Xiang
Chin. Phys. Lett. 2014, 31 (03): 034201 .   DOI: 10.1088/0256-307X/31/3/034201
Abstract   PDF(pc) (488KB) ( 222 )
A three-level ladder-type system with vacuum-induced coherence and incoherent pumping is studied to obtain a high refractive index without absorption. It is shown that the enhancement of the refractive index without absorption can be accomplished by choosing the proper values of the incoherent pumping, the angle between the two dipole moments, the probe detuning and the relative phase of the two coherent fields.
Analysis and Simulation of Quantum Radar Cross Section
LIU Kang, XIAO Huai-Tie, FAN Hong-Qi
Chin. Phys. Lett. 2014, 31 (03): 034202 .   DOI: 10.1088/0256-307X/31/3/034202
Abstract   PDF(pc) (675KB) ( 1219 )
We derive a modified analytical expression of a quantum radar cross section (QRCS). Subsequently, we present a comparison between the QRCS and a classical radar cross section (RCS) and analyze the factors that can affect the intensity of the peak and side lobes. Simulation results on a flat rectangular plate demonstrate that QRCS has a similar structure to that of RCS. The analysis of side-lobe structure can benefit the design of quantum stealth platforms as well as the research on quantum radars.
Analysis and Measurement of the Displacement Sensor Based on an Up-tapered Mach–Zehnder Interferometer
WEN Xiao-Dong, NING Ti-Gang, YOU Hai-Dong, KANG Ze-Xin, LI Jing, LI Chao, FENG Ting, YU Shao-Wei, JIAN Wei
Chin. Phys. Lett. 2014, 31 (03): 034203 .   DOI: 10.1088/0256-307X/31/3/034203
Abstract   PDF(pc) (705KB) ( 326 )
A displacement sensor based on an up-tapered Mach–Zehnder interferometer (MZI) is proposed and demonstrated experimentally. For this purpose, a fiber MZI is fabricated by using a commercial fusion splicer. Then the transmission spectra of the sensors with different middle fiber lengths are measured by bending the MZIs with different movements of the moving stage. The maximum sensitivity of 2.457 nm/mm is achieved while the shifting of the moving stage changes from 3 mm to 3.5 mm. Note that this kind of up-taper configuration is strong in strength, easy to fabricate and low in cost.
Passively Q-Switched EDFL Using a Multi-Walled Carbon Nanotube Polymer Composite Based on a Saturable Absorber
F. Ahmad, H. Haris, R. M. Nor, N. R. Zulkepely, H. Ahmad, S. W. Harun
Chin. Phys. Lett. 2014, 31 (03): 034204 .   DOI: 10.1088/0256-307X/31/3/034204
Abstract   PDF(pc) (436KB) ( 531 )
A stable passive Q-switched erbium-doped fiber laser (EDFL) operating at 1563.5 nm is demonstrated by using a multi-walled carbon nanotube (MWCNT) polymer composite film based saturable absorber for the first time. The composite is prepared by mixing the MWCNTs homogeneous solution into a dilute PEO polymer solution before it is left to dry at room temperature to produce thin film. Then the film is sandwiched between two FC/PC fiber connectors and is integrated into the laser cavity for Q-switching pulse generation. The EDFL generates a stable pulse train with repetition rates ranging from 4.5 kHz to 20.0 kHz by varying the 1480 nm pump power from 35 mW to 53 mW. At the 53 mW pump power, the pulse width and pulse energy are 8.8 μs and 15.3 nJ, respectively.
Experimental Generation of Narrow-Band Paired Photons: from Damped Rabi Oscillation to Group Delay
LIAO Kai-Yu, YAN Hui, HE Jun-Yu, HUANG Wei, ZHANG Zhi-Ming, ZHU Shi-Liang
Chin. Phys. Lett. 2014, 31 (03): 034205 .   DOI: 10.1088/0256-307X/31/3/034205
Abstract   PDF(pc) (747KB) ( 328 )
We report the experimental generation of narrow-band paired photons through electromagnetically induced transparency and spontaneous four-wave mixing in a two-dimensional magneto-optical trap (2D MOT). By controlling the optical depth of the 2D MOT from 0 to 40, the temporal length of the generated narrow-band paired photons can be varied from 50 to 900 ns. The 'transition' between damped Rabi oscillation and group delay is observed undisputedly. In the damped Rabi oscillation regime, a violation factor of the Cauchy–Schwartz inequality as large as 6642 is observed. In the group delay regime, sub-MHz linewidth (~0.65 MHz) paired photons are obtained with a generation rate of about 0.8×105 s?1.
