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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2015, 32 (3)   Published: 26 February 2015
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GENERAL

Minimal Length Quantum Mechanics of Dirac Particles in Noncommutative Space

A. N. Ikot, H. P. Obong, H. Hassanabadi
Chin. Phys. Lett. 2015, 32 (3): 030201 doi: 10.1088/0256-307X/32/3/030201
Full Text: [PDF 479 KB] (22)
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We study the two-dimensional harmonic oscillator in commutative and noncommutative space within the framework of minimal length quantum mechanics for spin-1/2 particles. The energy spectra and the eigenfunction are obtained in both cases. Special cases are also deduced.

A Phenomenon of Decoherence Induced by Chaotic Environment

YANG Yin-Biao, WANG Wen-Ge
Chin. Phys. Lett. 2015, 32 (3): 030301 doi: 10.1088/0256-307X/32/3/030301
Full Text: [PDF 569 KB] (17)
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By means of numerical simulation, we reveal a phenomenon which is due to decoherence induced by chaotic motion of a large environment. We study the possibility of replacing the environmental components of the state vector of the total system by some randomly-chosen vectors in the Hilbert space of the environment when decoherence has happened. It is shown that, in the future evolution, the reduced density matrices obtained in this way are quite close to those computed from the exact, continuous Schrödinger evolution of the total system. Similar results are also found in the case that the Hamiltonian is changed at the time of replacing components.

Notes on Phase Transition of Nonsingular Black Hole

MA Meng-Sen, ZHAO Ren
Chin. Phys. Lett. 2015, 32 (3): 030401 doi: 10.1088/0256-307X/32/3/030401
Full Text: [PDF 427 KB] (6)
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On the belief that a black hole is a thermodynamic system, we study the phase transition of nonsingular black holes. If the black hole entropy takes the form of the Bekenstein–Hawking area law, the black hole mass M is no longer the internal energy of the black hole thermodynamic system. Using the thermodynamic quantities, we calculate the heat capacity, thermodynamic curvature and free energy. It is shown that there will be a larger black hole/smaller black hole phase transition for the nonsingular black hole. At the critical point, the second-order phase transition appears.

Efficiency-Controllable Random Walks on a Class of Recursive Scale-Free Trees with a Deep Trap

LI Ling, GUAN Ji-Hong, ZHOU Shui-Geng
Chin. Phys. Lett. 2015, 32 (3): 030501 doi: 10.1088/0256-307X/32/3/030501
Full Text: [PDF 466 KB] (7)
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Controls, especially efficiency controls on dynamical processes, have become major challenges in many complex systems. We study an important dynamical process, random walk, due to its wide range of applications for modeling the transporting or searching process. For lack of control methods for random walks in various structures, a control technique is presented for a class of weighted treelike scale-free networks with a deep trap at a hub node. The weighted networks are obtained from original models by introducing a weight parameter. We compute analytically the mean first passage time (MFPT) as an indicator for quantitatively measuring the efficiency of the random walk process. The results show that the MFPT increases exponentially with the network size, and the exponent varies with the weight parameter. The MFPT, therefore, can be controlled by the weight parameter to behave superlinearly, linearly, or sublinearly with the system size. This work provides further useful insights into controlling efficiency in scale-free complex networks.

Synchronization Dynamics in a System of Multiple Interacting Populations of Phase Oscillators

JU Ping, YANG Jun-Zhong
Chin. Phys. Lett. 2015, 32 (3): 030502 doi: 10.1088/0256-307X/32/3/030502
Full Text: [PDF 1221 KB] (9)
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We study the synchronization dynamics in a system of multiple interacting populations of phase oscillators. Using the dimensionality-reduction technique of Ott and Antonsen, we explore different types of synchronization dynamics when the incoherent state becomes unstable. We find that the inter-population coupling is crucial to the synchronization. When the intra-population interaction is repulsive, the local synchronization can still be maintained through the inter-population coupling. For attractive inter-population coupling, the local order parameters in different populations are of in-phase while the local synchronization are of anti-phase for repulsive inter-population coupling.

Circuit Implementations, Bifurcations and Chaos of a Novel Fractional-Order Dynamical System

MIN Fu-Hong, SHAO Shu-Yi, HUANG Wen-Di, WANG En-Rong
Chin. Phys. Lett. 2015, 32 (3): 030503 doi: 10.1088/0256-307X/32/3/030503
Full Text: [PDF 1130 KB] (15)
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Linear transfer function approximations of the fractional integrators 1/sm with m=0.80–0.99 with steps of 0.01 are calculated systemically from the fractional order calculus and frequency−domain approximation method. To illustrate the effectiveness for fractional functions, the magnitude Bode diagrams of the actual and approximate transfer functions 1/sm with a slope of -20m dB/decade are depicted. By using the transfer function approximations of the fractional integrators, a new fractional-order nonlinear system is investigated through the bifurcation diagram and Lyapunov exponent. The corresponding circuit of the fractional-order system is designed and the experimental results match perfectly with the numerical simulations.

