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Volume 31 Issue 1
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GENERAL
Darboux Transformations via Lie Point Symmetries: KdV Equation
LI Yu-Qi, CHEN Jun-Chao, CHEN Yong, LOU Sen-Yue
Chin. Phys. Lett. 2014, 31 (1): 010201 .   DOI: 10.1088/0256-307X/31/1/010201
Abstract   PDF(pc) (428KB) ( 587 )
By localizing the nonlocal symmetries of a nonlinear model to local symmetries of an enlarged system, we find Darboux-B?cklund transformations for both the original and prolonged systems. The idea is explicitly realized for the well-known KdV equation.
Joint Remote State Preparation of a Four-Dimensional Quantum State
PENG Jia-Yin, BAI Ming-Qiang, MO Zhi-Wen
Chin. Phys. Lett. 2014, 31 (1): 010301 .   DOI: 10.1088/0256-307X/31/1/010301
Abstract   PDF(pc) (483KB) ( 366 )

We present several protocols for joint remote state preparation of a single(two)-quadbit state with real (or complex) coefficients via a projective or positive operator-valued measure. In our schemes, three(five)-quadbit non-maximally entangled state(s) have been employed as the quantum channel and several appropriate mutually orthogonal basis are delicately constructed. Finally, the present schemes are extended to the (N+M) senders' case.

Stabilizing Geometric Phase by Detuning in a Non-Markovian Dissipative Environment
XIAO Xing, LI Yan-Ling
Chin. Phys. Lett. 2014, 31 (1): 010302 .   DOI: 10.1088/0256-307X/31/1/010302
Abstract   PDF(pc) (502KB) ( 386 )
The geometric phase of a two-level atom non-resonantly coupled to a non-Markovian dissipative environment is investigated. Compared to an earlier work [Chen J. J. et al. Phys. Rev. A 81 (2010) 022120] in which the non-Markovian effect has a serious correction on geometric phase, we find that the geometric phase can be stabilized by detuning in non-Markovian dissipative decoherence. Moreover, the geometric phase approaches the unitary geometric phase with the increase of detuning for any initial polar angle, which shows that the geometric phase is not only resilient to the Markovian noise but is also resilient to the non-Markovian noise when a large detuning between the qubit and environment is considered. Our results may be helpful for geometric quantum computation.
Coherent Destruction of Tunneling of Dipolar Bosonic Gas
YU Zi-Fa, ZHANG Ai-Xia, XUE Ju-Kui
Chin. Phys. Lett. 2014, 31 (1): 010303 .   DOI: 10.1088/0256-307X/31/1/010303
Abstract   PDF(pc) (775KB) ( 252 )
The tunneling dynamics of a dipolar bosonic gas with repulsive interactions in a periodically driven triple-well are investigated. Because of the coupled effect of long-range dipole-dipole interaction and the short-range of on-site interaction, the increase of the repulsive atomic interactions can either suppress tunneling or enhance tunneling and, thus, the system experiences rich coherent tunneling(CT)-coherent destruction of tunneling (CDT) transitions. In particular, as the repulsive atomic interactions increase, the system can undergo CT-CDT-CT-CDT or CDT-CT-CDT-CT-CDT transitions. This cannot occur in non-dipolar gas, where the increase of the repulsive atomic interaction only suppress tunneling and the system can only undergo CT-CDT transition. We further present a good understanding of the results with the help of the quasi-energy spectrum of the system.
Oscillating Quintom Model with Time Periodic Varying Deceleration Parameter
SHEN Ming, ZHAO Liang
Chin. Phys. Lett. 2014, 31 (1): 010401 .   DOI: 10.1088/0256-307X/31/1/010401
Abstract   PDF(pc) (355KB) ( 347 )
We propose a new law for the deceleration parameter that varies periodically with time. According to the law, we give a model of the oscillating universe with quintom matter in the framework of a 4-dimensional Friedmann–Robertson–Walker background. We find that, in the model, the Hubble parameter oscillates and keeps positive. The universe undergoes decelerating expansion and accelerating expansion alternately without singularity.
The Decoupling of Scalar-Modes from a Linearly Perturbed Dust-Filled Bianchi Type-I Model
Bob Osano
Chin. Phys. Lett. 2014, 31 (1): 010402 .   DOI: 10.1088/0256-307X/31/1/010402
Abstract   PDF(pc) (399KB) ( 226 )
We study linear perturbations about a dust filled Bianchi type-I model with the vorticity set to zero. In comparison to linear perturbations about the Friedmann–Lema?tre–Robertson–Walker models, modes of perturbations about the Bianchi type-I models are coupled. We find that the tensor that represents the background shear needs to be degenerate in order for the scalar-mode perturbations to decouple from the rest of the flow.
Emission of Phonons from a Rotating Sonic Black Hole
FANG Heng-Zhong, ZHOU Kai-Hu
Chin. Phys. Lett. 2014, 31 (1): 010403 .   DOI: 10.1088/0256-307X/31/1/010403
Abstract   PDF(pc) (432KB) ( 264 )
We investigate the Hawking radiation from a rotating acoustic black hole. The phonon emission is calculated by using two methods and the same results are obtained. The contribution of the time coordinate to the phonon radiation is also discussed, which cannot be ignored for the coordinate systems that are not well-behaved at the horizon.
