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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2015, 32 (11)   Published: 30 October 2015
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The Harmonic Potential Theorem for a Quantum System with Time-Dependent Effective Mass

LAI Meng-Yun, XIAO Duan-Liang, PAN Xiao-Yin
Chin. Phys. Lett. 2015, 32 (11): 110301 doi: 10.1088/0256-307X/32/11/110301
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We investigate the many-body wave function of a quantum system with time-dependent effective mass, confined by a harmonic potential with time-dependent frequency, and perturbed by a time-dependent spatially homogeneous electric field. It is found that the wave function is comprised of a phase factor times the solution to the unperturbed time-dependent Schrödinger equation with the latter being translated by a time-dependent value that satisfies the classical driven equation of motion. The wave function reduces to that of the harmonic potential theorem wave function when both the effective mass and frequency are static. An example of application is also given.

Optimal Size for Maximal Energy Efficiency in Information Processing of Biological Systems Due to Bistability

ZHANG Chi, LIU Li-Wei, WANG Long-Fei, YUE Yuan, YU Lian-Chun
Chin. Phys. Lett. 2015, 32 (11): 110501 doi: 10.1088/0256-307X/32/11/110501
Full Text: [PDF 535 KB] (109)
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Energy efficiency is closely related to the evolution of biological systems and is important to their information processing. In this work, we calculate the excitation probability of a simple model of a bistable biological unit in response to pulsatile inputs, and its spontaneous excitation rate due to noise perturbation. Then we analytically calculate the mutual information, energy cost, and energy efficiency of an array of these bistable units. We find that the optimal number of units could maximize this array's energy efficiency in encoding pulse inputs, which depends on the fixed energy cost. We conclude that demand for energy efficiency in biological systems may strongly influence the size of these systems under the pressure of natural selection.

Target Inactivation and Recovery in Two-Layer Networks

SONG Xin-Fang, WANG Wen-Yuan
Chin. Phys. Lett. 2015, 32 (11): 110502 doi: 10.1088/0256-307X/32/11/110502
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We study the target inactivation and recovery in two-layer networks. Five kinds of strategies are chosen to attack the two-layer networks and to recover the activity of the networks by increasing the inter-layer coupling strength. The results show that we can easily control the dying state effectively by a randomly attacked situation. We then investigate the recovery activity of the networks by increasing the inter-layer coupled strength. The optimal values of the inter-layer coupled strengths are found, which could provide a more effective range to recovery activity of complex networks. As the multilayer systems composed of active and inactive elements raise important and interesting problems, our results on the target inactivation and recovery in two-layer networks would be extended to different studies.

Analytical Results for Frequency-Weighted Kuramoto-Oscillator Networks

LIU Yu-Long, YU Xiao-Ming, HAO Yu-Hua
Chin. Phys. Lett. 2015, 32 (11): 110503 doi: 10.1088/0256-307X/32/11/110503
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The Kuramoto model for an ensemble of coupled oscillators provides a paradigmatic example of non-equilibrium transitions between an incoherent and a synchronized state. A frequency-weighted network of Kuramoto oscillators is proposed, where the oscillators are asymmetrically coupled with the weights depending on their own native frequencies. Moreover, the characteristics of the whole network can be described by a single weighting exponent β. To obtain some analytical results, we focus on three special values of the weighting exponent β. Obviously, the network of oscillators in connection with the heterogeneous coupling scheme turns out to exhibit richer dynamics. Our findings indicate that the weighting exponents should be of importance to affect the network's synchronization ability.

Analysis of the Longitudinal Structure Function FL from the Non-linear Regge Gluon Density Behavior at Low-x

Chin. Phys. Lett. 2015, 32 (11): 111101 doi: 10.1088/0256-307X/32/11/111101
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The longitudinal structure function with shadowing correction according to the nonlinear effects of the gluon density behavior at low x is considered. The solution of the GLR-MQ evolution equation for the gluon density shows that the FLg(x,Q2) behavior can be tamed by the singularity at low x values. Comparing our results with H1 data at R=4 GeV−1 shows that at very low x this behavior is completely tamed by taking shadowing correction into account.

Critical Behavior of Dynamical Chiral Symmetry Breaking with Gauge Boson Mass in QED3

WANG Xiu-Zhen, LI Jian-Feng, YU Xin-Hua, FENG Hong-Tao
Chin. Phys. Lett. 2015, 32 (11): 111102 doi: 10.1088/0256-307X/32/11/111102
Full Text: [PDF 590 KB] (31)
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Since the massless quantum electrodynamics in 2+1 dimensions (QED3) with nonzero gauge boson mass ζ can be used to explain some important traits of high-Tc superconductivity in planar cuprates, it is worthwhile to apply this model to analyze the nature of chiral phase transition at the critical value ζc. Based on the feature of chiral susceptibility, we show that the system at ζc exhibits a second-order phase transition which accords with the nature of appearance of the high-Tc superconductivity, and the estimated critical exponents around ζc are illustrated.

The 't Hooft Coupling and Baryon Mass Splitting in the Large-Nc Quark Model

JIA Duo-Jie, ZHANG Jia-Shen
Chin. Phys. Lett. 2015, 32 (11): 111201 doi: 10.1088/0256-307X/32/11/111201
Full Text: [PDF 602 KB] (29)
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We study the 't Hooft coupling gt and the mass splitting of the ground-state baryons in terms of the large Nc-inspired quark model, by which the Hartree wavefunctions of light quarks are obtained. By fitting the spectra of decuplet and octet baryons, we obtain the 't Hooft coupling gt to be around 1.57. We generalize the scenario to the case of heavy baryons, such as Λc, gt values which does not deviate much from 1.57, as well as to the case of mesons with gt far from that for baryons. The consequence is discussed.