An FPGA-Based Pulse Pile-up Rejection Technique for Photon Counting Imaging Detectors

HU Kun, LI Feng, CHEN Lian, LIANG Fu-Tian, JIN Ge
Chin. Phys. Lett. 2015, 32 (3): 030701 doi: 10.1088/0256-307X/32/3/030701
Full Text: [PDF 622 KB] (10)
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A novel FPGA-based pulse pile-up rejection method for single photon imaging detectors is reported. The method is easy to implement in FPGAs for real-time data processing. The rejection principle and entire design are introduced in detail. The photon counting imaging detector comprises a micro-channel plate (MCP) stack, and a wedge and strip anode (WSA). The resolution mask pattern in front of the MCP can be reconstructed after data processing in the FPGA. For high count rates, the rejection design can effectively reduce the impact of the pulse pile-up on the image. The resolution can reach up to 140 μm. The pulse pile-up rejection design can also be applied to high-energy physics and particle detection.
NUCLEAR PHYSICS

Comparison of Experiment and Simulation of the triple GEM-Based Fast Neutron Detector

WANG Xiao-Dong, ZHANG Jun-Wei, HU Bi-Tao, YANG He-Run, DUAN Li-Min, LU Chen-Gui, HU Rong-Jiang, ZHANG Chun-Hui, ZHOU Jian-Rong, YANG Lei, AN Lv-Xing, LUO Wen
Chin. Phys. Lett. 2015, 32 (3): 032901 doi: 10.1088/0256-307X/32/3/032901
Full Text: [PDF 565 KB] (6)
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neutrons based on a 10×10 cm2 triple gas electron multiplier (GEM) device is developed and tested. A neutron converter, which is a high density polyethylene (HDPE) layer, is combined with the triple GEM detector cathode and placed inside the detector, in the path of the incident neutrons. The detector is tested by obtaining the energy deposition spectrum with an Am Be neutron source in the Institute of Modern Physics (IMP) at Lanzhou. In the present work we report the results of the tests and compare them with those of simulations. The transport of fast neutrons and their interactions with the different materials in the detector are simulated with the GEANT4 code, to understand the experimental results. The detector displays a clear response to the incident fast neutrons. However, an unexpected disagreement in the energy dependence of the response between the simulated and measured spectra is observed. The neutron sources used in our simulation include deuterium-tritium (DT, 14 MeV), deuterium-deuterium (DD, 2.45 MeV), and Am Be sources. The simulation results also show that among the secondary particles generated by the incident neutron, the main contributions to the total energy deposition are from recoil protons induced in hydrogen-rich HDPE or Kapton (GEM material), and activation photons induced by neutron interaction with Ar atoms. Their contributions account for 90% of the total energy deposition. In addition, the dependence of neutron deposited energy spectrum on the composition of the gas mixture is presented.
ATOMIC AND MOLECULAR PHYSICS

Magic Wavelengths of the Optical Clock Transition at 1107 nm of Barium

YU Geng-Hua, XU Qi-Ming, ZHOU Chao, DUAN Cheng-Bo, LI Long, CHAI Rui-Peng
Chin. Phys. Lett. 2015, 32 (3): 033201 doi: 10.1088/0256-307X/32/3/033201
Full Text: [PDF 696 KB] (13)
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Magic wavelengths for laser trapping of barium atoms in the optical lattices are calculated with considering the optical clock transition at 1107 nm between the 6s2 1S0 state and 6s5d 3D1 state. Theoretical calculation shows that there are several magic wavelengths with the linearly polarized trapping laser. The trap depths of the optical lattice and the slope of light shift difference with different magic wavelengths are also calculated. Some of these magic wavelengths are selected and recommended as potentially suitable magic wavelengths for the optical lattice trapping laser.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

Radiation of Ultra Low Frequency Electromagnetic Waves from Atmosphere under the Influence of Strong Shock Waves

A. R. Aramyan, S. A. Aramyan, S. G. Bilén, L. Sh. Grigoryan, H. F. Khachatryan
Chin. Phys. Lett. 2015, 32 (3): 034101 doi: 10.1088/0256-307X/32/3/034101
Full Text: [PDF 678 KB] (7)
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We present preliminary results from the experimental investigation of the response of the atmosphere due to the impact of powerful shock waves. The response is evidenced as ultra low frequency electromagnetic wave radiation at frequency of 2–5 kHz and in duration of 3–7 s. We hypothesize that this radiation appears due to the following process: the shock wave ionizes the neutral particles in the air and these charged and neutral particles continue their vertical motion, which forms in the trail of the shock wave. Such motion can cause the cyclotron-like radiation measured.

