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Volume 34 Issue 7
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Resonance Analyses for a Noisy Coupled Brusselator Model
Pei-Rong Guo, Hai-Yan Wang, Jin-Zhong Ma
Chin. Phys. Lett. 2017, 34 (7): 070201 .   DOI: 10.1088/0256-307X/34/7/070201
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We discuss the dynamical behavior of a chemical network arising from the coupling of two Brusselators established by the relationship between products and substrates. Our interest is to investigate the coherence resonance (CR) phenomena caused by noise for a coupled Brusselator model in the vicinity of the Hopf bifurcation, which can be determined by the signal-to-noise ratio (SNR). The CR in two coupled Brusselators will be considered in the presence of the Gaussian colored noise and two uncorrelated Gaussian white noises. Simulation results show that, for the case of single noise, the SNR characterizing the degree of temporal regularity of coupled model reaches a maximum value at some optimal noise levels, and the noise intensity can enhance the CR phenomena of both subsystems with a similar trend but in different resonance degrees. Meanwhile, effects of noise intensities on CR of the second subsystem are opposite for the systems under two uncorrelated Gaussian white noises. Moreover, we find that CR might be a general phenomenon in coupled systems.
Bright-Dark Mixed $N$-Soliton Solution of the Two-Dimensional Maccari System
Zhong Han, Yong Chen
Chin. Phys. Lett. 2017, 34 (7): 070202 .   DOI: 10.1088/0256-307X/34/7/070202
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The general bright-dark mixed $N$-soliton solution of the two-dimensional Maccari system is obtained with the KP hierarchy reduction method. The dynamics of single and two solitons are discussed in detail. Asymptotic analysis shows that two solitons undergo elastic collision accompanied by a position shift. Furthermore, our analysis on mixed soliton bound states shows that arbitrary higher-order soliton bound states can take place.
Fermionic Covariant Prolongation Structure for a Super Nonlinear Evolution Equation in 2+1 Dimensions
Zhao-Wen Yan, Xiao-Li Wang, Min-Li Li
Chin. Phys. Lett. 2017, 34 (7): 070203 .   DOI: 10.1088/0256-307X/34/7/070203
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The integrability of a (2+1)-dimensional super nonlinear evolution equation is analyzed in the framework of the fermionic covariant prolongation structure theory. We construct the prolongation structure of the multidimensional super integrable equation and investigate its Lax representation. Furthermore, the Bäcklund transformation is presented and we derive a solution to the super integrable equation.
General Single-Mode Gaussian Operation with Two-Mode Entangled State
Shu-Hong Hao, Xian-Shan Huang, Dong Wang
Chin. Phys. Lett. 2017, 34 (7): 070301 .   DOI: 10.1088/0256-307X/34/7/070301
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Realizing the logic operations with small-scale states is pursued to improve the utilization of quantum resources and to simplify the experimental setup. We propose a scheme to realize a general single-mode Gaussian operation with a two-mode entangled state by utilizing only one nondegenerate optical parametric amplifier and by adjusting four angle parameters. The fidelity of the output mode can be optimized by changing one of the angle parameters. This scheme would be utilized as a basic efficient element in the future large-scale quantum computation.
Implementing Classical Hadamard Transform Algorithm by Continuous Variable Cluster State
Yu Wang, Qi Su
Chin. Phys. Lett. 2017, 34 (7): 070302 .   DOI: 10.1088/0256-307X/34/7/070302
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Measurement-based one-way quantum computation, which uses cluster states as resources, provides an efficient model to perform computation. However, few of the continuous variable (CV) quantum algorithms and classical algorithms based on one-way quantum computation were proposed. In this work, we propose a method to implement the classical Hadamard transform algorithm utilizing the CV cluster state. Compared with classical computation, only half operations are required when it is operated in the one-way CV quantum computer. As an example, we present a concrete scheme of four-mode classical Hadamard transform algorithm with a four-partite CV cluster state. This method connects the quantum computer and the classical algorithms, which shows the feasibility of running classical algorithms in a quantum computer efficiently.
Phase Dissipation of an Open Two-Mode Bose–Einstein Condensate
Yan-Na Li, Wei-Dong Li
Chin. Phys. Lett. 2017, 34 (7): 070303 .   DOI: 10.1088/0256-307X/34/7/070303
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We study the dynamics of a two-mode Bose–Hubbard model with phase dissipation, based on the master equation. An analytical solution is presented with nonzero asymmetry and phase noise. The effects of asymmetry and phase noise play a contrasting role in the dynamics. The asymmetry makes the oscillation fast, while phase noise enlarges the period. The conditions for the cases of fast decay and oscillation are presented. As a possible application, the dynamical evolution of the population for cold atomic gases with synthetic gauge interaction, which can be understood as two-mode dynamics in momentum space, is predicted.
Floquet Bound States in a Driven Two-Particle Bose–Hubbard Model with an Impurity
Hong-Hua Zhong, Zheng Zhou, Bo Zhu, Yong-Guan Ke, Chao-Hong Lee
Chin. Phys. Lett. 2017, 34 (7): 070304 .   DOI: 10.1088/0256-307X/34/7/070304
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We investigate how the driving field affects the bound states in the one-dimensional two-particle Bose–Hubbard model with an impurity. In the high-frequency regime, compared with the static lattice [Phys. Rev. Lett. 109 (2012) 116405], a new type of Floquet bound state can be obtained even for a weak particle–particle interaction by tuning the driving amplitude. Moreover, the localization degree of the Floquet bound molecular state can be adjusted by tuning the driving frequency, and even the Floquet bound molecular state can be changed into the Floquet extended state when the driving frequency is below a critical value. Our results provide an efficient way to manipulate bound states in the many-body systems.