Effect of Spontaneously Generated Coherence and Detuning on 2D Atom Localization in Two Orthogonal Standing-Wave Fields
ZHAO Shun-Cai, WU Qi-Xuan, GONG Ai-Ling
Chin. Phys. Lett. 2014, 31 (03): 034206 .   DOI: 10.1088/0256-307X/31/3/034206
Abstract   PDF(pc) (1371KB) ( 238 )
Two-dimensional (2D) atom localization via the spontaneously generated coherence (SGC) and detunings associated with the probe and standing-wave driving fields in a three-level V-type atomic system are investigated. In the gain process, two equal and tunable peak maxima of position distribution in the – plane via the detunings are observed. However, one decreasing and the other increasing peak maxima in the absorption process via the SGC are achieved in the quadrants I and III of the xy plane. A better resolution and more novelty for the 2D atom localization in our scheme are obtained.
Evaluation of Slow Light Periodic Signals Considering the Distortion in EDF
WANG Fu, WU Chong-Qing, WANG Zhi, LIU Guo-Dong, LIU Lan-Lan, SUN Zhen-Chao
Chin. Phys. Lett. 2014, 31 (03): 034207 .   DOI: 10.1088/0256-307X/31/3/034207
Abstract   PDF(pc) (658KB) ( 225 )
Based on the fundamental harmonic phase delay, a new definition of fundamental harmonic fractional delay (FHFD) is proposed to evaluate slow light with the consideration of signal distortion, to eliminate the dependence on the choice of the reference point. By solving the rate equation of erbium-doped fiber (EDF), it is shown that the slow light always accompanies the signal distortion when the periodic signal propagates in EDF, and FHFD depends on the signal distortion, as well as the average input power, the modulation depth and the length of EDF. The results of simulations and experiments indicate that the definition of FHFD is reasonable and effective to evaluate the slow light of periodic signals.
Scattering of S0 Lamb Mode from a Blind Hole in a Plate Using Mindlin/Mindlin Plate Theory
ZHANG Hai-Yan, YAO Jie-Cong, MA Shi-Wei
Chin. Phys. Lett. 2014, 31 (03): 034301 .   DOI: 10.1088/0256-307X/31/3/034301
Abstract   PDF(pc) (670KB) ( 384 )
An analytical model of Lamb wave scattering from a circular blind hole in isotropic plates is presented using the Mindlin plate theory for describing in-plane and flexural wave modes simultaneously. The model makes use of the wave function expansion technique and the boundary conditions at the hole edge to evaluate the scattered far fields of three fundamental guided wave modes. Comparisons are made to existing approximate models using Poisson/Kirchhoff theory and Poisson/Mindlin theory and a 3D model using the exact 3D equations. The results reveal that the present model is more consistent with the exact 3D model at higher frequencies than existing approximate models.
Real-Time Monitoring and Quantitative Evaluation of Cavitation Bubbles Induced by High Intensity Focused Ultrasound Using B-Mode Imaging
YU Jie, CHEN Chu-Yi, CHEN Gong, GUO Xia-Sheng, MA Yong, TU Juan, ZHANG Dong
Chin. Phys. Lett. 2014, 31 (03): 034302 .   DOI: 10.1088/0256-307X/31/3/034302
Abstract   PDF(pc) (1805KB) ( 1107 )
A software-based method is proposed to eliminate the flooding interference strips in B-mode images, and to evaluate the cavitation bubbles generated during high intensity focused ultrasound (HIFU) exposures. In vitro tissue phantoms are exposed to 1.12 MHz HIFU pulses with a fixed 100 Hz pulse repetition frequency. HIFU-induced cavitation bubbles are detected as hyperechoic regions in B-mode images. The temporal evolution of cavitation bubbles, generated by HIFU pulses with varying driving amplitude and pulse length, is analyzed by measuring the time-varying area of the hyperechoic region. The results show that: first, it is feasible to monitor HIFU-induced cavitation bubble activity in real-time using B-mode imaging; second, more cavitation bubbles can be generated with higher acoustic energy delivered; third, the hyperechoic region is observed to shrink gradually after ceasing the HIFU pulses, which indicates the dissolution of cavitation bubbles. This work will be helpful for developing an effective tool to realize real-time monitoring and quantitative evaluation of HIFU-induced cavitation bubble activity using a current commercialized B-mode machine.