A Comparative Study on the Self Diffusion of N-Octadecane with Crystal and Amorphous Structure by Molecular Dynamics Simulation
RAO Zhong-Hao, LIU Xin-Jian, ZHANG Rui-Kai, LI Xiang, WEI Chang-Xing, WANG Hao-Dong, LI Yi-Min
Chin. Phys. Lett. 2014, 31 (1): 010501 .   DOI: 10.1088/0256-307X/31/1/010501
Abstract   PDF(pc) (791KB) ( 481 )
The straight chain n-alkanes and their mixture, which can be used as phase change materials (PCM) for thermal energy storage, have attracted much attention in recent years. We employ the molecular dynamics (MD) simulation to investigate their thermophysical properties, including self diffusion and melting of n-octadecane with crystal and amorphous structures. Our results show that, although the initial and melted structures of n-octadecane with crystal and amorphous are different, the melting behaviors of n-octadecane judged by the self diffusion behavior are consistent. The MD simulation indicates that both the crystal and amorphous structures are effective for the property investigation of n-octadecane and the simulated conclusion can be used as reference for modeling the alkanes-based PCM system.
State Transition Induced by Self-Steepening and Self Phase-Modulation
HE Jing-Song, XU Shu-Wei, M. S. Ruderman, R. Erdélyi
Chin. Phys. Lett. 2014, 31 (1): 010502 .   DOI: 10.1088/0256-307X/31/1/010502
Abstract   PDF(pc) (741KB) ( 279 )
We present a rational solution for a mixed nonlinear Schr?dinger (MNLS) equation. This solution has two free parameters, a and b, representing the contributions of self-steepening and self phase-modulation (SPM) of an associated physical system, respectively. It describes five soliton states: a paired bright-bright soliton, a single soliton, a paired bright-grey soliton, a paired bright-black soliton, and a rogue wave state. We show that the transition among these five states is induced by self-steepening and SPM through tuning the values of a and b. This is a unique and potentially fundamentally important phenomenon in a physical system described by the MNLS equation.
Methodological Study on AMS Measurement of U Isotope Ratios in Nanogram U Samples
DONG Ke-Jun, WANG Chen, HE Ming, LIN De-Yu, ZHAO Xing-Hong, LI Li-Li, ZHAO Yong-Gang, DOU Liang, XIE Lin-Bo, WU Shao-Yong, YIN Xin-Yi, WANG Xiang-Gao, SHEN Hong-Tao, YOU Qu-Bo, JIANG Shan
Chin. Phys. Lett. 2014, 31 (1): 010701 .   DOI: 10.1088/0256-307X/31/1/010701
Abstract   PDF(pc) (520KB) ( 604 )
The determination of uranium isotopic composition in trace samples is important in different fields. A new measurement method that uses an accelerator mass spectrometry (AMS) technique has been developed for the analysis of uranium isotopic ratios in ultra-trace uranium samples at the China Institute of Atomic Energy. As a result, about 5-nanogram level uranium samples analyzed with AMS is achieved.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Tetraneutron in the Chiral Quark Model
MENG Nan, LI Bo-Lin, PING Jia-Lun
Chin. Phys. Lett. 2014, 31 (1): 011201 .   DOI: 10.1088/0256-307X/31/1/011201
Abstract   PDF(pc) (587KB) ( 251 )
The tetraneutron state is studied in the framework of the chiral quark model with tetrahedron configuration. The universal attraction property of σ-meson exchange leads to a strong attraction in the effective potential of the system. It is possible to form a bound state. For comparison, the naive quark model is also employed to carry out the calculation. A weak attraction, which is too weak to bind the system, is obtained.
Photoproduction of Light Vector Meson in Relativistic Heavy Ion Collisions
YU Gong-Ming, LI Yun-De
Chin. Phys. Lett. 2014, 31 (1): 011202 .   DOI: 10.1088/0256-307X/31/1/011202
Abstract   PDF(pc) (549KB) ( 267 )
We calculate the hard photoproduction of light vector meson from the fragmentation of photon in Pb–Pb collisions. Using the perturbative quantum chromodynamics calculation, we rigorously derive the electromagnetic fragmentation production for ρ, ω and φ in relativistic nucleus-nucleus collisions by the photoproduction processes. It is shown that the differential cross section of photoproduction processes of light vector meson cannot be negligible in relativistic heavy ion collisions at Large Hadron Collider energies.
Enhanced Correlation of Electron-Positron Pair in Two and Three Dimensions
TANG Suo, XIE Bai-Song, WANG Hong-Yu, LIU Jie, FU Li-Bin, YU Ming-Young
Chin. Phys. Lett. 2014, 31 (1): 011203 .   DOI: 10.1088/0256-307X/31/1/011203
Abstract   PDF(pc) (919KB) ( 270 )
Early time electron-positron correlation in vacuum pair-production in an external field is investigated. The entangled electron and positron wave functions are obtained analytically in the configuration and momentum spaces. It is shown that, relative to that of the one-dimensional theory, two- and three-dimensional calculations yield enhanced spatial correlation and broadened momentum spectra. In fact, at early times the electron and positron almost coincide spatially. The correlation also depends on the direction of the applied field. For the spatial correlation, the transverse correlation is stronger than the longitudinal correlation.
The Prediction of Possible Nonstrange Dibaryon
DAI Lian-Rong
Chin. Phys. Lett. 2014, 31 (1): 011401 .   DOI: 10.1088/0256-307X/31/1/011401
Abstract   PDF(pc) (567KB) ( 210 )
Recently, the mixing of scalar mesons was introduced into the chiral SU(3) quark model and also dynamically applied to the baryon-baryon system. The results show that the nucleon-nucleon and hyperon-nucleon scattering data can be reasonably described for different mixing cases, one is ideal mixing and the other is θs=19° mixing. In the present work, by taking the above parameters, the possible candidate of deltaron bound state is further predicted. We find that the contributions from σ and ε exchange to binding energy of deltaron are different, that the contribution from ε exchange is negligible, and that σ exchange is dominant. We also find that the binding energy of deltaron is very stable, around several tens of MeV, no matter what kind of mixing is adopted.