Hyperon Effects on the Spin Parameter of Rotating Neutron Stars

QI Bin, ZHANG Nai-Bo, WANG Shou-Yu, SUN Bao-Yuan
Chin. Phys. Lett. 2015, 32 (11): 112101 doi: 10.1088/0256-307X/32/11/112101
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Based on the equations of state from the relativistic mean field theory without and with the inclusion of strangeness-bearing hyperons, we study the dimensionless spin parameter j=cJ/(GM2) of uniformly rotating neutron stars. It is shown that the maximum value of the spin parameter jmax of a neutron star rotating at the Keplerian frequency fK is jmax∼0.7 when the star mass M >0.5 Mʘ, which is sustained for various versions of equations of state without and with hyperons. The relationship between j and the scaled rotation frequency f/fK is found to be insensitive to the star mass or the adopted equation of state in the models without hyperons. However, the emergence of hyperons in neutron stars will lead to an uncertainty of the spin parameter j, which in turn could generate a complexity in the theoretical study of the quasi-periodic oscillations observed in disk-accreting compact-star systems.

Production and Detection of Ultracold Ground State 85Rb133Cs Molecules in the Lowest Vibrational Level by Short-Range Photoassociation

ZHAO Yan-Ting, YUAN Jin-Peng, LI Zhong-Hao, JI Zhong-Hua, XIAO Lian-Tuan, JIA Suo-Tang
Chin. Phys. Lett. 2015, 32 (11): 113301 doi: 10.1088/0256-307X/32/11/113301
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We investigate the production of ultracold ground state X1Σ+(ν=0) RbCs molecules in the lowest vibrational level via short-range photoassociation followed by spontaneous emission. The starting point is the laser cooled 85Rb and 133Cs atoms in a dual species, forced dark magneto-optical trap. The special intermediate level (5)0+(ν=10) correlated to the (2)3Π electric state is achieved by the photoassociation process. The formed ground state X1Σ+(ν=0) molecule is resonantly excited to the 21Π intermediate state by a 651 nm pulse laser and is ionized by a 532 nm pulse laser and then detected by the time-of-flight mass spectrum. Saturation of the photoionization spectroscopy at large ionization laser energy is observed and the ionization efficiency is obtained from the fitting. The production of ultracold ground state 85Rb133Cs molecules is facilitative for the further research about the manipulation of ultracold molecules in the rovibrational ground state.

Containerless Heating Process of a Deeply Undercooled Metal Droplet by Electrostatic Levitation

WANG Fei-Long, DAI Bin, LIU Xue-Feng, SUN Yi-Ning, SUN Zhi-Bin, YU Qiang, ZHAI Guang-Jie
Chin. Phys. Lett. 2015, 32 (11): 114101 doi: 10.1088/0256-307X/32/11/114101
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We present the containerless heating process of a deeply undercooled metal droplet by electrostatic levitation. The problem of surface charge loss in the heating process is discussed and specific formulas are given to describe the basic process of charge supplement by the photoelectric and thermoelectric effects. The pure metal zirconium is used to be melted and solidified to analyze the heating process. The temperature–time curve clearly shows the features including melting, undercooling, recalescence and solid-state phase transformation.

Localized Effect of Light Diffraction by Capillary Wave

MIAO Yang , NIE Song-Lin
Chin. Phys. Lett. 2015, 32 (11): 114201 doi: 10.1088/0256-307X/32/11/114201
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The localized effect of light diffracted by a capillary wave is discovered by changing the wave amplitude. The localized range is related to the wave number and the amplitude. The dependence of the half maximum localized angle on the wave number and amplitude is analytically derived. Meanwhile, the analytic angular distribution of the diffraction light in the localized range is obtained. Experiments are carried out to achieve diffraction patterns to confirm the localized effect and to measure the angular distribution of the diffraction light intensity as well as to determine the localized range scales corresponding to different wave amplitudes. Theoretical curves of the light intensity angular distribution and localized interval widths related to surface acoustic wave amplitudes are compared with the experimental data. The experimental results agree well with the theoretical prediction.

High-Pulse-Energy All-Normal-Dispersion Yb-Doped Fiber Laser Based on Nonlinear Polarization Evolution

WANG Jun-Li, WANG Xue-Ling, HE Bo-Rong, WANG Yong-Gang, ZHU Jiang-Feng, WEI Zhi-Yi
Chin. Phys. Lett. 2015, 32 (11): 114202 doi: 10.1088/0256-307X/32/11/114202
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We report an all-normal-dispersion ytterbium fiber laser mode locked by nonlinear polarization evolution. With a 347-m-long all-fiber ring cavity, a pulse energy of 263 nJ at a repetition rate of 613 kHz is achieved, which is the highest per-pulse energy directly obtained from an all-fiber mode-locked laser doped by ytterbium ions. The compact and operation-robust laser yields a well-shaped spectrum centered at 1032 nm with a bandwidth (FWHM) of 4 nm, and the slope efficiency is as high as 27.5%. The proposed low-repetition-rate high-pulse-energy mode-locked fiber laser will be a promising seed for all-fiber chirped pulsed amplification systems.