Transient Appearance of Double Spontaneous-Snakes in EAST H Mode Plasma
XU Li-Qing, HU Li-Qun, ZHANG Zi-Jun
Chin. Phys. Lett. 2014, 31 (03): 035201 .   DOI: 10.1088/0256-307X/31/3/035201
Abstract   PDF(pc) (668KB) ( 220 )
Transient lasting of double spontaneous snakes is observed in energy confinement improved plasma on the EAST tokamak. The destabilization of snakes with superb particle confinement can lower plasma energy confinement and slow plasma toroidal rotation. The non-monotonic q profile with double q=1 surface, slightly above unity in central, is constructed. The prevailing harmonic modes are susceptible to the nearly zero magnetic shear. Finally, the role of anomalous particle transport and the formation of off-axis peaking electron profile on the excitation of double snakes are discussed.
Transport Coefficients of High Temperature SF6 in Local Thermodynamic Equilibrium Using a Phenomenological Approach
WANG Wei-Zong, RONG Ming-Zhe, YANG Fei, WU Yi
Chin. Phys. Lett. 2014, 31 (03): 035202 .   DOI: 10.1088/0256-307X/31/3/035202
Abstract   PDF(pc) (588KB) ( 352 )
The transport coefficients of high temperature sulfur hexafluoride (SF6) plasmas in local thermodynamic equilibrium are calculated using collision integrals derived in a phenomenological approach which could be a valuable tool in the calculation of complete data sets for complex mixtures, including interactions hardly handled in the accurate multipotential methods. A systematic comparison with transport coefficients obtained using an old data set and experimental test is performed to check the reliability of the proposed approach in evaluating transport cross sections.
Numerical Simulation on the Production Mechanism of Surface-Wave Plasmas Sustained along a Metal Rod
ZHU Long-Ji, CHEN Zhao-Quan, YIN Zhi-Xiang, WANG Guo-Dong, XIA Guang-Qing, HU Ye-Lin, ZHENG Xiao-Liang, ZHOU Meng-Ran, CHEN Ming, LIU Ming-Hai
Chin. Phys. Lett. 2014, 31 (03): 035203 .   DOI: 10.1088/0256-307X/31/3/035203
Abstract   PDF(pc) (862KB) ( 262 )
For interpreting the production mechanism of surface-wave plasmas sustained along a metal rod, electromagnetic simulation on the electromagnetic field distributions and particle-in-cell/Monte Carlo collision (PIC/MCC) simulation of the ionization process are present. The results show that the enhanced electric field of surface plasmon polaritons (SPPs) can be excited in the ion sheath layer between the negative-voltage metal rod and the surface-wave plasmas, which is responsible for maintaining the plasma discharge. Moreover, the spatio-temporal evolutions of plasma density and electric fields are simulated by the PIC/MCC model. It is further suggested that the expanded ion sheath layer can extend the length of plasma domain by increasing the plasma absorbed energy from SPPs.
Spatially Resolved N2(A3Σ+u, ν=0) Decay Studies in the Pulsed Direct-Current Nitrogen Discharge using the Laser-Induced-Fluorescence Technique
FENG Chun-Lei, YANG Hong-Liang, GAO Liang, DING Hong-bin
Chin. Phys. Lett. 2014, 31 (03): 035204 .   DOI: 10.1088/0256-307X/31/3/035204
Abstract   PDF(pc) (817KB) ( 214 )
We focus on the investigation of the spatial distribution and temporal evolution of N2(A3Σ+u, ν=0) in a very early afterglow of a pulsed dc nitrogen discharge. The results indicate that a fast quenching process of N2(A3Σ+u, ν=0) exists in the very early afterglow. We study the dependence of this fast quenching process on the discharge pressure 20–40 torr. It seems that this fast quenching behavior of N2(A3Σ+u, ν=0) found in our experiment can be ascribed to the combined action of pooling reaction and collisions with N atoms through N2(A3Σ+u)+N2(A3Σ+u)→ N2?+N2(N2?=N2(B3Πg, C3Πu, C'3Πu, C"5Πu)) and N2(A3Σ+u)+N(4S)→N(2P)+N2, respectively. Meanwhile, the decay studies of N2(A3Σ+u, ν=0) near the anode and cathode infer that the production of N(4S) atoms does not distribute uniformly along the axis of the discharge gap at relatively low pressure, and this effect becomes gradually inconspicuous with the increasing discharge pressure.