NUCLEAR PHYSICS
Three-Body Calculation of the 4He(3H,γ)7Li and 4He(3He,γ)7Be Reactions and Structure of the 7Li and 7Be at Solar Energies
H. Sadeghi, H. Khalili
Chin. Phys. Lett. 2014, 31 (1): 012101 .   DOI: 10.1088/0256-307X/31/1/012101
Abstract   PDF(pc) (495KB) ( 286 )
The two 3H+4He and 3He+4He fusion reactions at low energies are usually viewed as an approximate external capture process. We study the 4He(3H,γ)7Li and 4He(3He,γ)7Be reactions in a cluster model, which can take into account two- and three-body electromagnetic currents, using minimal substitution in the explicit momentum dependence of the two- and three-cluster interactions. Our main goal is to explore how the cross section of the low-energy 3H+4He or 3He+4He capture reactions depends on energy. The astrophysical S-factors for these reactions are calculated at very low energies. We construct the conserved realistic Argonne v18 for two nucleons and Urbana IX or Tucson-Melbourne three-cluster interactions, which are considered for calculation. We also calculate the binding energies and the structural properties of 3H+4He or 3He+4He systems. The binding energies are found to be ?37.72 (?36.32) MeV and ?39.35 (?37.43) MeV, with (without) three-body interactions for 7Be and 7Li, in satisfactory agreement with other theoretical results and experimental data, respectively.
Dosimetry Methods of Fast Neutron Using the Semiconductor Diodes
H. Zaki Dizaji, T. Kakavand, F. Abbasi Davani
Chin. Phys. Lett. 2014, 31 (1): 012901 .   DOI: 10.1088/0256-307X/31/1/012901
Abstract   PDF(pc) (683KB) ( 277 )
Semiconductor detectors based on a silicon pin diode are frequently used in the detection of different nuclear radiations. For the detection and dosimetry of fast neutrons, these silicon detectors are coupled with a fast neutron converter. Incident neutrons interact with the converter and produce charged particles that can deposit their energy in the detectors and produce a signal. In this study, three methods are introduced for fast neutron dosimetry by using the silicon detectors, which are: recoil proton spectroscopy, similarity of detector response function with conversion function, and a discriminator layer. Monte Carlo simulation is used to calculate the response of dosimetry systems based on these methods. In the different doses of an 241Am-Be neutron source, dosimetry responses are evaluated. The error values of measured data for dosimetry by these methods are in the range of 15–25%. We find fairly good agreement in the 241Am-Be neutron sources.
A Novel Method for Rigorously Analyzing Beam Loading Effect Based on the Macro-Particle Model
CHEN Qu-Shan, PEI Yuan-Ji, HU Tong-Ning, QIN Bin
Chin. Phys. Lett. 2014, 31 (1): 012902 .   DOI: 10.1088/0256-307X/31/1/012902
Abstract   PDF(pc) (1216KB) ( 295 )
The beam loading effect is a considerable issue for a high average current beam. We apply a novel method without utilizing the specious beam current value to rigorously analyze the beam loading effect in S-band linacs. By tracking every macro-particle's state and using the energy conservation law, power dissipated from the beam is calculated in each cell. In the new particle-based algorithm, the concept of equivalent beam current is proposed. Its value is not constant and it has a small variation through the accelerating structure. Also, we introduce the iteration algorithm as comparison and we find that the two algorithms coincide with each other very well.
ATOMIC AND MOLECULAR PHYSICS
An Analytical Derivation of a Symmetric Peak with Width Narrower than the Peak Width of the Probing Laser
XIE Feng, LI Dan, JIA Feng-Dong, ZHONG Zhi-Ping
Chin. Phys. Lett. 2014, 31 (1): 013201 .   DOI: 10.1088/0256-307X/31/1/013201
Abstract   PDF(pc) (571KB) ( 235 )
This work provides an analytical derivation that a symmetric peak with a width narrower than that of the probing laser can appear due to the non-coherent superposition of two Fano-type peaks.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Broadband Optical Active Waveguides Written by Femtosecond Laser Pulses in Lithium Fluoride
Ismael Chiamenti, Francesca Bonfigli, Anderson S. L. Gomes, Rosa Maria Montereali, Larissa N. da Costa, Hypolito J. Kalinowski
Chin. Phys. Lett. 2014, 31 (1): 014201 .   DOI: 10.1088/0256-307X/31/1/014201
Abstract   PDF(pc) (963KB) ( 274 )
Broadband waveguiding through light-emitting strips directly written in a blank lithium fluoride crystal with a femtosecond laser is reported. Light guiding was observed at several optical wavelengths, from blue, 458 nm, to near-infrared, at 1550 nm. Visible photoluminescence spectra of the optically active F2 and F3+ color centers produced by the fs laser writing process were measured. The wavelength-dependent refractive index increase was estimated to be in the order of 10?3–10?4 in the visible and near-infrared spectral intervals, which is consistent with the stable formation of point defects in LiF.
Transmission Characteristics of Waveguide-Coupled Nanocavity Embedded in Two Atoms with Dipole-Dipole Interaction
CHENG Mu-Tian, MA Xiao-San, WANG Xia
Chin. Phys. Lett. 2014, 31 (1): 014202 .   DOI: 10.1088/0256-307X/31/1/014202
Abstract   PDF(pc) (685KB) ( 307 )

Photon scattering properties in one-dimensional waveguide side coupled to a nanocavity embedded in two atoms with dipole-dipole interaction (DDI) are investigated theoretically. The analytical expressions of the transmission and reflection amplitudes are deduced by using the real-space Hamiltonian. A method to determine the coupling strength of DDI is proposed. Realization of single photon switching by modulation the DDI is investigated. The influence of dissipations on the performance of the single photon switching are exhibited. An asymmetric Fano-type resonance, which can be controlled by the DDI, appears in the transmission spectrum.