Intensity Distributions of a Supercontinuum Laser in an Apertured Dispersion Lens

YUAN Na, ZHANG Wei, WANG Juan, CHEN Wei, PENG Run-Wu
Chin. Phys. Lett. 2015, 32 (3): 034201 doi: 10.1088/0256-307X/32/3/034201
Full Text: [PDF 439 KB] (5)
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We present intensity distributions of a supercontinuum laser passing through an apertured dispersion lens and find focal shift effects generated. The results show that, apart from the conventional negative focal shift, a positive focal shift also appears in the supercontinuum laser. The maximum intensity of the supercontinuum laser shifts toward the lens when the truncated parameter is small. However, it exceeds the focus of the central wavelength and a positive focal shift appears in the supercontinuum laser with large truncated parameter. Both of the maximum intensities shift away from the focus when the bandwidth of the supercontinuum laser increases, while the shift direction is opposite. No focal shift appears when the bandwidth and the truncated parameter satisfy some conditions.

Liquid Concentration Sensing Properties of Microfibers with a Nanoscale-Structured Film

ZHOU Guo-Rui, LV Hai-Bing, YUAN Xiao-Dong, ZHOU Hai, LIU Hao, LI Ke-Xin, CHENG Xiao-Feng, MIAO Xin-Xiang
Chin. Phys. Lett. 2015, 32 (3): 034202 doi: 10.1088/0256-307X/32/3/034202
Full Text: [PDF 945 KB] (4)
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A type of compact solution concentration sensor based on a microfiber with a nanoscale-structured film is proposed and demonstrated experimentally. Additional loss at different solution concentrations is calculated by means of the three-dimensional finite-difference time-domain (3D-FDTD) method. The microfiber is fabricated by using the flame-heated scanning technique. Nanoscale-structured film is coated on the microfiber surface, which is assembled as a sensing unit. The sensitivity of this kind of sensor increases with the decreasing diameters of the microfiber. When the diameter of the microfiber is 2 μm, a minimum concentration sensitivity of 1% (under 450 s measuring time) is demonstrated in the experiment. Higher sensitivity can be attained when the solution concentration is higher. The sensing properties of this microfiber with the nanoscale-structured film may provide opportunities for new applications in optical sensing devices.

Harmonic Dark Pulse Emission in Erbium-Doped Fiber Laser

Zian Cheak Tiu, Arman Zarei, Sin Jin Tan, Harith Ahmad, Sulaiman Wadi Harun
Chin. Phys. Lett. 2015, 32 (3): 034203 doi: 10.1088/0256-307X/32/3/034203
Full Text: [PDF 454 KB] (8)
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A harmonic dark pulse generation in an erbium-doped fiber laser is demonstrated based on a figure-of-eight configuration. It is found that the harmonic dark pulse can be shifted from the fundamental to the 5th order harmonic by increasing the pump power with an appropriate polarization controller orientation. The fundamental repetition rate of 20 kHz is obtained at the pump power of 29 mW. The highest pulse energy of 42.6 nJ is obtained at the fundamental repetition rate. The operating frequency of the dark pulse trains shifts to 2nd, 3rd, 4th and 5th harmonic as the pump powers are increased to 34 mW, 50 mW, 59 mW and 137 mW, respectively.

Fabrication of Tm-Doped Fibers for High Power and 121 W Output All-Fiber Tm-Doped Fiber Laser

XING Ying-Bin, LIAO Lei, BU Fan, WANG Yi-Bo, PENG Jing-Gang, DAI Neng-Li, LI Jin-Yan
Chin. Phys. Lett. 2015, 32 (3): 034204 doi: 10.1088/0256-307X/32/3/034204
Full Text: [PDF 1425 KB] (4)
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We fabricate the Tm-doped double cladding silica fiber by using the vapor-solution hybrid-doping method, then build up an all-fiber Tm-doped fiber laser which can provide the output power of up to 121 W, corresponding to a slope efficiency of 51% and an optical-optical efficiency of 48%. By using the domestic Tm-doped fiber, it is the first time a hundred-watt level output at 1915 nm has been achieved, to the best of our knowledge. The thermal effect of Tm-doped fiber laser is also analyzed.

Power-Dependent Luminescence of CdSe/ZnS Nanocrystal Assembled Layer-by-Layer on a Silver Nanorod Array

WANG Ya-Lan, CHENG Zi-Qiang, MA Liang, PENG Xiao-Niu, HAO Zhong-Hua, WANG Qu-Quan
Chin. Phys. Lett. 2015, 32 (3): 034205 doi: 10.1088/0256-307X/32/3/034205
Full Text: [PDF 745 KB] (8)
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We investigate the power-dependent luminescence of CdSe/ZnS semiconductor quantum dots closely packed layer-by-layer in the proximity of a silver nanorod array cavity. It is found that the emission peak shifts significantly to the longer wavelengths as the excitation power increases, especially when the longitudinal surface plasmon resonance of the Ag nanorod array cavity is adjusted to be close to the emission wavelength. The equivalent gain varies with the coating layer of CdSe/ZnS semiconductor quantum dots and the excitation power is also studied to explain this interesting spectrum-shifting effect. These findings could find applications in the dynamic information processing of active plasmonic and photonic nanodevices.