Helium-Implantation-Induced Damage in NHS Steel Investigated by Slow-Positron Annihilation Spectroscopy
LI Yuan-Fei, SHEN Tie-Long, GAO Xing, GAO Ning, YAO Cun-Feng, SUN Jian-Rong, WEI Kong-Fang, LI Bing-Sheng, ZHANG Peng, CAO Xing-Zhong, ZHU Ya-Bin, PANG Li-Long, CUI Ming-Huan, CHANG Hai-Long, WANG Ji, ZHU Hui-Ping, WANG Dong, SONG Peng, SHENG Yan-Bin, ZHANG Hong-Peng, HU Bi-Tao, WANG Zhi-Guang
Chin. Phys. Lett. 2014, 31 (03): 036101 .   DOI: 10.1088/0256-307X/31/3/036101
Abstract   PDF(pc) (604KB) ( 214 )
Evolutions of defects and helium contained defects produced by atomic displacement and helium deposition with helium implantation at different temperatures in novel high silicon (NHS) steel are investigated by a slow positron beam. Differences of the defect information among samples implanted by helium to a fluence of 1×1017 ions/cm2 at room temperature, 300°C, 450°C and 750°C are discussed. It is found that the mobility of vacancies and vacancy clusters, a recombination of vacancy-type defects and the formation of the He-V complex lead to the occurrence of these differences. At high temperature irradiations, a change of the diffusion mechanism of He atoms/He bubbles might be one of the reasons for the change of the S-parameter.
Effect of Tin Incorporation on Thermo-Mechanical Properties of Glassy Se80Te20 Alloy
H. Kumar, A. Sharma, N. Mehta
Chin. Phys. Lett. 2014, 31 (03): 036201 .   DOI: 10.1088/0256-307X/31/3/036201
Abstract   PDF(pc) (454KB) ( 357 )
We report an analysis on the hardness behavior of glassy Se80?xTe20Snx alloy. The crucial thermo-mechanical parameters (micro-hardness, volume and formation energy of micro-voids and the modulus of elasticity) are examined. The results indicate that the thermo-mechanical parameters are changed significantly after incorporation of Sn in glassy Se80Te20 alloy.
The Electronic Structure and Formation Energies of Ni-doped CuAlO2 by Density Functional Theory Calculation
XU Ying, LI Fei, SHENG Wei, NIE Guo-Zheng, YUAN Ding-Wang
Chin. Phys. Lett. 2014, 31 (03): 037101 .   DOI: 10.1088/0256-307X/31/3/037101
Abstract   PDF(pc) (644KB) ( 627 )

The electronic structure and formation energies of Ni-doped CuAlO2 are calculated by first-principles calculations. Our results show that Ni is good for p-type doping in CuAlO2. When Ni is doped into CuAlO2, it prefers to substitute Al-site. NiAl is a shallow acceptor, while NiCu is a deep acceptor and its formation energy is high. Further electronic structure calculations show that strong hybridization happens between Ni-3d and O-2p states for Ni substituting Al-site, while localized Ni-3d states are found for Ni substituting Cu-site.

Effects of Carrier Gas on Carbon Incorporation in GaN
ZHANG Jian-Li, LIU Jun-Lin, PU Yong, FANG Wen-Qing, ZHANG Meng, JIANG Feng-Yi
Chin. Phys. Lett. 2014, 31 (03): 037102 .   DOI: 10.1088/0256-307X/31/3/037102
Abstract   PDF(pc) (408KB) ( 1022 )
GaN epitaxial layers were grown on Si (111) substrates by metal organic chemical vapor deposition. Carbon concentrations in the films grown in different ambients were measured by secondary ion mass spectrometry. The results show that the carbon incorporation is strongly dependent on the H2 flow rate when the NH3 flow rate is small, but insensitive to the H2 flow rate when the NH3 flow rate is sufficient large. We conclude that H2 can inhibit the dissociation of NH3 and result in a less active N source; an insufficiently active N source causes more N vacancies, which enhances carbon incorporation.