Demonstration of Color Separation with 2ω KDP Wedge in High Power Laser Facilities
WANG Fang, LI Fu-Quan, HAN Wei, FENG Bin, ZHOU Li-Dan, JIA Huai-Ting, CAO Hua-Bao
Chin. Phys. Lett. 2014, 31 (1): 014203 .   DOI: 10.1088/0256-307X/31/1/014203
Abstract   PDF(pc) (503KB) ( 240 )
A 2ω wedge design is proposed with KDP crystal to disperse the unconverted light away from the target in a high power laser facility for inertial confinement fusion. The ultraviolet B-integral problem is released, and about 1.2 times in color separation angle is achieved according to both theoretical and experimental investigations when compared with conventional 3ω wedge. The frequency conversion efficiency is unaffected when the wedge is along the non-sensitive axis of the tripler.
An Easily Switchable Dual-Wavelength Passively Mode-Locked Erbium Fiber Laser
HUANG Hui-Chang, YANG Tong, YUAN Xiao-Zhi, YANG Zhong-Min
Chin. Phys. Lett. 2014, 31 (1): 014204 .   DOI: 10.1088/0256-307X/31/1/014204
Abstract   PDF(pc) (569KB) ( 349 )
A simple scheme of switchable dual-wavelength passively mode-locked fiber laser is demonstrated. The laser can be flexibly switched among different mode-locked states simply by tuning the cavity loss while keeping all the other cavity parameters fixed. As the cavity loss increases, the mode-locked fiber laser operates at the long-wavelength, dual-wavelength, and short-wavelength states, successively. In addition, these states can be conveniently switched without losing the mode-locked operation and the switching process is reversible as the cavity loss decreases. The mechanism is qualitatively explained by the balance between the fiber gain and the cavity loss.
Competition between Two Six-Wave Mixing Channels in Atomic Rb Vapor
ZHU Chang-Jun, TONG Na, HE Jun-Fang, ZHANG Guo-Qing, ZHAI Xue-Jun, XUE Bing
Chin. Phys. Lett. 2014, 31 (1): 014205 .   DOI: 10.1088/0256-307X/31/1/014205
Abstract   PDF(pc) (477KB) ( 234 )
Two six-wave mixing processes are achieved simultaneously in rubidium vapor and two channels are identified. Signal competition between the two channels is observed and phase matching conditions are analyzed for the two channels. The results show that the two six-wave mixing channels correspond to two parametric processes with weak coupling and, moreover, quantum interference and phase matching conditions primarily govern the signal competition.
Modulation of Junction Defects Created by Crossing Photonic Crystal Waveguides
LIN Xu-Sheng, LIU Jing-Lin, ZHENG Yun-Bao, LAN Sheng
Chin. Phys. Lett. 2014, 31 (1): 014206 .   DOI: 10.1088/0256-307X/31/1/014206
Abstract   PDF(pc) (765KB) ( 274 )
In optical circuits, functional elements are often placed on waveguide junctions. We show that a junction in photonic crystals (PCs) possesses localized modes very close to the bandpass of waveguides. Their mode resonances and field patterns can be controlled by modulating the PC waveguides. It is expected that functions such as switching and routing could be developed naturally by using junction modes without any special design of microcavities. Our calculation results can be explained by the coupled mode theory.
Generation of Femtosecond Laser Pulse at 1053 nm with Contrast of 10−11 by Optical-Parametric Amplification
SHEN Zhong-Wei, WANG Zhao-Hua, ZHANG Wei, FAN Hai-Tao, TENG Hao, WEI Zhi-Yi
Chin. Phys. Lett. 2014, 31 (1): 014207 .   DOI: 10.1088/0256-307X/31/1/014207
Abstract   PDF(pc) (771KB) ( 302 )
A high contrast 1053 nm femtosecond laser pulse with free background is demonstrated based on non-collinear optical-parametric amplification (NOPA). By permuting the signal and idler in two stages of NOPAs, 48.2 fs, 62 μJ laser pulse at 1053 nm with contrast ratio of 2.3×10?11 is obtained within the time scale of sub-5 ps. The beam quality factors M2 for tangential and sagittal directions are 1.59 and 1.30, respectively. This work not only proves a feasible way to generate a clean femtosecond laser pulse but can also be employed as an ideal frontend for ultrashort ultrahigh intensity Nd:glass-based laser systems.
Efficient Generation of Squeezed Light Based on MgO-Doped Periodically Poled LiNbO3
KONG De-Huan, LI Zong-Yang, WANG Xu-Yang, LI Yong-Min
Chin. Phys. Lett. 2014, 31 (1): 014208 .   DOI: 10.1088/0256-307X/31/1/014208
Abstract   PDF(pc) (663KB) ( 326 )
We demonstrate a high-efficiency green light conversion from an external cavity second harmonic generation with a MgO-doped periodically poled LiNbO3 crystal. The frequency doubler can reach a conversion efficiency of 64% with a fundamental power of 26 mW. Meanwhile, the generated green light is quadrature-amplitude squeezed and 1.2 dB green light squeezing is experimentally measured. The squeezing at different pump levels is also investigated and is in good agreement with the theoretical prediction.