Diode-Pumped c-Cut Nd:Lu0.99La0.01VO4 Self-Stimulated Raman Laser at 1181 nm

CAI Wei-Yang, DUAN Yan-Min, LI Jiang-Tao, YAN Lin-Fei, MAO Meng-Jiao, ZHAO Bin, ZHU Hai-Yong
Chin. Phys. Lett. 2015, 32 (3): 034206 doi: 10.1088/0256-307X/32/3/034206
Full Text: [PDF 657 KB] (5)
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The self-stimulated Raman laser operation of a Nd:Lu0.99La0.01VO4 new crystal is presented. A 0.3 at.% Nd doped Lu0.99La0.01VO4 crystal in dimensions 3×3×20 mm3 is adopted as the self-stimulated Raman crystal. At a pulse repetition frequency of 14 kHz, average output powers of 240 mW for the first Stokes light at 1181 nm and 660 mW for the fundamental light at 1068 nm are obtained under an incident pump power of 5.5 W. The pulse widths of the first Stokes light and fundamental light are about 15 and 25 ns. The slope efficiencies are about 12.7% and 18.8% with respect to the incident pump power.

Research on Vibration Mechanism of Plant Cell Membrane with Ultrasonic Irradiation

CAO Hui, HUANG Wan-Jun, QIAO Jia-Ting, WANG Yun-Peng, ZHAO Hai-Jun
Chin. Phys. Lett. 2015, 32 (3): 034301 doi: 10.1088/0256-307X/32/3/034301
Full Text: [PDF 509 KB] (7)
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The vibration mechanism of the cell membrane of plant seeds is analyzed based on the physical effect of ultrasound. The vibration model of cell rectangular membrane of plant seeds is then proposed and the expression of resonance frequency is obtained. The resonance frequency of cell membrane under the built model in the case of knowing the surface tension, surface density and size of cell membrane are calculated. The results of the theoretical calculations are in accordance with the previous experimental results. The built vibration model of cell membrane has certain rationality and certain reference significance to the determination of parameters in ultrasonic breeding in physical agriculture.

Numerical Simulation of Shock Bubble Interaction with Different Mach Numbers

YANG Jie, WAN Zhen-Hua, WANG Bo-Fu, SUN De-Jun
Chin. Phys. Lett. 2015, 32 (3): 034701 doi: 10.1088/0256-307X/32/3/034701
Full Text: [PDF 681 KB] (4)
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The interaction of a shock wave with a spherical helium bubble is investigated numerically by using the high-resolution piecewise parabolic method (PPM), in which the viscous and turbulence effects are both considered. The bubble is of the same size and is accelerated by a planar shock of different Mach numbers (Ma). The results of low Ma cases agree quantitatively with those of experiments [G. Layes, O. Le Métayer, Phys. Fluids 19 (2007) 042105]. With the increase of Ma, the final geometry of the bubble becomes quite different, the compression ratio is highly raised, and the time-dependent mean bubble velocity is also influenced. The compression ratios measured can be well normalized when Ma is low, while less agreement has been achieved for high Ma cases. In addition, the mixedness between two fluids is enhanced greatly as Ma increases. Some existed scaling laws of these quantities for the shock wave strength cannot be directly applied to high Ma cases.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Anomalous Convection Reversal due to Turbulence Transition in Tokamak Plasmas

SUN Tian-Tian, CHEN Shao-Yong, WANG Zhan-Hui, PENG Xiao-Dong, HUANG Jie, MOU Mao-Lin, TANG Chang-Jian
Chin. Phys. Lett. 2015, 32 (3): 035201 doi: 10.1088/0256-307X/32/3/035201
Full Text: [PDF 1223 KB] (1)
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A critical physical model, based on the ion temperature gradient (ITG) mode and the trapped electron mode (TEM), trying to explain the spatio-temporal dynamics of anomalous particle convection reversal (i.e., the particle convective flux reverses from inward to outward), is developed numerically. The dependence of density peaking and profile shape on the particle convection is studied. Only the inward pinch could lead to the increase of the density peaking. The validation of the critical model is also analyzed. A comparison of the estimates calculated by the model and the experimental results from the Tore Supra tokamak shows that they are qualitatively both consistent.