Effect of Mg and Fe Doping on Optical Absorption of LiNbO3 Crystal through First Principles Calculations
HUANG Duo-Hui, YANG Jun-Sheng, CAO Qi-Long, WAN Ming-Jie, LI Qiang, SUN Liang, WANG Fan-Hou
Chin. Phys. Lett. 2014, 31 (03): 037103 .   DOI: 10.1088/0256-307X/31/3/037103
Abstract   PDF(pc) (699KB) ( 484 )
Using first principles calculations, we investigate the structural, optical, and electronic properties of LiNbO3 (LN) and M doped LN (M=Mg, Fe). The density of states are calculated to analyze the effect of doping Mg and Fe ions on the absorption spectra and electronic properties of LN. The results show an ultraviolet shift in the optical absorption edge of Mg-doped LN compared with that of intrinsic LN. On the contrary, the absorption edge of Fe-doped LN crystal reveals a red shift. The optical absorption spectra show an improved optical response in the visible range for Mg-doped LN, which significantly differs from that obtained for Fe-doped LN. The electronic excitations from the valence band to the conduction band of LN leads to an improved optical absorption response in the visible region as observed experimentally. The obvious changes of the doped LN crystal are found in some cases, which provide a helpful guide for preparing doped LN crystal.
AlGaN/GaN HEMTs on 4-Inch Silicon Substrates in the Presence of 2.7-µm -Thick Epilayers with the Maximum Off-State Breakdown Voltage of 500 V
YU Xin-Xin, NI Jin-Yu, LI Zhong-Hui, KONG Cen, ZHOU Jian-Jun, DONG Xun, PAN Lei, KONG Yue-Chan, CHEN Tang-Sheng
Chin. Phys. Lett. 2014, 31 (03): 037201 .   DOI: 10.1088/0256-307X/31/3/037201
Abstract   PDF(pc) (691KB) ( 839 )

We report on the high breakdown performance of AlGaN/GaN high electron mobility transistors (HEMTs) grown on 4-inch silicon substrates. The HEMT structure including three Al-content step-graded AlGaN transition layers has a total thickness of 2.7 μm. The HEMT with a gate width WG of 300 μm acquires a maximum off-state breakdown voltage (BV) of 550 V and a maximum drain current of 527 mA/mm at a gate voltage of 2 V. It is found that BV is improved with the increase of gate-drain distance LGD until it exceeds 8 μm and then BV is tended to saturation. While the maximum drain current drops continuously with the increase of LGD. The HEMT with a WG of 3 mm and a LGD of 8 μm obtains an off-state BV of 500 V. Its maximum leakage current is just 13 μA when the drain voltage is below 400 V. The device exhibits a maximum output current of 1 A with a maximum transconductance of 242 mS.

Directional Plasmon Filtering in a Two-Dimensional Electron Gas Embedded in High-Index Crystallographic Planes
CHEN Jian, XU Huai-Zhe
Chin. Phys. Lett. 2014, 31 (03): 037301 .   DOI: 10.1088/0256-307X/31/3/037301
Abstract   PDF(pc) (651KB) ( 298 )
We study theoretically the plasmon excitations in a two-dimensional electron gas (2DEG) with spin-orbit interactions (SOIs) embedded in a (11n) crystallographic plane. We demonstrate that the energy spectra and dielectric functions between the 2DEGs embedded in different crystallographic planes can be related by a unitary transformation. Using the unitary transformation, we find that the anisotropy of plasmon excitations and the directional plasmon filtering (DPF) can be tuned by changing the strengths of SOIs in the high-index planes. There are two advantageous directions [110] and [nn2] for plasmon propagation. Moreover, the anisotropy and the DPF can be smeared out by tuning the strength ratio α/β between the Rashba SOI and the Dresselhaus SOI.
Trap States in Al2O3 InAlN/GaN Metal-Oxide-Semiconductor Structures by Frequency-Dependent Conductance Analysis
ZHANG Peng, ZHAO Sheng-Lei, XUE Jun-Shuai, ZHANG Kai, MA Xiao-Hua, ZHANG Jin-Cheng, HAO Yue
Chin. Phys. Lett. 2014, 31 (03): 037302 .   DOI: 10.1088/0256-307X/31/3/037302
Abstract   PDF(pc) (600KB) ( 614 )
We present a detailed analysis of the trap states in atomic layer deposition Al2O3/InAlN/GaN high electron mobility transistors grown by pulsed metal organic chemical vapor deposition. Trap densities, trap energies and time constants are determined by frequency-dependent conductance measurements. A high trap density of up to 1.6×1014 cm?2eV?1 is observed, which may be due to the lack of the cap layer causing the vulnerability to the subsequent high temperature annealing process.