Design and Fabrication of Six-Channel Complex-Coupled DFB Quantum Cascade Laser Arrays Based on a Sampled Grating
YAN Fang-Liang, ZHANG Jin-Chuan, YAO Dan-Yang, TAN Song, LIU Feng-Qi, WANG Li-Jun, WANG Zhan-Guo
Chin. Phys. Lett. 2014, 31 (1): 014209 .   DOI: 10.1088/0256-307X/31/1/014209
Abstract   PDF(pc) (685KB) ( 270 )
We designed and fabricated a six-channel complex-coupled distributed feedback (DFB) quantum cascade laser arrays based on a sampled Bragg grating. The six-channel DFB laser arrays exhibit a linear tuning range of 74 nm centered at a wavelength of 7.55 μm at room temperature. Robust single-mode emission with a side mode suppression ratio about 20 dB was observed, even at full power. The used sampled grating and reflectivity coating on the back facet lead to the peak output power varying from 55 to 82 mW with a small difference in slope efficiency from 100 to 128 mW/A.
Numerical Simulation of Droplets Impacting on a Liquid Film with a Vapor Bubble Growing
HOU Yan, TAO Yu-Jia, HUAI Xiu-Lan
Chin. Phys. Lett. 2014, 31 (1): 014701 .   DOI: 10.1088/0256-307X/31/1/014701
Abstract   PDF(pc) (1141KB) ( 398 )
A numerical model of multiphase flow is developed to investigate the relative contributions of droplet parameters to spray cooling heat transfer. The 2-D model takes into account the effects of surface tension, gravity and viscosity. The heat and mass exchanges of free surface are defined to study vapor bubble behavior in liquid films. The multiphase flow and heat transfer are discussed for the three droplet parameters: initial droplet position, initial droplet temperature, and droplet impact frequency. The heat transfer mechanisms of the three cases are discussed in detail.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Ferroelectric Transition and Curie–Weiss Behavior in Some Filled Tungsten Bronze Ceramics
ZHU Xiao-Li, CHEN Xiang-Ming
Chin. Phys. Lett. 2014, 31 (1): 015201 .   DOI: 10.1088/0256-307X/31/1/015201
Abstract   PDF(pc) (825KB) ( 653 )
Ferroelectric transitions in filled tungsten bronze ceramics Sr4R2Ti4Nb6O30, Sr5RTi3Nb7O30 (R=La, Nb, Sm & Eu) and Ba4Nd2Ti4Nb6O30 are investigated with differential scanning calorimetry (DSC) and the Curie–Weiss law fitting to the dielectric constant. The magnitude of the Curie–Weiss constant C~105 suggests displacement-type ferroelectric transition in the present compounds. The large ΔT difference between dielectric maximum temperature Tm and Curie–Weiss temperature T0) values indicate the difficult formation of ferroelectric domains or polar nanoregions in the present compounds and also the characteristics of the first order ferroelectric transition. Three categories are suggested for the ferroelectric transition in the above tungsten bronzes. The ferroelectric transition exhibits large thermal hysteresis. According to the DSC results, gradual recovery of the endothermic peak occurs after aging at temperature below the Curie point, indicating the gradual stability of the ferroelectric phase after cooling from the high-temperature para-electric phase. The relationship between the Curie–Weiss law fitting parameters and the nature of the ferroelectric transition is modified for the filled tungsten bronzes.
Self-Organized Micro-Columns and Nano-Spheres Generated by Pulsed Laser Ablation of Ti/Al Alloy in Water
CUI Qing-Qiang, LIU Xiang-Dong, CHEN Ming, ZHAO Ming-Wen, WANG Chun-Sheng, LI Shuang
Chin. Phys. Lett. 2014, 31 (1): 015202 .   DOI: 10.1088/0256-307X/31/1/015202
Abstract   PDF(pc) (1096KB) ( 271 )
Dense arrays of micro-columns are formed on the surface of Ti-Al alloy by cumulative nanosecond pulsed laser ablation in water. The fabric-like structure characterized by Ti-Al nano-spheres absorbed on micro-cluster in liquid is most likely responsible for the occurrence of laser micro-etching and localized melting, resulting in continuous deepening of micro-holes and the formation of micro-columns. Laser induced plasma spectroscopy is carried out to reveal the effect of micro-columns on subsequent pulse laser ablation. The intensity of spectral lines from Ti ions by additional laser ablation of the modified spot is higher than that created over a smooth surface. These results suggest that the micro-columns lead to an enhanced absorption of the following laser energy. The proposed results and relevant discussions are of importance for the development of light-trapping coatings on a metal surface.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Mobility Enhancement and Gate-Induced-Drain-Leakage Analysis of Strained-SiGe Channel p-MOSFETs with Higher-κ LaLuO3 Gate Dielectric
YU Wen-Jie, ZHANG Bo, LIU Chang, XUE Zhong-Ying, CHEN Ming, ZHAO Qing-Tai
Chin. Phys. Lett. 2014, 31 (1): 016101 .   DOI: 10.1088/0256-307X/31/1/016101
Abstract   PDF(pc) (718KB) ( 325 )
A strained-SiGe p-channel metal-oxide-semiconductor-field-effect transistors (p-MOSFETS) with higher-κ LaLuO3 gate dielectric was fabricated and electrically characterized. The novel higher-κ (κ30) gate dielectric, LaLuO3, was deposited by molecular-beam deposition and shows good quality for integration into the transistor. The transistor features good output and transfer characteristics. The hole mobility was extracted by the splitting CV method and a value of 200 cm2/V?s was obtained for strong inversion conditions, which indicates that the hole mobility is well enhanced by SiGe channel and that the LaLuO3 layer does not induce additional significant carrier scattering. Gate induced drain leakage is measured and analyzed by using an analytical model. Band-to-band tunneling efficiencies under high and low fields are found to be different, and the tunneling mechanism is discussed.