Effects of Finite Surface on Polarization State of Thermal Emission

LIU Fei, SHAO Xiao-Peng, XIANGLI Bin, GAO Ying, HAN Ping-Li, WANG Lin
Chin. Phys. Lett. 2015, 32 (11): 114203 doi: 10.1088/0256-307X/32/11/114203
Full Text: [PDF 2639 KB] (25)
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A comprehensive model for explaining the polarization properties of thermal emission is presented for the case of objects with certain sizes. Using Stokes theory and the superposition principle of a light wave, we analyze the dependence of degree of linear polarization on the spatial geometrical relations including the sizes of objects, the detection distance, and the locations of objects for both metallic and nonmetallic objects, each taken separately.

Experimental Investigation of All-Optical NRZ-DPSK to RZ-DPSK Format Conversion Based on TOAD

MAO Ya-Ya, SHENG Xin-Zhi, WU Chong-Qing, ZHANG Tian-Yong, WANG Ying
Chin. Phys. Lett. 2015, 32 (11): 114204 doi: 10.1088/0256-307X/32/11/114204
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We propose and experimentally demonstrate a novel all-optical non-return-to-zero differential-phase-shift-keying (NRZ-DPSK) to return-to-zero differential-phase-shift-keying (RZ-DPSK) format conversion scheme. This scheme is based on the terahertz optical asymmetric demultiplexer (TOAD). A 10 Gb/s converted RZ-DPSK signal is obtained with a wide duty cycle tuning range from 16% to 66%. For all converted RZ-DPSK signals, the receiver sensitivities at BER of 10−9 are 0.4 to 1.7 dB higher compared with the original NRZ-DPSK signal. The clear and open eye diagrams are presented to demonstrate the high quality format conversion performance. Moreover, the optical spectra show that this conversion is in a wavelength-preserving operation.

A Narrow Linewidth Continuous Wave Ho:YAG Laser Pumped by a Tm:YLF Laser

BAI Fang, CHEN Xin-Yu, LIU Jing-Liang, WU Chun-Ting, HUANG Zhu-Long, JIN Guang-Yong
Chin. Phys. Lett. 2015, 32 (11): 114205 doi: 10.1088/0256-307X/32/11/114205
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A narrow linewidth cw Ho:YAG laser pumped by a 1908 nm Tm:YLF laser based on the volume Bragg grating is established. The maximum output power of 9.6 W for the incident pump power of 16.9 W is obtained, and the corresponding slope efficiency and optical-to-optical conversion efficiency are 67.2% and 56.8%, respectively. The Ho:YAG laser operates stably at 2122.1 nm by using two Fabry–Perot etalons, with a full width at half maximum less than 0.2 nm.

An Effective Thermal Splicing Method to Join Fluoride and Silica Fibers for a High Power Regime

ZHENG Zhi-Jian, OUYANG De-Qin, ZHAO Jun-Qing, RUAN Shuang-Chen, YU Jun, GUO Chun-Yu, WANG Jin-Zhang
Chin. Phys. Lett. 2015, 32 (11): 114206 doi: 10.1088/0256-307X/32/11/114206
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A repeatable and simple thermal splicing method for low loss splice between fluoride and silica fibers is presented. The minimum splicing loss of 0.58 dB is achieved experimentally with this approach. Meanwhile, the power capacity of this splicing joint is also tested with a high power fiber laser. The maximum input power is up to 15 W, only limited by the available power of the laser source. To the best of our knowledge, this is the first report on thermal splicing between fluoride and silica fibers operating in a high power regime without any complicated ion-assisted deposition process.

H2 Stimulated Raman Scattering in a Multi-pass Cell with a Herriott Configuration

CAI Xiang-Long, ZHOU Can-Hua, ZHOU Dong-Jian, LIU Jin-Bo, GUO Jing-Wei, GUI Lin
Chin. Phys. Lett. 2015, 32 (11): 114207 doi: 10.1088/0256-307X/32/11/114207
Full Text: [PDF 669 KB] (26)
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Stimulated raman scattering (SRS) is an effective method for expanding the spectral range of high power lasers, especially in the regime of near IR and middle IR. We report the SRS of high pressure H2 with a multiple-pass cell configuration. The SRS with the multiple-pass cell configuration is found to be very efficient for reduction of threshold of the first Stokes (S1). Due to the coherent SRS (CSRS) process, the multiple-pass cell configuration is more effective for reduction of the threshold for the second Stokes (S2) SRS and for increasing the conversion efficiency of S2. This contributes to the relatively low conversion efficiency of S1 for the multiple-pass cell configuration. Multiple-pass cell SRS is also found to be very effective for improving the beam quality and the stability of S1.

Color Ghost Imaging with Pseudo-White-Thermal Light

CAO De-Zhong, XU Bao-Long, ZHANG Su-Heng, WANG Kai-Ge
Chin. Phys. Lett. 2015, 32 (11): 114208 doi: 10.1088/0256-307X/32/11/114208
Full Text: [PDF 703 KB] (68)
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A pseudo-white-thermal light source is prepared by projecting three (red, green, and blue) laser beams onto a rotating ground glass disk. Based on the RGB color model, we investigate the color Hanbury-Brown-Twiss (HBT) effect and color ghost imaging with thermal light. The color HBT effect indicates that photons of the same color will bunch. This fact ensures the chromatic discrimination power of ghost imaging with thermal light. We retrieve the RGB ingredients of the object through intensity correlation measurements. A method of white balance to properly form the ghost images is proposed.