Effect of Wave Accessibility on Lower Hybrid Wave Current Drive in Experimental Advanced Superconductor Tokamak with H-Mode Operation

LI Xin-Xia, XIANG Nong, GAN Chun-Yun
Chin. Phys. Lett. 2015, 32 (3): 035202 doi: 10.1088/0256-307X/32/3/035202
Full Text: [PDF 752 KB] (3)
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The effect of the wave accessibility condition on the lower hybrid current drive in the experimental advanced superconductor Tokamak (EAST) plasma with H-mode operation is studied. Based on a simplified model, a mode conversion layer of the lower hybrid wave between the fast wave branch and the slow wave branch is proved to exist in the plasma periphery for typical EAST H-mode parameters. Under the framework of the lower hybrid wave simulation code (LSC), the wave ray trajectory and the associated current drive are calculated numerically. The results show that the wave accessibility condition plays an important role on the lower hybrid current drive in EAST plasma. For wave rays with parallel refractive index n||=2.1 or n||=2.5 launched from the outside midplane, the wave rays may penetrate the core plasma due to the toroidal geometry effect, while numerous reflections of the wave ray trajectories in the plasma periphery occur. However, low current drive efficiency is obtained. Meanwhile, the wave accessibility condition is improved if a higher confined magnetic field is applied. The simulation results show that for plasma parameters under present EAST H-mode operation, a significant lower hybrid wave current drive could be obtained for the wave spectrum with peak value n||=2.1 if a toroidal magnetic field BT=2.5 T is applied.

Characterization of Femtosecond Laser-Induced Plasma under Low Pressure in Argon

CAO Yu, LIU Xiao-Liang, XIAN Wen-Duo, SUN Shao-Hua, SUN Ming-Ze, DING Peng-Ji, SHI Yan-Chao, LIU Zuo-Ye, HU Bi-Tao
Chin. Phys. Lett. 2015, 32 (3): 035203 doi: 10.1088/0256-307X/32/3/035203
Full Text: [PDF 885 KB] (3)
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An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and Ar ions. The lifetimes and characteristics of the Ar plasma are extensively studied by the time-integrated and time-resolved optical emission spectroscopy technique, which is also discussed. Under the assumption of local thermodynamic equilibrium (LTE), the plasma temperature is calculated. Moreover, the electron density is accessed from the Stark broadening of the ionized argon lines. Finally, the validity of applications of LTE is also discussed.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Stability and Electronic Properties of Hydrogenated Zigzag Carbon Nanotube Focused on Stone–Wales Defect

PAN Li-Jun, ZHANG Jie, CHEN Wei-Guang, TANG Ya-Nan
Chin. Phys. Lett. 2015, 32 (3): 036101 doi: 10.1088/0256-307X/32/3/036101
Full Text: [PDF 783 KB] (1)
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We present a first-principles study of the chemisorption of hydrogen on a Stone–Wales (SW) defective carbon nanotube (10,0). The investigated configurations include four configurations covering single defects and double defects. One hydrogen dimer adsorption is energetically favored on bonds shared by carbon heptagon-heptagon for configurations with the defect parallel to the tube axis compared with the carbon pentagon-hexagon sites for ones with a slanted defect. This different behavior is also demonstrated for hydrogen dimer chain adsorption, the favored site for the former ones is through the defect, which is the nearest neighbor site to defect for the latter ones. It is found that the energy band gaps of hydrogenated configurations may be enlarged or decreased by altering the adsorption site or defect position. The semiconductor-to-metal transition may occur for configurations with the defect or defects parallel to the tube axis due to low electronic localization. Our results highlight the interest of the interaction of multi-factor system by providing a detailed bond and position picture of a hydrogenated defective carbon nanotube (10,0).

Quasilattice-Conserved Optimization of the Atomic Structure of Decagonal Al-Co-Ni Quasicrystals

LI Xiao-Tian, YANG Xiao-Bao, ZHAO Yu-Jun
Chin. Phys. Lett. 2015, 32 (3): 036102 doi: 10.1088/0256-307X/32/3/036102
Full Text: [PDF 1087 KB] (1)
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The detailed atomic structure of quasicrystals has been an open problem for decades. Here we present a quasilattice-conserved optimization method (quasi-OPT), under particular quasiperiodic boundary conditions. As the atomic coordinates are described by basic cells and quasilattices, we are able to maintain the self-similarity characteristics of qusicrystals with the atomic structure of the boundary region updated timely following the relaxing region. Exemplified with the study of decagonal Al-Co-Ni (d-Al-Co-Ni), we propose a more stable atomic structure model based on Penrose quasilattice and our quasi-OPT simulations. In particular, rectangle-triangle rules are suggested for the local atomic structures of d-Al-Co-Ni quasicrystals.