Correlation of Lithium Ionic Diffusion with Nb Concentration in Li7−xLa3Zr2−xNbxO12 Evaluated by an Internal Friction Method
XIA Yu, WANG Xian-Ping, GAO Yun-Xia, HU Jing, ZHUANG Zhong, GUO Li-Jun, FANG Qian-Feng, LIU Chang-Song
Chin. Phys. Lett. 2014, 31 (1): 016201 .   DOI: 10.1088/0256-307X/31/1/016201
Abstract   PDF(pc) (951KB) ( 289 )
Solid lithium-ion conductors Li7?xLa3Zr2?xNbxO12 (x=0.25, 0.5, 1, 1.5) with cubic garnet structure are successfully prepared by a solid state reaction method, and the effects of Nb concentration on lithium ion diffusion are investigated by means of internal friction (IF) technique. A prominent relaxation-type IF peak (actually composed of two components) is observed in each Nb doped Li7La3Zr2O12 compound: with apeak PL at lower temperature and a peak PH at higher temperature. The mechanisms of the two components are suggested to be associated with two diffusion processes of lithium ions via vacancies: 48g?48g and 48g?24 d. The relaxational strength of the IF peak gradually decreases, which is accompanied by the activation energy increasing from 0.45 eV to 0.64 eV with the increasing Nb doping level. The corresponding mechanism is ascribed to originate from lattice contraction as well as the lower concentration of diffusion ions induced by the substitution of Zr4+ by Nb5+.
Theoretical Study of Thermodynamics Properties and Bulk Modulus of SiC under High Pressure and Temperature
ZHANG Xu-Dong, CUI Shou-Xin, SHI Hai-Feng
Chin. Phys. Lett. 2014, 31 (1): 016401 .   DOI: 10.1088/0256-307X/31/1/016401
Abstract   PDF(pc) (820KB) ( 211 )
In extended pressure and temperature ranges, a theoretical study of the isothermal bulk modulus of SiC in B3 structure under high pressure and temperature is carried out by means of first-principles density functional theoretical calculations combined with the quasi-harmonic Debye model. Through the quasi-harmonic Debye model, the isothermal bulk modulus and its first and second pressure derivatives are successfully obtained. The thermodynamics properties of 3C-SiC are investigated in the pressure range of 0–100 GPa and the temperature range of 0–2000 K.
Theoretical Study on Equation of State of Porous Mo and Sn
SONG Hai-Feng, TIAN Ming-Feng, LIU Hai-Feng, SONG Hong-Zhou, ZHANG Gong-Mu
Chin. Phys. Lett. 2014, 31 (1): 016402 .   DOI: 10.1088/0256-307X/31/1/016402
Abstract   PDF(pc) (599KB) ( 229 )
We present a first-principles scheme to investigate the equation of state (EOS) of porous materials, based on our recently developed modified mean-field potential approach. By taking the effect of the structural parameters on the free energy into account, we calculate the total energy of materials with initial different densities and then study the EOS of porous Mo and Sn as a prototype. The calculated results are in good agreement with the experimental data available, which demonstrates that our scheme is suitable for investigating EOS of porous materials over a wide range of porosities and pressures.
In Situ X-Ray Diffraction Study on Surface Melting of Bi Nanoparticles Embedded in a SiO2 Matrix
CHEN Xiao-Ming, HUO Kai-Tuo, LIU Peng
Chin. Phys. Lett. 2014, 31 (1): 016403 .   DOI: 10.1088/0256-307X/31/1/016403
Abstract   PDF(pc) (845KB) ( 236 )
Bi nanoparticles embedded in a SiO2 matrix were prepared via the high energy ball milling method. The melting behavior of Bi nanoparticles was studied by means of differential scanning calorimetry (DSC) and high-temperature in situ X-ray diffraction (XRD). DSC cannot distinguish the surface melting from 'bulk' melting of the Bi nanoparticles. The XRD intensity of the Bi nanoparticles decreases progressively during the in situ heating process. The variation in the normalized integrated XRD intensity versus temperature is related to the average grain size of Bi nanoparticles. Considering the effects of temperature on Debye–Waller factor and Lorentz-polarization factor, we discuss the XRD results in accordance with surface melting. Our results show that the in situ XRD technique is effective to explore the surface melting of nanoparticles.
Thermal Conductivity of the Partly Covered Inner Tube in a Double-Walled Carbon Nanotube with Varied Coverage Ratios
PAN Rui-Qin, XU Zi-Jian, DAI Cui-Xia
Chin. Phys. Lett. 2014, 31 (1): 016501 .   DOI: 10.1088/0256-307X/31/1/016501
Abstract   PDF(pc) (480KB) ( 291 )
We present a study of the thermal conductivity of a partly covered inner tube in a double-walled carbon nanotube with varied covering ratios using a non-equilibrium molecular dynamics method. Our results show that the thermal conductivity of the inner tube changes non-linearly and non-monotonically with the increasing coverage ratio, forming a V-shaped curve. Minimal conductivity occurs at the coverage ratio of 58%, with its value being 69% of the maximal conductivity, which appears in the full coverage case. We analyze three mutually competitive mechanisms that result in this thermal conductivity behavior with the assistance of a phonon spectrum calculation.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Density-Functional Theory Investigation of Sr2CrOsO6 with Cubic Symmetry Using Modified Becke–Johnson Potential
GUO San-Dong
Chin. Phys. Lett. 2014, 31 (1): 017101 .   DOI: 10.1088/0256-307X/31/1/017101
Abstract   PDF(pc) (574KB) ( 327 )
We investigate the electronic structures and optical dielectric functions of the high temperature phase of Sr2CrOsO6 with cubic structure by using Tran and Blaha's modified Becke and Johnson exchange potential. In the absence of spin-orbit coupling, the total spin moment is 0μB. When spin-orbit coupling is included, the small total spin moment and an unquenched Os orbital moment appear, and the spin non-conservation gap becomes smaller. The calculated net magnetic moment is smaller than the popular generalized gradient approximation result, and the spin non-conservation gap is larger. The optical dielectric functions with spin-orbit coupling are not very different from the ones without spin-orbit coupling.