Anomalous Dispersion Behavior of Staggered Arranged Metal Nanowire Arrays
CHEN Jun-Xue, SHANG Li-Ping
Chin. Phys. Lett. 2014, 31 (03): 037303 .   DOI: 10.1088/0256-307X/31/3/037303
Abstract   PDF(pc) (1879KB) ( 207 )
The dispersion relations of staggered arranged metal nanowire arrays are numerically investigated. It is demonstrated that the structure can support the propagation of plasmon modes with zero and negative group velocities derived directly from the dispersion curves, apart from normal plasmon modes with positive group velocities. Furthermore, the effects of the structural parameters on the dispersion behaviors of plasmon modes are also examined.
Effects of Thickness and Polarization Field on the Photovoltaic Properties of BiFeO3 Thin Films
ZHOU Yin-E, TAN Xin-Yu, YU Ben-Fang, LIU Li, YUAN Song-Liu, JIAO Wei-Hong
Chin. Phys. Lett. 2014, 31 (03): 037304 .   DOI: 10.1088/0256-307X/31/3/037304
Abstract   PDF(pc) (689KB) ( 484 )
We study the effects of film thickness on lattice parameters, direct band gap and photovoltaic outputs in the sol-gel derived BiFeO3 thin films. With the change of the film thickness, the great transitions will take place in the preferred orientation and lattice parameters. Furthermore, the photovoltaic outputs are significantly dependent on the film thickness. The results show that the open circuit voltage gradually increases and the short circuit current reciprocally decreases with the increase of film thickness. In particular, we demonstrate for the first time that there are tunable photovoltaic outputs with external electric field polarization switching in the polycrystalline BiFeO3 film, which is critical for the future device applications based on the photovoltaic properties of BiFeO3 films.
Tuning Out-of-Plane Spin Polarization Using in-Plane Magnetic Fields in a Quasi-One-Dimensional Quantum Wire Embedded in (110) Plane
SUN Jin-Fang, CHENG Fang
Chin. Phys. Lett. 2014, 31 (03): 037305 .   DOI: 10.1088/0256-307X/31/3/037305
Abstract   PDF(pc) (938KB) ( 206 )
We investigate theoretically the combination effect of an in-plane magnetic field and spin-orbit interactions (SOIs) on the spin and charge transport property of a quasi-one-dimensional quantum wire embedded in the (110) crystallographic plane. We find that the oscillations of the conductance induced by the SOIs become more significant and different for the spin-up and spin-down electrons in the presence of the in-plane magnetic field. The conductance exhibits a significant anisotropic behavior and electrons exhibit out-of-plane spin polarization which can be tuned by an in-plane magnetic field. These features offer us an efficient way to control SOI-induced spin transport using in-plane magnetic fields.
Probing Majorana Bound States in T-Shaped Junctions
WU Bin-He, CHENG Xiao, WANG Chun-Rui, GONG Wei-Jiang
Chin. Phys. Lett. 2014, 31 (03): 037306 .   DOI: 10.1088/0256-307X/31/3/037306
Abstract   PDF(pc) (592KB) ( 411 )

We investigate the transport properties of a pair of Majorana bound states in a T-shaped junction, where two normal leads are coupled with an identical Majorana bound state. Both the scattering matrix and the recursive Green function method show that the peak value of the differential conductance (Gpeak) in units of e2/h and the shot noise Fano factor in the zero bias limit (F0), which are measured at the same lead and zero temperature, satisfy a linear relation as F0=1+Gpeak/2, independent of the magnitude or symmetry of the coupling strengths to the leads. Therefore, combined measurements of the differential conductance and shot noise in the T-shaped geometry can serve as a characteristic signature in probing Majorana bound states.