Hydrodynamic Sensing Based on Surface-Modified Flexible Nanocomposite Film

SHU Yi, TIAN He, WANG Zhe, ZHAO Hai-Ming, MI Wen-Tian, LI Yu-Xing, CAO Hui-Wen, REN Tian-Ling
Chin. Phys. Lett. 2015, 32 (11): 114301 doi: 10.1088/0256-307X/32/11/114301
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A highly sensitive sensor with piezoresistive nanocomposite material assembled in a flexible composite film is designed and tested for hydrodynamic sensing. Within the device, two nanocomposite films with micrometer scale modified small bumps on the surface are arranged together face-to-face by the interlocking mechanism. These structures are verified to have full-scale piezoresistive high sensitivities which are very appropriate for underwater sensing. Obvious output signals can be observed from the device subjected to the hydroacoustic dipole (vibrating sphere) with exciting frequency from 10 Hz to 40 Hz. A spectral peak can be seen in the Fourier analysis of the output signal at the corresponding frequency.

Excitation of Zonal Flows by ion-temperature-gradient Modes Excited by the Fluid Resonance

Chin. Phys. Lett. 2015, 32 (11): 115201 doi: 10.1088/0256-307X/32/11/115201
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We apply the reductive perturbation method to the simple electrostatic ion-temperature-gradient mode in an advanced fluid description. The fluid resonance turns out to play a major role for the excitation of zonal flows. This is the mechanism recently found to lead to the low-to-high (L–H) mode transition and to the nonlinear Dimits upshift in transport code simulations. It is important that we have taken the nonlinear temperature dynamics from the Reynolds stress as the convected diamagnetic flow. This has turned out to be the most relevant effect as found in transport simulations of the L–H transition, internal transport barriers and Dimits shift. This is the first time that an analytical method is applied to a system which numerically has been found to give the right experimental dynamics.

Parametric Instabilities of Parallel Propagating Circularly Polarized Alfvén Waves: One-Dimensional Hybrid Simulations

HE Peng, GAO Xin-Liang, LU Quan-Ming, ZHAO Jin-Song
Chin. Phys. Lett. 2015, 32 (11): 115202 doi: 10.1088/0256-307X/32/11/115202
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By performing one-dimensional (1-D) hybrid simulations, we analyze in detail the parametric instabilities of the Alfvén waves with a spectrum in a low beta plasma. The parametric instabilities experience two stages. In the first stage, the density modes are excited and immediately couple with the pump Alfvén waves. In the second stage, each pump Alfvén wave decays into a density mode and a daughter Alfvén mode similar to the monochromatic cases. Furthermore, the proton velocity beam will also be formed after the saturation of the parametric instabilities. When the plasma beta is high, the parametric decay in the second stage will be strongly suppressed.

Local Five-Fold Symmetry and Diffusion Behavior of Zr64Cu36 Amorphous Alloy Based on Molecular Dynamics

GAO Wei, FENG Shi-Dong, QI Li, ZHANG Shi-Liang, LIU Ri-Ping
Chin. Phys. Lett. 2015, 32 (11): 116101 doi: 10.1088/0256-307X/32/11/116101
Full Text: [PDF 604 KB] (31)
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A molecular dynamics simulation is performed to investigate the relationship between the local five-fold symmetry and the diffusion behavior involved in the rapid solidification of a Zr64Cu36 alloy melt. The Voronoi polyhedron analysis indicates that the icosahedral clusters cannot explain the total amorphous structure, while the local five-fold symmetry shows more advantage in describing the relationship between the transition of the clusters and the diffusion behavior of Zr64Cu36 amorphous alloy. It is found that when the fraction of the local five-fold symmetry is less than 0.3, the diffusion coefficient increases significantly, and when the value exceeds 0.7, diffusion behavior is inhibited. The simulation provides a new viewpoint for understanding of the glass-forming mechanism.

Illumination and Voltage Dependence of Electrical Characteristics of Au/0.03 Graphene-Doped PVA/n-Si Structures via Capacitance/Conductance–Voltage Measurements

SAHAR Alialy, AHMET Kaya, İ Uslu, ŞEMSETTIN Altındal
Chin. Phys. Lett. 2015, 32 (11): 116102 doi: 10.1088/0256-307X/32/11/116102
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Au/n-Si (MS) structures with a high dielectric interlayer (0.03 graphene-doped PVA) are fabricated to investigate the illumination and voltage effects on electrical and dielectric properties by using capacitance–voltage (CV) and conductance–voltage (G/ωV) measurements at room temperature and at 1 MHz. Some of the main electrical parameters such as concentration of doping atoms (ND), barrier height (ϕB(C−V)), depletion layer width (WD) and series resistance (Rs) show fairly large illumination dispersion. The voltage-dependent profile of surface states (Nss) and resistance of the structure (Ri) are also obtained by using the dark-illumination capacitance (CdarkCill) and Nicollian–Brews methods, respectively. For a clear observation of changes in electrical parameters with illumination, the values of ND, WD, ϕB(C−V) and Rs are drawn as a function of illumination intensity. The values of ND and WD change almost linearly with illumination intensity. On the other hand, Rs decreases almost exponentially with increasing illumination intensity whereas ϕB(C−V) increases. The experimental results suggest that the use of a high dielectric interlayer (0.03 graphene-doped PVA) considerably passivates or reduces the magnitude of the surface states. The large change or dispersion in main electrical parameters can be attributed to generation of electron-hole pairs in the junction under illumination and to a good light absorption. All of these experimental results confirm that the fabricated Au/0.03 graphene-doped PVA/n-Si structure can be used as a photodiode or a capacitor in optoelectronic applications.