Trapping Behavior of He in Ti Revisited by ab initio Calculations
WAN Chu-Bin, ZHOU Xiao-Song, LI Shi-Na, ZHANG Hui-Jun, LIANG Jian-Hua, PENG Shu-Ming, JU Xin
Chin. Phys. Lett. 2014, 31 (1): 017102 .   DOI: 10.1088/0256-307X/31/1/017102
Abstract   PDF(pc) (717KB) ( 273 )
We report a detailed ab initio study of the trapping behavior of interstitial helium atoms (IHAs) in hcp Ti. The tetrahedral interstitial site for one He is confirmed to be the most stable IHA configuration, but the most favorable interstitial site comprises two adjacent octahedral sites for two helium atoms. The octahedral IHA can trap another IHA regardless of the site where it is initially located, whereas the tetrahedral IHA cannot. Hybridization among the different states is responsible for the stable order, which has significant implications for He clustering and bubble nucleation that can affect material performance in future fusion reactors. These results provide the basis for the development of improved atomistic models.
A New Perspective to Study the Correlation Effect of the Three-Dimensional Electron Gas
YU Zhi-Ming, LIU Yu-Liang
Chin. Phys. Lett. 2014, 31 (1): 017103 .   DOI: 10.1088/0256-307X/31/1/017103
Abstract   PDF(pc) (478KB) ( 247 )
The phase field, which originates from the electronic interaction, plays an important role in describing a strongly correlated system in one dimension. However, in higher dimensions the effect of phase field cannot be obviously understood. With the eigenfunctional theory, we calculate the pair distribution function of the three-dimensional electron gas to study the relationship between the phase field and the electronic correlation effect and show that at zero temperature the correlation effect of the electrons is mainly dominated by the phase fluctuation, which is produced by the electronic interaction. We also discuss the failure of random phase approximation in studying the correlation function when the correlation effect is strong in the view of the phase field.
Direct Observation of High-Temperature Superconductivity in One-Unit-Cell FeSe Films
ZHANG Wen-Hao, SUN Yi, ZHANG Jin-Song, LI Fang-Sen, GUO Ming-Hua, ZHAO Yan-Fei, ZHANG Hui-Min, PENG Jun-Ping, XING Ying, WANG Hui-Chao, FUJITA Takeshi, HIRATA Akihiko, LI Zhi, DING Hao, TANG Chen-Jia, WANG Meng, WANG Qing-Yan, HE Ke, JI Shuai-Hua, CHEN Xi, WANG Jun-Feng, XIA Zheng-Cai, LI Liang, WANG Ya-Yu, WANG Jian, WANG Li-Li, CHEN Ming-Wei, XUE Qi-Kun, MA Xu-Cun
Chin. Phys. Lett. 2014, 31 (1): 017401 .   DOI: 10.1088/0256-307X/31/1/017401
Abstract   PDF(pc) (1801KB) ( 2382 )

We prepared one-unit-cell (1-UC) thick FeSe films on insulating SrTiO3 substrates with non-superconducting FeTe protection layers by molecular beam epitaxy for ex situ studies. By direct transport and magnetic measurements, we provide definitive evidence for high temperature superconductivity in the 1-UC FeSe films with an onset TC above 40 K and an extremely large critical current density JC1.7×106 A/cm2 at 2 K, which are much higher than TC8 K and JC104 A/cm2 for bulk FeSe, respectively. Our work may pave the way to enhancing and tailoring superconductivity by interface engineering.

Room-Temperature Magnetism Realized by Doping Fe into Ferroelectric LiTaO3
SONG Ying-Jie, ZHANG Qing-Hua, SHEN Xi, NI Xiao-Dong, YAO Yuan, YU Ri-Cheng
Chin. Phys. Lett. 2014, 31 (1): 017501 .   DOI: 10.1088/0256-307X/31/1/017501
Abstract   PDF(pc) (672KB) ( 324 )
We synthesize LiTa1?xFexO3 (LTFO) ceramics by the conventional solid-state reaction method. The samples remain single phase up to x=0.09. The magnetic measurements show that the doping of Fe successfully realizes ferromagnetism of LTFO at room temperature. The dielectric measurements indicate that LTFO is ferroelectric, similarly to LiTaO3 (LTO), but its ferroelectric Curie temperature seems to decrease with the increasing Fe content. By means of doping Fe ions into LTO, the coexistence of spontaneous electric polarization and spontaneous magnetic moment is realized at room temperature.
Spin-Wave Modes in Exchange-Coupled FePt/FeNi Bilayer Films
LI Shu-Fa, HE Pan, CHENG Chu-Yuan, ZHOU Shi-Ming, LAI Tian-Shu
Chin. Phys. Lett. 2014, 31 (1): 017502 .   DOI: 10.1088/0256-307X/31/1/017502
Abstract   PDF(pc) (672KB) ( 324 )
A simple magnetic modulation structure of the exchange-coupling FePt/FeNi bilayer film is fabricated and studied for its magnetization dynamics using time-resolved magneto-optical polar Kerr spectroscopy. It is found that two spin-wave modes can be excited. One is fixed at 3.2 GHz in frequency for any external field and may serve as a frequency-stabilized spin-wave filter, while the other is external field dependent. In contrast, only the external field-dependent mode is excited in single-layer FeNi, supporting the localized origin of the mode at 3.2 GHz, which is confined to a thin exchange-coupling region. The other external field-dependent mode in frequency is attributed to the Kittel mode.