The Structural, Dielectric, Lattice Dynamical and Thermodynamic Properties of Zinc-Blende CdX (X= S, Se, Te) from First-Principles Analysis

FENG Shi-Quan, LI Jun-Yu, CHENG Xin-Lu
Chin. Phys. Lett. 2015, 32 (3): 036301 doi: 10.1088/0256-307X/32/3/036301
Full Text: [PDF 830 KB] (1)
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The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX (X=S, Se, Te) are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the published experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal optical-transverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX (X= S, Se, Te) are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX (X= S, Se, Te) and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat Cv. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R.

Relaxation of 6H-SiC (0001) Surface and Si Adsorption on 6H-SiC (0001): an ab initio Study

HE Xiao-Min, CHEN Zhi-Ming, LI Lian-Bi
Chin. Phys. Lett. 2015, 32 (3): 036801 doi: 10.1088/0256-307X/32/3/036801
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First-principles calculations are carried out to study the relaxation of 6H-SiC (0001) surface and chemisorption models of Si adatoms on four high-symmetry adsorption sites. The surface results show that Si-termination is the preferred termination of the 6H-SiC(0001) polar surface and is more stable than the C-terminated 6H-SiC(0001) polar surface over a wide range of allowed chemical potentials. Four stable atomic configurations (top, bridge, hcp and fcc) are considered, and the adsorption energies and geometries, Mulliken charge population, and partial density of state (PDOS) properties are analyzed. Adsorption energy results show that the top site is the most stable site. The structural properties of Si adsorption on the SiC (0001) surface shows that increasing stability means decreasing bond lengths. Charge populations analysis and PDOS results imply that there is strong interaction between Si adatoms and 6H-SiC (0001) surface.

Electronic Structures and Adsorption of Li-Doped Graphenes for CO

LIU Xiao-Juan, CAO Wen-Qiang, HUANG Zi-Han, YUAN Jie, FANG Xiao-Yong, CAO Mao-Sheng
Chin. Phys. Lett. 2015, 32 (3): 036802 doi: 10.1088/0256-307X/32/3/036802
Full Text: [PDF 832 KB] (1)
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We research the adsorption geometries and electronic structures of pristine graphene (p−GR) and Li−doped graphene (Li-GR) before and after CO adsorption by first-principles. The adsorption energies Ead of CO on p-GR and Li-GR are calculated. The results demonstrate that Ead of CO on Li-GR is from -3.3 eV to -3.5 eV, meanwhile Q is up to 0.13 e, which indicate that strong electrostatic attractions occur between CO and Li-GR, while CO is physically adsorbed on p-GR. The obvious accumulated charge in electron density difference and increasing carrier density suggest that the conductivity of Li-GR is improved considerably after CO adsorption. An adsorption mechanism is also proposed. Our results provide a path to achieving CO sensors with high performance.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Density Functional Theory of Composite Fermions

ZHANG Yin-Han, SHI Jun-Ren
Chin. Phys. Lett. 2015, 32 (3): 037101 doi: 10.1088/0256-307X/32/3/037101
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We construct a density functional theory for two-dimensional electron (hole) gases subjected to both strong magnetic fields and external potentials. In particular, we are focused on regimes near even-denominator filling factors, in which the systems form composite fermion liquids. Our theory provides a systematic and rigorous approach to determine the properties of ground states in a fractional quantum Hall regime that is modified by artificial structures. We also propose a practical way to construct an approximated functional.

Ideal Strengths and Bonding Properties of UO2 under Tension

LI Li, WANG Bao-Tian, ZHANG Ping
Chin. Phys. Lett. 2015, 32 (3): 037102 doi: 10.1088/0256-307X/32/3/037102
Full Text: [PDF 759 KB] (1)
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By performing density functional theory plus U calculations, we systematically study the structural, electronic, and magnetic properties of UO2 under uniaxial tensile strain. The results show that the ideal tensile strengths along the [100], [110], and [111] directions are 93.6, 27.7, and 16.4 GPa at strains of 0.44, 0.24, and 0.16, respectively. After electronic-structure investigation for tensile stain along the [001] direction, we find that the strong mixed ionic/covalent character of U–O bond is weakened by the tensile strain and there will occur an insulator to metal transition at strain over 0.30.

Enhancement of Thermoelectric Performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 Ceramics by A-Site Cation Nonstoichiometry

ZHANG Xin, LIU Jian, LI Yi, SU Wen-Bin, LI Ji-Chao, ZHU Yuan-Hu, LI Mao-Kui, WANG Chun-Ming, WANG Chun-Lei
Chin. Phys. Lett. 2015, 32 (3): 037201 doi: 10.1088/0256-307X/32/3/037201
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Sr0.9Ba0.1−xTi0.8Nb0.2O3 ceramics (x=0, 0.01, 0.02 and 0.05) are prepared by solid state reaction, whose thermoelectric properties are investigated from 323 K to 1073 K. By introducing A-site nonstoichiometry, the absolute Seebeck coefficient is enhanced, while the electrical resistivity is surprisingly reduced due to the significantly enhanced carrier mobility. These results are dramatic in thermoelectric materials, effectively enhancing the power factor. Moreover, the thermal conductivity is reduced, thus the thermoelectric performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramic is significantly enhanced by A-site nonstoichiometry.