Forces Acting on Submillimeter Spheres at the Air–Water Interface

WANG Le-Feng, LIU Lu, XU Hui-Chao, RONG Wei-Bin, SUN Li-Ning
Chin. Phys. Lett. 2015, 32 (11): 116801 doi: 10.1088/0256-307X/32/11/116801
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The forces acting on submillimeter spheres at the air–water interface are investigated theoretically and experimentally. To calculate the capillary force acting on the sphere, an iterative method is used to determine the immersing position of the liquid interface on the sphere for a given distance. Then the total forces acting on the sphere are considered. The scaling effects of the net force acting on the sphere at the air–water interface are demonstrated. For the experiments, the force-position relationship of microspheres is measured with a precise electronic balance. The results show that the evaporation of the liquid in the container affects the measuring results greatly under ambient conditions. After considering the evaporation compensation, there is a great agreement between the theoretical and experimental results. Obvious hysteresis phenomena of the force-distance curve during the emersion processes are also observed and explained.

Improvement of Surface Morphology of Yttrium-Stabilized Zirconia Films Deposited by Pulsed Laser Deposition on Rolling Assisted Biaxially Textured Substrate Tapes

WANG Meng-Lin, LIU Lin-Fei, LI Yi-Jie,
Chin. Phys. Lett. 2015, 32 (11): 116802 doi: 10.1088/0256-307X/32/11/116802
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The surface morphology of buffer layer yttrium-stabilized zirconia (YSZ) of YBa2Cu3O7−σ (YBCO) high temperature superconducting films relies on a series of controllable experimental parameters. In this work, we focus on the influence of pulsed laser frequency and target crystalline type on surface morphology of YSZ films deposited by pulsed laser deposition (PLD) on rolling assisted biaxially textured substrate tapes. Usually two kinds of particles are observed in the YSZ layer: randomly distributed ones on the whole film and self-assembled ones along grain boundaries. SEM images are used to prove that particles can be partly removed when choosing dense targets of single crystalline. Lower frequency of pulsed laser also contributes to a smoother film surface. TEM images are used to view the crystalline structure of thin film. Thus we can obtain a basic understanding of how to prepare a particle-free YSZ buffer layer for YBCO in optimized conditions using PLD. The YBCO layer with nice structure and critical current density of around 5 MA/cm2 can be reached on smooth YSZ samples.

Phonon-Assisted Spin Current in Single Molecular Magnet Junctions

NIU Peng-Bin, SHI Yun-Long, SUN Zhu, NIE Yi-Hang, LUO Hong-Gang
Chin. Phys. Lett. 2015, 32 (11): 117201 doi: 10.1088/0256-307X/32/11/117201
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Owing to the bistable character of the single molecular magnet (SMM), it can generate 100% spin-polarized currents even connected with normal (N) leads. In this work, we study the phonon-assisted spin current in N-SMM-N systems. We mainly focus on the interplay of SMM's bistable character and electron–phonon coupling. It is found that when SMM is trapped in one of the lowest bistable states, it can generate phonon-assisted spin-polarized currents. At the up-spin transport channel, it is accompanied by a phonon-assisted up-spin current, while at the down-spin transport channel, it is accompanied by a phonon-assisted down-spin current.

Al0.30Ga0.70N/GaN/Al0.07Ga0.93N Double Heterostructure High Electron Mobility Transistors with a Record Saturation Drain Current of 1050 mA/mm

LI Xiang-Dong, ZHANG Jin-Cheng, GUO Zhen-Xing, JIANG Hai-Qing, ZOU Yu, ZHANG Wei-Hang, HE Yun-Long, JIANG Ren-Yuan, ZHAO Sheng-Lei, HAO Yue
Chin. Phys. Lett. 2015, 32 (11): 117202 doi: 10.1088/0256-307X/32/11/117202
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We report Al0.30Ga0.70N/GaN/Al0.07Ga0.93N double heterostructure high electron mobility transistors with a record saturation drain current of 1050 mA/mm. By optimizing the graded buffer layer and the GaN channel thickness, both the crystal quality and the device performance are improved significantly, including electron mobility promoted from 1535 to 1602 cm2/V⋅s, sheet carrier density improved from 0.87×1013 to 1.15×1013 cm−2, edge dislocation density reduced from 2.4×109 to 1.3×109 cm−2, saturation drain current promoted from 757 to record 1050 mA/mm, mesa leakage reduced by two orders in magnitude, and breakdown voltage promoted from 72 to 108 V.

Express Methods for Measurement of Electroconductivity of Semiconductor Layered Crystal

Chin. Phys. Lett. 2015, 32 (11): 117203 doi: 10.1088/0256-307X/32/11/117203
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We describe theoretically the grounded method of measuring the conductivity of anisotropic layered semiconductor materials. The suggested method implies the use of a four-probe testing device with a linear arrangement of probes. The final expressions for identifying the electrical conductivity are presented in the form of a series of analytic functions. The suggested method is experimentally verified, and practical recommendations of how to apply it are also provided.

Improvement of Metal-Graphene Ohmic Contact Resistance in Bilayer Epitaxial Graphene Devices

HE Ze-Zhao, YANG Ke-Wu, YU Cui, LI Jia, LIU Qing-Bin, LU Wei-Li, FENG Zhi-Hong, CAI Shu-Jun
Chin. Phys. Lett. 2015, 32 (11): 117204 doi: 10.1088/0256-307X/32/11/117204
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We report on an improved metal-graphene ohmic contact in bilayer epitaxial graphene on a SiC substrate with contact resistance below 0.1 Ω⋅mm. Monolayer and bilayer epitaxial graphenes are prepared on a 4H-SiC substrate in this work. Their contact resistances are measured by a transfer length method. An improved photoresist-free device fabrication method is used and is compared with the conventional device fabrication method. Compared with the monolayer graphene, the contact resistance Rc of bilayer graphene improves from an average of 0.24 Ω⋅mm to 0.1 Ω⋅mm. Ohmic contact formation mechanism analysis by Landauer's approach reveals that the obtained low ohmic contact resistance in bilayer epitaxial graphene is due to their high carrier density, high carrier transmission probability, and p-type doping introduced by contact metal Au.