Josephson Effect in Graphene: Comparison of Real and Pseudo Vector Potential Barriers
Tatnatchai Suwannasit, Rassmidara Hoonsawat, I-Ming Tang, Bumned Soodchomshom
Chin. Phys. Lett. 2014, 31 (03): 037401 .   DOI: 10.1088/0256-307X/31/3/037401
Abstract   PDF(pc) (756KB) ( 368 )
The Josephson currents through real vector potential (RVP) and pseudo vector potential (PVP) barriers in graphene are investigated. In graphene, the pseudo vector potential may be caused by a local strain. The comparison of supercurrents induced by the two type-barriers is focused. As a result, we find that not only will the RVP induce a transition Josephson current from the 0→π state but also causes the difference in the phases of the order parameters of the two superconducting graphene layers to shift from φ→2φ. The critical current is PVP-independent around the neutrality point while it strongly depends on the RVP. The vector potential dependence of critical current is found to be perfectly linear for both PVP and RVP barriers.
Effect of the O2/Ar Pressure Ratio on the Microstructure and Surface Morphology of Epi-MgO/IBAD-MgO Templates for GdBa2Cu3O7−δ Coated Conductors
LUO Qiang, LIU Lin-Fei, XIAO Gui-Na, LI Yi-Jie
Chin. Phys. Lett. 2014, 31 (03): 037402 .   DOI: 10.1088/0256-307X/31/3/037402
Abstract   PDF(pc) (1178KB) ( 243 )
High-quality epi-MgO buffer layers under different O2/Ar pressure ratios are fabricated by rf magnetron sputtering on textured IBAD-MgO templates. Under the total deposition pressure remaining constant (14 Pa), the effect of changing the ratio of O2/Ar pressure from 1:4 to 3:2 on the microstructure and surface morphology of epi-MgO films is studied. The microstructure and morphology of epi-MgO are fully characterized by x-ray diffraction, atom force microscope and scanning electron microscope. The best texture quality of epi-MgO with an out-plane Δω value of 1.8° and an in-plane Δ? value of 5.22° are obtained under the ratio of O2/Ar pressure 3:2. Further, the surface morphology indicates that the surface of epi-MgO is smooth with rms surface roughness about 4.7 nm at O2/Ar pressure ratio 3:2. After that, GdBa2Cu3O7 (GBCO) layers are deposited on the CeO2 cap layer buffered epi-MgO/IBAD-MgO templates to assess the efficiency of such a buffer layer stack. The critical current density of GBCO films (thickness of 200 nm) is higher than 3 MA/cm2, indicating that epi-MgO/IBAD-MgO is promising for depositing superconducting layers with a higher critical current density.
Calculation of Exchange Constants in Spinels Chromites ZnxCo1−xCr2O4
R. Masrour, M. Hamedoun, A. Benyoussef , E. K. Hlil, O. Mounkachi, H. El Moussaoui
Chin. Phys. Lett. 2014, 31 (03): 037501 .   DOI: 10.1088/0256-307X/31/3/037501
Abstract   PDF(pc) (511KB) ( 422 )

The exchange interactions of the nearest-neighbor exchange constant between tetrahedral and octahedral sublattices (JAB(x)), nearest-neighbor exchange constant inside tetrahedral sublattice (JAA(x)) and nearest-neighbor exchange constant inside octahedral sublattice (JBB(x)) in cobalt and zinc chromites are calculated using the probability distribution. The Curie–Weiss temperature and the critical temperature are deduced using the mean field and the high temperature series expansion theories in ZnxCo1−xCr2O4. The critical exponent associated with the magnetic susceptibility (γ) is deduced for CoCr2O4.

Fabrication of Micro-Grooves in Silicon Carbide Using Femtosecond Laser Irradiation and Acid Etching
KHUAT Vanthanh, MA Yun-Can, SI Jin-Hai, CHEN Tao, CHEN Feng, HOU Xun
Chin. Phys. Lett. 2014, 31 (03): 037901 .   DOI: 10.1088/0256-307X/31/3/037901
Abstract   PDF(pc) (874KB) ( 281 )
A simple method using an 800-nm femtosecond laser and chemical selective etching is developed for fabrication of high-aspect-ratio grooves in silicon carbide. Micro grooves with an aspect ratio of approximately 40 are obtained. The morphology and chemical compositions of the grooves are analyzed using a scanning electronic microscope equipped with an energy dispersive x-ray spectroscopy. The formation mechanism of SiC grooves is attributed to the chemical reactions of the laser induced structural changes with a mixed solution of hydrofluoric acid and nitric acid. In addition, the effects of laser irradiation parameters on the aspect ratio of the grooves are investigated.