High-Temperature Performance Analysis of AlGaN/GaN Polarization Doped Field Effect Transistors Based on the Quasi-Multi-Channel Model

FANG Yu-Long, FENG Zhi-Hong, LI Cheng-Ming, SONG Xu-Bo, YIN Jia-Yun, ZHOU Xing-Ye, WANG Yuan-Gang, LV Yuan-Jie, CAI Shu-Jun
Chin. Phys. Lett. 2015, 32 (3): 037202 doi: 10.1088/0256-307X/32/3/037202
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We report on the temperature-dependent dc performance of AlGaN/GaN polarization doped field effect transistors (PolFETs). The rough decrements of drain current and transconductance with the operation temperature are observed. Compared with the conventional HFETs, the drain current drop of the PolFET is smaller. The transconductance drop of PolFETs at different gate biases shows different temperature dependences. From the aspect of the unique carrier behaviors of graded AlGaN/GaN heterostructure, we propose a quasi-multi-channel model to investigate the physics behind the temperature-dependent performance of AlGaN/GaN PolFETs.

High-Performance In0.23Ga0.77As Channel MOSFETs with High Current Ratio Ion/Ioff Grown on Semi-insulating GaAs Substrates by MOCVD

KONG Xiang-Ting, ZHOU Xu-Liang, LI Shi-Yan, QIAO Li-Jun, LIU Hong-Gang, WANG Wei, PAN Jiao-Qing
Chin. Phys. Lett. 2015, 32 (3): 037301 doi: 10.1088/0256-307X/32/3/037301
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We demonstrate high-performance In0.23Ga0.77As channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with Ion/Ioffhigh on-current to off-current (Ion/Ioff) ratio grown on semi-insulating GaAs wafers by metal-organic chemical vapor deposition (MOCVD). The 2 μm channel-length devices exhibit a peak extrinsic transconductance of 150 mS/mm and a drain current up to 500 mA/mm. The maximum effective mobility is 1680 cm2/Vs extracted by the split CV method. Furthermore, the Ion/Ioff ratio is significantly improved from approximately 4.5×103 up to approximately 4.32×104 by controlling the etch thickness of In0.49Ga0.51P. The high drain current and high Ion/Ioff ratio of the In0.23Ga0.77As channel MOSFETs are achieved due to the high effective mobility and the low gate leakage current density.

Variable Coupling Strength of Silicene on Ag(111)

FENG Bao-Jie, LI Wen-Bin, QIU Jing-Lan, CHENG Peng, CHEN Lan, WU Ke-Hui
Chin. Phys. Lett. 2015, 32 (3): 037302 doi: 10.1088/0256-307X/32/3/037302
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We perform a scanning tunneling microscopy and spectroscopy study on the electronic structures of √3×√3-silicene on Ag(111). It is found that the coupling strength of √3×√3-silicene with the Ag(111) substrate is variable in different regions, giving rise to notable effects in experiments. This evidence of decoupling or variable interaction of silicene with the substrate is helpful to in-depth understanding of the structure and electronic properties of silicene.

A Modified Lattice Model of the Reversible Effect of Axial Strain on the Critical Current of Polycrystalline REBa2Cu3O7−δ Films

GOU Xiao-Fan, ZHU Guang
Chin. Phys. Lett. 2015, 32 (3): 037401 doi: 10.1088/0256-307X/32/3/037401
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The strain effect on the critical current is one of the most important properties for polycrystalline YBa2Cu3O7−δ (REBCO, RE: rare earth) films, in which the reversible effect is intrinsic in the range of strain 0 and the irreversible strain εirr. By introducing the applied strain, a modified lattice model combining the strain and misorientation of grain boundaries (GBs) in the REBCO film is developed. A good agreement of the calculation on the lattice model with the experimental data shows that the lattice model is able to well describe the reversible effect of axial strain on the critical current of the REBCO film, and provides a good understanding of the mechanism of the reversible effect of the strain. Moreover, the effects of the crystallographic texture of the REBCO film and the residual strain εr on the variation of the critical current with the applied strain are extensively investigated. Furthermore, by using the developed lattice model, the irreversible strain εirr of the REBCO film can be theoretically determined by comparing the calculation of the critical current-strain curve with the experimental data.