Room-Temperature Organic Negative Differential Resistance Device Using CdSe Quantum Dots as the ITO Modification Layer

JIAO Bo, YAO Li-Juan, WU Chun-Fang, DONG Hua, HOU Xun, WU Zhao-Xin
Chin. Phys. Lett. 2015, 32 (11): 117301 doi: 10.1088/0256-307X/32/11/117301
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Room-temperature negative differential resistance (NDR) has been observed in different types of organic materials. However, detailed study on the influence of the organic material on NDR performance is still scarce. In this work, room-temperature NDR is observed when CdSe quantum dot (QD) modified ITO is used as the electrode. Furthermore, material dependence of the NDR performance is observed by selecting materials with different charge transporting properties as the active layer, respectively. A peak-to-valley current ratio up to 9 is observed. It is demonstrated that the injection barrier between ITO and the organic active layer plays a decisive role for the device NDR performance. The influence of the aggregation state of CdSe QDs on the NDR performance is also studied, which indicates that the NDR is caused by the resonant tunneling process in the ITO/CdSe QD/organic active layer structure.

Positive Bias Temperature Instability and Hot Carrier Injection of Back Gate Ultra-thin-body In0.53Ga0.47As-on-Insulator n-Channel Metal-Oxide-Semiconductor Field-Effect Transistor

TANG Xiao-Yu, LU Ji-Wu, ZHANG Rui, WU Wang-Ran, LIU Chang, SHI Yi, HUANG Zi-Qian, KONG Yue-Chan, ZHAO Yi
Chin. Phys. Lett. 2015, 32 (11): 117302 doi: 10.1088/0256-307X/32/11/117302
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Ultra-thin-body (UTB) In0.53Ga0.47As-on-insulator (In0.53Ga0.47As-OI) structures with thicknesses of 8 and 15 nm are realized by transferring epitaxially grown In0.53Ga0.47As layers to silicon substrates with 15-nm-thick Al2O3 as a buried oxide by using the direct wafer bonding method. Back gate n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs) are fabricated by using these In0.53Ga0.47As-OI structures with excellent electrical characteristics. Positive bias temperature instability (PBTI) and hot carrier injection (HCI) characterizations are performed for the In0.53Ga0.47As-OI nMOSFETs. It is confirmed that the In0.53Ga0.47As-OI nMOSFETs with a thinner body thickness suffer from more severe degradations under both PBTI and HCI stresses. Moreover, the different evolutions of the threshold voltage and the saturation current of the UTB In0.53Ga0.47As-OI nMOSFETs may be due to the slow border traps.

Nanojunctions Contributing to High Performance Thermoelectric ZnO-Based Inorganic–Organic Hybrids

WU Zi-Hua, XIE Hua-Qing, WANG Yuan-Yuan, XING Jiao-Jiao, MAO Jian-Hui
Chin. Phys. Lett. 2015, 32 (11): 117303 doi: 10.1088/0256-307X/32/11/117303
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Organic–inorganic nanojunctions can result in a selective scattering of charge carrier depending on their energy, which leads to a simultaneous increase in the Seebeck coefficient S and the power factor. In this work, the nanojunction is successfully employed at the organic–inorganic semiconductor interface of polyparaphenylene (PPP) and Zn1−xAgxO nanoparticles through the sol-gel method. The presence of nanoinclusions PPP in Zn0.9Ag0.1O matrix is found to be effective in improving the figure of merit (ZT) by the dual effects of an increase in the power factor consistent with the heterojunction effect and a reduction in thermal conductivity. Zn0.9Ag0.1O/0.1 wt% PPP exhibits a maximum figure of merit, i.e., ZT = 0.22.

Miniband Formation in GaN/AlN Constant-Total-Effective-Radius Multi-shell Quantum Dots

Solaimani M.
Chin. Phys. Lett. 2015, 32 (11): 117304 doi: 10.1088/0256-307X/32/11/117304
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We study the procedure of miniband formation in GaN/AlN constant-total-effective-radius multi-shell quantum dots (CTER-MSQDs) by calculating the subband energies. We find a different behavior of the miniband widths and miniband gaps when the number of wells changes. It is shown that with increasing the inner quantum dot radius Rin, the number of minigaps decreases; with increasing the outer quantum dot radius Rout, the number of minigaps increases. We show that in the CTER-MSQDs systems, two kinds of minigaps exist: in the type (i) ones, minigaps increase monotonically when the number of wells increases while in the type (ii) ones, with increasing the number of wells, some of minigaps create, increase, at a critical number of wells decrease and finally vanish. Thus tuning of the minigaps and miniband widths in the CTER-MSQDs systems by using the number of wells, inner and outer quantum dot radii Rin and Rout is now possible.