Heterogeneous Nucleation on a Conical Cavity
LI Xiang-Ming
Chin. Phys. Lett. 2014, 31 (03): 038201 .   DOI: 10.1088/0256-307X/31/3/038201
Abstract   PDF(pc) (529KB) ( 506 )
Heterogeneous nucleation in a conically shaped pit on the surface of a plane surface substrate is investigated. The growing process of a cluster on the substrate consists of three stages: growing within the conical cavity, at the cavity edge and outside the cavity. In every stage, the thermodynamic criterion of a cluster growing into a nucleus depends on both the conical cavity dimensions and the substrate materials. The free energy barrier for nucleus formation and the condition of twice nucleation are obtained.
Simulation and Experimentation for Low Density Drain AlGaN/GaN HEMT
WANG Chong, HE Yun-Long, DING Ning, ZHENG Xue-Feng, ZHANG Peng, MA Xiao-Hua, ZHANG Jin-Cheng, HAO Yue
Chin. Phys. Lett. 2014, 31 (03): 038501 .   DOI: 10.1088/0256-307X/31/3/038501
Abstract   PDF(pc) (1118KB) ( 358 )
In order to improve the breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs), we report a feasible method of low density drain (LDD) HEMT. The fluoride-based plasma treatment using CF4 gas is performed on the drain-side of the gate edge. The channel two-dimensional electron gas (2DEG) concentrations are modulated by fluoride plasma treatment, and the peak electric field at the gate edge is effectively reduced, so the breakdown voltage is improved. The electric field distributions of the LDD-HEMTs are simulated using the Silvaco software, and the peak of the electric field on the gate edge is effectively reduced. Experimental results show that, compared with the conventional HEMT, LDD-HEMTs have a lower reverse leakage current of the gate, and the breakdown voltage is increased by 36%. The current collapse characteristics of the LDD-HEMTs are confirmed by dual-pulse measurement, and an obvious pulse current reduction is due to the surface states by implanting F ions between the gate and the drain.
Calculation of the Physical and Microdosimetric Parameters of Electron and Alpha-Particle Radiation Using Monte Carlo Simulations
GENG Jin-Peng, CAO Tian-Guang, LI Duo-Fang, AN Hai-Long, HAN Ying-Rong, LI Jin, HU Jin-Shan, LI Nan-Nan, ZHAN Yong
Chin. Phys. Lett. 2014, 31 (03): 038701 .   DOI: 10.1088/0256-307X/31/3/038701
Abstract   PDF(pc) (583KB) ( 297 )
Various ionizing radiations, such as electrons and alpha particles, transfer their energy to media by produced secondary electrons and induce double- or single-strand break of DNA, which result in variable effects. To understand how the ionizing radiations interact with DNA and break it, several models have been developed, most of them consider the water as a vapor state. Actually, the ionizing particles interact with DNA which is solved in liquid water. To compare the difference of vapor and liquid water models, we calculate the stopping power, continuous slowing down approximation (CSDA) range and S value of electrons and alpha particles at cellular scale in liquid and vapor by Monte Carlo simulations, respectively. Our data show that the stopping power and CSDA range are different in liquid and vapor water in a special energy range. For many S values, the liquid model is better than the vapor model when the energy of the electrons is higher than 100 keV and the vapor model is higher than the liquid model for the 1 MeV alpha particles.
An Improved Model of the Jovian Magnetosphere
LU Bin, CHEN Chu-Xin
Chin. Phys. Lett. 2014, 31 (03): 039601 .   DOI: 10.1088/0256-307X/31/3/039601
Abstract   PDF(pc) (436KB) ( 963 )
The Jovian magnetosphere is modulated by the solar wind and centrifugal force. The configuration of the magnetic field in the previous model of the magnetosphere including the centrifugal force is consistent with the observations at low magnetic latitude (Λ<50°), while there is a substantial difference between the results of the model and the observations at high magnetic latitude (Λ≥50°), especially in the distant magnetotail. Based on the previous model, a new configuration of the Jovian magnetosphere in the night side is suggested by a three-step transformation in this study. The new magnetosphere obtained by the transformation method is flattened in the z-direction and stretched in the x-direction in distant magnetotail, which agree with general knowledge.
47 articles