Fabrication and Characterization of Fe-Doped In2O3 Dilute Magnetic Semiconducting Nanowires

ZHANG Jun-Ran, WU Zhen-Yao, LIU Yu-Jie, LV Zhan-Peng, NIU Wei, WANG Xue-Feng, DU Jun, LIU Wen-Qing, ZHANG Rong, XU Yong-Bing
Chin. Phys. Lett. 2015, 32 (3): 037501 doi: 10.1088/0256-307X/32/3/037501
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Fe-doped In2O3 dilute magnetic semiconducting nanowires are fabricated on Au-deposited Si substrates by the chemical vapor deposition technique. It is confirmed by energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy that Fe has been successfully doped into lattices of In2O3 nanowires. The EDS measurements reveal a large amount of oxygen vacancies existing in the Fe-doped In2O3 nanowires. The Fe dopant exists as a mixture of Fe2+ and Fe3+, as revealed by the XPS. The origin of room-temperature ferromagnetism in Fe-doped In2O3 nanowires is explained by the bound magnetic polaron model.

Magnetostriction Increase of Tb0.3Dy0.7Fe1.95 Alloy Prepared by Solidification in High Magnetic Fields

WANG Kai, LIU Tie, GAO Peng-Fei, WANG Qiang, LIU Yin, HE Ji-Cheng
Chin. Phys. Lett. 2015, 32 (3): 037502 doi: 10.1088/0256-307X/32/3/037502
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Tb0.3Dy0.7Fe1.95 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The results show that with the increase of magnetic flux density, the crystal orientation of the (Tb,Dy)Fe2 phase changed from <113> to <111> direction; the grains in the alloys tended to align along the magnetic field direction; and the magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is remarkably improved. The change in magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is linked to the amount and the crystal orientation behavior of the (Tb,Dy)Fe2 phase.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Impact of Temperature Variation on Performance of Carbon Nanotube Field-Effect Transistor–Based on Chaotic Oscillator: A Quantum Simulation Study

Van Ha Nguyen, Hanjung Song
Chin. Phys. Lett. 2015, 32 (3): 038201 doi: 10.1088/0256-307X/32/3/038201
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We evaluate the impact of temperature on the output behavior of a carbon nanotube field effect transistor (CNFET) based chaotic generator. The sources cause the variations in both current−voltage characteristics of the CNFET device and an overall chaotic circuit is pointed out. To verify the effect of temperature variation on the output dynamics of the chaotic circuit, a simulation is performed by employing the CNFET compact model of Wong et al. in HSPICE with a temperature range from -100°C to 100°C. The obtained results with time series, frequency spectra, and bifurcation diagram from the simulation demonstrate that temperature plays a significant role in the output dynamics of the CNFET-based chaotic circuit. Thus, temperature-related issues should be taken into account while designing a high-quality chaotic generator with high stability.

A High-Efficiency Broadband Superconducting Nanowire Single-Photon Detector with a Composite Optical Structure

GU Min, KANG Lin, ZHANG La-Bao, ZHAO Qing-Yuan, JIA Tao, WAN Chao, XU Rui-Ying, YANG Xiao-Zhong, WU Pei-Heng
Chin. Phys. Lett. 2015, 32 (3): 038501 doi: 10.1088/0256-307X/32/3/038501
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Superconducting nanowire single-photon detectors (SNSPDs) with a composite optical structure composed of phase-grating and optical cavity structures are designed to enhance both the system detection efficiency and the response bandwidth. Numerical simulation by the finite-difference time-domain method shows that the photon absorption capacity of SNSPDs with a composite optical structure can be enhanced significantly by adjusting the parameters of the phase-grating and optical cavity structures at multiple frequency bands. The absorption capacity of the superconducting nanowires reaches 70%, 72%, 60.73%, 61.7%, 41.2%, and 46.5% at wavelengths of 684, 850, 732, 924, 1256, and 1426 nm, respectively. The use of a composite optical structure reduces the total filling factor of superconducting nanowires to only 0.25, decreases the kinetic inductance of SNSPDs, and improves the count rates.

Lateral-Coupled Junctionless IZO-Based Electric-Double-Layer Thin-Film Transistors Gated by Solid-State Phosphosilicate Glass Electrolyte

ZHOU Ju-Mei, GAO Xiao-Hong, ZHANG Hong-Liang
Chin. Phys. Lett. 2015, 32 (3): 038502 doi: 10.1088/0256-307X/32/3/038502
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We describe the lateral-coupled junctionless indium-zinc-oxide (IZO) thin-film transistors (TFTs) in which there are no junctions between channel and source/drain electrodes and with solid-state phosphosilicate glass electrolyte (PSG) gating. Due to the three-dimensional high proton conduction and lateral coupled electric-double-layer (EDL) capacitance (>1 μF/cm2) of the PSG, the low voltage (2.0 V) junctionless IZO TFTs and the dual coplanar gate devices are obtained. An AND logic function is demonstrated on the basis of the junctionless EDL-TFTs. Such devices are promising for applications in pH sensors, humidity sensors, biosensors, and neuron network simulation.
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