Superconductivity in Pd-Intercalated Ternary Rare-Earth Polychalcogenide NdSeTe2

WANG Pei-Pei, XUE Mian-Qi, LONG Yu-Jia, ZHAO Ling-Xiao, CAI Yao, YANG Huai-Xin, LI Jian-Qi, REN Zhi-An, CHEN Gen-Fu
Chin. Phys. Lett. 2015, 32 (11): 117401 doi: 10.1088/0256-307X/32/11/117401
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We synthesize a set of Pd-doped polycrystalline samples PdxNdSeTe2 and measure their physical properties. Compared with pure NdSeTe2, the charge density wave (CDW) order is continuously suppressed with the Pd-intercalation. Bulk superconductivity first appears at x=0.06 with Tc nearly 2.5 K, coexisting with a CDW transition at 176 K. Further Pd-doping enhances Tc, until it reaches the maximum value 2.84 K at x=0.1, meanwhile the CDW transition vanishes. The upper critical field for the optimal doping sample Pd0.1NdSeTe2 is determined from the R–H measurement, which is estimated to be 0.6 T. These results provide another kind of ideal compound for studying the interplay between CDW and superconductivity systematically.

Electronic Structure Properties in the Nematic Phases of FeSe

LIANG Yi, WU Xian-Xin, HU Jiang-Ping
Chin. Phys. Lett. 2015, 32 (11): 117402 doi: 10.1088/0256-307X/32/11/117402
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We investigate the electronic structures of FeSe in the presence of different possible orders and spin-orbit coupling (SOC). It is found that only the ferro-orbital order (FO) and the collinear antiferro-magnetism (C-AFM) can simultaneously induce splittings at Γ and M. Bicollinear antiferro-magnetism (B-AFM) and SOC have very similar band structures on ΓM near the Fermi level. The temperature T insensitive splitting at Γ and the T-dependent splitting at M observed in recent experiments can be explained by the d-wave bond nematic (dBN) order together with SOC. The recent observed Dirac cones and their T-dependence in FeSe thin films can also be well explained by the dBN order together with the band renormalization. Their thickness- and cobalt-doping-dependent behaviors are the consequences of electron doping and reduction of Se height. All these suggest that the nematic order in the FeSe system is the dBN order.

Electric-Field Tunability of Dielectric in Polycrystalline Sr1−xMnxTiO3 Thin Films

HOU Yan-Yan, HE Ju, XU Ting-Ting, XIAO Shu-Yu, LU Xue-Liang , HUANG Feng-Zhen, LU Xiao-Mei, ZHU Jin-Song
Chin. Phys. Lett. 2015, 32 (11): 117701 doi: 10.1088/0256-307X/32/11/117701
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The electric-field tunability of dielectric constant (ϵE) in Sr1−xMnxTiO3 films (x=0, 0.005, 0.010, 0.020 and 0.030) prepared by the metal organic decomposition method on Pt/Ti/SiO2/Si substrates is studied in the frequency range from 100 Hz to 1 MHz with different Mn contents at different temperatures. The frequency-independent tunability increases strongly with decreasing the temperature from 300 K to 150 K. The tunability (∼31%) in thin films (x=0.005) at 150 K is obtained and the temperature for the same tunability in ceramics is about 60 K lower than the present one. This tunability is comparable with that in one of ferroelectric Sr1−1.5xBixTiO3 thin films. Similarly, the well-defined P(E) hysteresis loop and 2Pr (1.2 μC/cm2) can be obtained at 300 K in Sr1−xMnxTiO3 films with x=0.005. Both the existence of electric dipole or poled micro domain introduced by the doped Mn2+ located in the off-center position at Sr sites and the strain between the thin film and the substrate are the origins of the tunable and polar behavior in Sr1−xMnxTiO3 films.

Tuning Photoluminescence Performance of Monolayer MoS2 via H2O2 Aqueous Solution

CHENG Ying, WANG Jun-Zhuan, WEI Xiao-Xu, GUO Dan, WU Bing, YU Lin-Wei, WANG Xin-Ran, SHI Yi
Chin. Phys. Lett. 2015, 32 (11): 117801 doi: 10.1088/0256-307X/32/11/117801
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We demonstrate a simple while very effective approach to tune the photoluminescence (PL) performance of monolayer MoS2 by dipping into the H2O2 aqueous solution, which is a strong oxidizer that extracts electrons from the MoS2 sheet within several seconds without damaging the crystal structure. During this process, the trion (electron-coupled exciton, X) is transformed into an exciton (Xo), and thus achieves a greatly enhanced PL performance. These results indicate a convenient way to tune and to control the PL luminescence from monolayer MoS2 and thus lay a basis for the MoS2-based optoelectronic application.

The Evolution of the Extinction and Growth Mechanism of the Silver Nanoplates

PENG Xiao-Niu, WANG Ya-Lan, WANG Hao
Chin. Phys. Lett. 2015, 32 (11): 117802 doi: 10.1088/0256-307X/32/11/117802
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The time-dependence evolution of the extinction spectra of the silver nanoplates is studied to analyze the underlying physical mechanism of the growth process. As the synthesis cycles increase, the wavelength of the absorption peak is first blue-shifted and then is followed by the red shift, attributing to the mode alteration of the longitudinal surface plasmon resonance of the silver nanoplates. The capping agents are also optimized for the convenient and speedy growth of the large integrated Ag nanostructure. These observations expand the comprehensive understanding of plasmon resonance of the Ag nanoplates, and give a better manipulation of their applications in the plasmonic nanodevices.