Magnetostatic Coupling in Ba0.8Sr0.2TiO3/CoFe2O4 Magnetoelectric Composite Thin Films of 2-2-Type Structure
RAO Wei, WANG Yun-Bo, WANG Ye-An, GAO Jun-Xiong, ZHOU Wen-Li, YU Jun
Chin. Phys. Lett. 2014, 31 (1): 017503 .   DOI: 10.1088/0256-307X/31/1/017503
Abstract   PDF(pc) (949KB) ( 296 )
Ba0.8Sr0.2TiO3/CoFe2O4 (BST/CFO) magnetoelectric composite thin films of 2-2-type structures are prepared onto Pt/Ti/SiO2/Si substrates by a sol-gel process and spin coating technique. The structure of the prepared thin film is substrate/BST/CFO/.../CFO/BST. Three CFO ferromagnetic layers are separated from each other by a thin BST layer. The upper CFO layer is magnetostatically coupled with the lower CFO layer. Subsequent scanning electron microscopy investigations show that the prepared thin films exhibit good morphologies and have a compact structure, and the cross-sectional micrographs clearly display a multilayered nanostructure of multilayered thin films. The composite thin films exhibit good magnetic and ferroelectric properties. The spacing between ferromagnetic layers can be varied by adjusting the thickness of intermediate BST layer. It is found that the strength of magnetostatic coupling has a great impact on magnetoelectric properties of composite thin film; that is, the magnetoelectric voltage coefficient of the composite thin film tends to increase with the decrease of pacing between two neighboring CFO ferromagnetic layers as a result of magnetostatic coupling effect.
Strain Induced Metastable Phase and Phase Revolution in PbTiO3-CoFe2O4 Nanocomposite Film
HU Chuan-Sheng, LUO Zhen-Lin, SUN Xia, PAN Guo-Qiang, HE Qing, WEN Wen, ZHOU Xing-Tai, Ichiro Takeuchi, GAO Chen
Chin. Phys. Lett. 2014, 31 (1): 017701 .   DOI: 10.1088/0256-307X/31/1/017701
Abstract   PDF(pc) (1013KB) ( 306 )
An inter-component epitaxial strain-induced PbTiO3 metastable phase is observed in a PbTiO3-CoFe2O4 epitaxial composite film, corresponding to the dielectric anomaly reported previously. High-resolution synchrotron radiation X-ray diffraction and first principles calculation demonstrate the coexistence of different PbTiO3 phases, even a possible morphotropic phase boundary in the film, elucidating the underlying microscopic mechanism of the formation of PbTiO3 metastable phase. This sheds light on the design and manipulation of electromechanical properties of epitaxial films, through the strain engineering.
Terahertz Radiation from Graphite Excited by Femtosecond Laser Pulses
WU Zhong-An, WU Xiao-Jun, WANG Li
Chin. Phys. Lett. 2014, 31 (1): 017801 .   DOI: 10.1088/0256-307X/31/1/017801
Abstract   PDF(pc) (493KB) ( 268 )
We experimentally investigate the terahertz (THz) generation from a graphite surface induced by femtosecond laser pulses, and systematically study the dependence on the excitation power, the crystal orientation of graphite, polarization state and incident angle of optical beam. New evidence related to excitation and detection geometry is found and presented, which supports the THz generation mechanism of transient photocarrier transporting along the basal plane normal. Our observation also suggests other probable contributions by in-plane charge oscillations. The results may be helpful to explore and understand the photoelectric properties of graphite and other allotropes of carbon.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Near-Field Enhancement and Absorption Properties of Metal-Dielectric-Metal Microcavities in the Mid-Infrared Range
HENG Hang, YANG Li, YE Yong-Hong
Chin. Phys. Lett. 2014, 31 (1): 018101 .   DOI: 10.1088/0256-307X/31/1/018101
Abstract   PDF(pc) (842KB) ( 296 )
An important property of optical metamaterials is the ability to concentrate light into extremely tiny volumes, so as to enhance their interaction with quantum objects. In this work, we numerically study the near-field enhancement and absorption properties inside the cylindrical microcavities formed by a Au-GaAs-Au sandwiched structure. At normal incidence, the obtained reflection spectra show that the resonance wavelength of microcavities operates in the range of 5–5.8 μm. We also calculate the contrast C (C=1?Rmin), which can be increased to 97% by optimizing the structure's geometry parameters. Moreover, we demonstrate that the multilayer structure with sub-wavelength electromagnetic confinement allows 103–104-fold enhancement of the electromagnetic energy density inside the cavities, which contains the most energy of the incident electromagnetic radiation and has a higher quality factor Q, indicating a narrower linewidth for surface enhanced molecular absorption spectroscopy and the tracking of characteristic molecular vibrational modes in the mid-infrared region. The structure is insensitive to the polarization of the incident wave due to the symmetry of the cylindrical microcavities. The unique properties of the metal-dielectric-metal metamaterials will have potential applications in new plasmonic detectors, bio-sensing and solar cells, etc.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Photometric Calibration of the Barium Cloud Image in a Space Active Experiment: Determining the Release Efficiency
XIE Liang-Hai, LI Lei, WANG Jing-Dong, TAO Ran, CHENG Bing-Jun, ZHANG Yi-Teng
Chin. Phys. Lett. 2014, 31 (1): 019401 .   DOI: 10.1088/0256-307X/31/1/019401
Abstract   PDF(pc) (589KB) ( 315 )
The barium release experiment is an effective method to explore the near-earth environment and to study all kinds of space physics processes. The first space barium release experiment in China was successfully carried out by a sounding rocket on April 5, 2013. This work is devoted to calculating the release efficiency of the barium release by analyzing the optical image observed during the experiment. First, we present a method to calibrate the images grey value of barium cloud with the reference stars to obtain the radiant fluxes at different moments. Then the release efficiency is obtained by a curve fitting with the theoretical evolution model of barium cloud. The calculated result is basically consistent with the test value on ground.
47 articles