Conversion Efficiency Enhancement of Multi-crystalline Si Solar Cells by Using a Micro-structured Junction

LI Li, YU Dong, WU Shi-Liang, WANG Wei, LIU Wen-Chao, WU Xiao-Shan, ZHANG Feng-Ming
Chin. Phys. Lett. 2015, 32 (11): 118401 doi: 10.1088/0256-307X/32/11/118401
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A new approach for enhancing the conversion efficiency of solar cells is proposed. A surface with columnar structures is employed on the fabrication of multi-crystalline silicon solar cells, for increasing the collection probability of photon-generated minority carriers in the cells. For comparison, three types of surfaces (planar surface, surfaces with columns of 12 μm in radius and columns of 9 μm in radius, respectively) are used. It is demonstrated that the cells with columnar structured surfaces have better spectral response and higher efficiencies than the cells with planar surface, while the cells with columns of 9 μm in radius show better spectral response than the cells with columns of 12 μm in radius. However, the cells with columns of 12 μm exhibit higher efficiencies than the cells with columns of 9 μm in radius for their difference in fill factors. Moreover, the effect of the columnar structured surface on the minority carrier collection efficiency is verified with wafers of different minority carrier lifetimes (0.5 μs and 1.0 μs). This work may significantly consider its potential in the manufacturing of high-efficiency solar cells at low cost by using low quality materials.

High-Frequency AlGaN/GaN High-Electron-Mobility Transistors with Regrown Ohmic Contacts by Metal-Organic Chemical Vapor Deposition

GUO Hong-Yu, LV Yuan-Jie, GU Guo-Dong, DUN Shao-Bo, FANG Yu-Long, ZHANG Zhi-Rong, TAN Xin, SONG Xu-Bo, ZHOU Xing-Ye, FENG Zhi-Hong
Chin. Phys. Lett. 2015, 32 (11): 118501 doi: 10.1088/0256-307X/32/11/118501
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Nonalloyed ohmic contacts regrown by metal-organic chemical vapor deposition are performed on AlGaN/GaN high-electron-mobility transistors. Low ohmic contact resistance of 0.15 Ω⋅mm is obtained. It is found that the sidewall obliquity near the regrown interface induced by the plasma dry etching has great influence on the total contact resistance. The fabricated device with a 100-nm T-shaped gate demonstrates a maximum drain current density of 0.95 A/mm at Vgs=1 V and a maximum peak extrinsic transcondutance Gm of 216 mS/mm. Moreover, a current gain cut-off frequency fT of 115 GHz and a maximum oscillation frequency fmax of 127 GHz are achieved.

All-Atom Direct Folding Simulation for Proteins Using the Accelerated Molecular Dynamics in Implicit Solvent Model

LI Zong-Chao, DUAN Li-Li, FENG Guo-Qiang, ZHANG Qing-Gang
Chin. Phys. Lett. 2015, 32 (11): 118701 doi: 10.1088/0256-307X/32/11/118701
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We report the results of protein folding (2I9M, C34, N36, 2KES, 2KHK) by the method of accelerated molecular dynamics (aMD) at room temperature with the implicit solvent model. Starting from the linear structures, these proteins successfully fold to the native structure in a 100-ns aMD simulation. In contrast, they are failed under the traditional MD simulation in the same simulation time. Then we find that the lowest root mean square deviations of helix structures from the native structures are 0.36 Å, 0.63 Å, 0.52 Å, 1.1 Å and 0.78 Å. What is more, native contacts, cluster and free energy analyses show that the results of the aMD method are in accordance with the experiment very well. All analyses show that the aMD can accelerate the simulation process, thus we may apply it to the field of computer aided drug designs.

Co-operation and Phase Behavior under the Mixed Updating Rules

ZHANG Wen, LI Yao-Sheng, XU Chen
Chin. Phys. Lett. 2015, 32 (11): 118901 doi: 10.1088/0256-307X/32/11/118901
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We present a model by considering two updating rules when the agents play prisoner's dilemma on a square lattice. Agents can update their strategies by referencing one of his neighbors of higher payoffs under the imitation updating rule or directly replaced by one of his neighbors according to the death-birth updating rule. The frequency of co-operation is related to the probability q of occurrence of the imitation updating or the death-birth updating and the game parameter b. The death-birth updating rule favors the co-operation while the imitation updating rule favors the defection on the lattice, although both rules suppress the co-operation in the well-mixed population. Therefore a totally co-operative state may emerge when the death-birth updating is involved in the evolution when b is relatively small. We also obtain a phase diagram on the qb plane. There are three phases on the plane with two pure phases of a totally co-operative state and a totally defective state and a mixing phase of mixed strategies. Based on the pair approximation, we theoretically analyze the phase behavior and obtain a quantitative agreement with the simulation results.

Phase Transitions of Majority-Vote Model on Modular Networks

HUANG Feng, CHEN Han-Shuang, SHEN Chuan-Sheng
Chin. Phys. Lett. 2015, 32 (11): 118902 doi: 10.1088/0256-307X/32/11/118902
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We investigate the phase transitions behavior of the majority-vote model with noise on a topology that consists of two coupled random networks. A parameter p is used to measure the degree of modularity, defined as the ratio of intermodular to intramodular connectivity. For the networks of strong modularity (small p), as the level of noise f increases, the system undergoes successively two transitions at two distinct critical noises, fc1 and fc2. The first transition is a discontinuous jump from a coexistence state of parallel and antiparallel order to a state that only parallel order survives, and the second one is continuous that separates the ordered state from a disordered state. As the network modularity worsens, fc1 becomes smaller and fc2 does not change, such that the antiparallel ordered state will vanish if p is larger than a critical value of pc. We propose a mean-field theory to explain the simulation results.
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