A Four-Phase Improvement of Grover's Algorithm
Bo-Wen Ma, Wan-Su Bao, Tan Li, Feng-Guang Li, Shuo Zhang, Xiang-Qun Fu
Chin. Phys. Lett. 2017, 34 (7): 070305 .   DOI: 10.1088/0256-307X/34/7/070305
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When applying Grover's algorithm to an unordered database, the probability of obtaining correct results usually decreases as the quantity of target increases. A four-phase improvement of Grover's algorithm is proposed to fix the deficiency, and the unitary and the phase-matching condition are also proposed. With this improved scheme, when the proportion of target is over 1/3, the probability of obtaining correct results is greater than 97.82% with only one iteration using two phases. When the computational complexity is $O(\sqrt{M/N})$, the algorithm can succeed with a probability no less than 99.63%.
Accretion onto the Magnetically Charged Regular Black Hole
M. Azam, A. Aslam
Chin. Phys. Lett. 2017, 34 (7): 070401 .   DOI: 10.1088/0256-307X/34/7/070401
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We investigate the accretion process for static spherically symmetric geometry, i.e., magnetically charged regular black hole with isotropic fluid. We obtain generalized expressions for the velocity ($u(r)$), speed of sound ($c^2_{\rm s}$), energy density ($\rho(r)$) and accretion rate ($\dot{M}$) at the critical point near the regular black hole during the accretion process. We also plot these physical parameters against fixed values of charge, mass and different values of equation of state parameter to study the process of accretion. We find that radial velocity and energy density of the fluid remain positive and negative as well as rate of change of mass is increased and decreased for dust, stiff, quintessence fluid and phantom-like fluid, respectively.
A Unified Approach to the Thermodynamics and Quantum Scaling Functions of One-Dimensional Strongly Attractive $SU(w)$ Fermi Gases
Yi-Cong Yu, Xi-Wen Guan
Chin. Phys. Lett. 2017, 34 (7): 070501 .   DOI: 10.1088/0256-307X/34/7/070501
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We present a unified derivation of the pressure equation of states, thermodynamics and scaling functions for the one-dimensional (1D) strongly attractive Fermi gases with $SU(w)$ symmetry. These physical quantities provide a rigorous understanding on a universality class of quantum criticality characterized by the critical exponents $z=2$ and correlation length exponent $\nu=1/2$. Such a universality class of quantum criticality can occur when the Fermi sea of one branch of charge bound states starts to fill or becomes gapped at zero temperature. The quantum critical cone can be determined by the double peaks in specific heat, which serve to mark two crossover temperatures fanning out from the critical point. Our method opens to further study on quantum phases and phase transitions in strongly interacting fermions with large $SU(w)$ and non-$SU(w)$ symmetries in one dimension.
A High-Sensitivity Terahertz Detector Based on a Low-Barrier Schottky Diode
Xiao-Yu Liu, Yong Zhang, De-Jiao Xia, Tian-Hao Ren, Jing-Tao Zhou, Dong Guo, Zhi Jin
Chin. Phys. Lett. 2017, 34 (7): 070701 .   DOI: 10.1088/0256-307X/34/7/070701
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A low-barrier Schottky barrier diode based on the InGaAs/InP material system is designed and fabricated with a new non-destructive dry over-etching process. By using this diode, a high-sensitivity waveguide detector is proposed. The measured maximum responsivity is over 2000 mV/mW at 630 GHz. The measured noise effective power (NEP) is less than 35 pW/Hz$^{0.5}$ at 570–630 GHz. The minimum NEP is 14 pW/Hz$^{0.5}$ at 630 GHz. The proposed high-sensitivity waveguide detector has the characteristics of simple structure, compact size, low cost and high performance, and can be used in a variety of applications such as imaging, molecular spectroscopy and atmospheric remote sensing.
A Photonuclear Reaction Model Based on IQMD in Intermediate-Energy Region
Bo-Song Huang, Yu-Gang Ma
Chin. Phys. Lett. 2017, 34 (7): 072401 .   DOI: 10.1088/0256-307X/34/7/072401
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A photonuclear reaction transport model based on an isospin-dependent quantum molecular dynamics model (IQMD) is presented in the intermediate energy region, which is named as GiQMD in this study. Methodology to simulate the course of the photonuclear reaction within the IQMD frame is described to study the photo-absorption cross section and $\pi$ meson production, and the simulation results are compared with some available experimental data as well as the Giessen Boltzmann–Uehling–Uhlenbeck model.
Constructions and Preliminary HV Conditioning of a Photocathode Direct-Current Electron Gun at IHEP
Xiao-Ping Li, Jiu-Qing Wang, Jin-Qiang Xu, Shi-Lun Pei, Ou-Zheng Xiao, Da-Yong He, Kun Lv, Xiang-Cheng Kong, Xiao-Hua Peng
Chin. Phys. Lett. 2017, 34 (7): 072901 .   DOI: 10.1088/0256-307X/34/7/072901
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As one of the most important key technologies for future advanced light source based on the energy recovery linac, a photocathode dc electron gun is supported by Institute of High Energy Physics (IHEP) to address the technical challenges of producing very low emittance beams at high average current. Construction of the dc gun is completed and a preliminary high voltage conditioning is carried out up to 440 kV. The design, construction and preliminary HV conditioning results for the dc gun are described.
Theoretical Analysis of Rydberg and Autoionizing State Spectra of Antimony
Shuang-Fei Lv, Ruohong Li, Feng-Dong Jia, Xiao-Kang Li, Jens Lassen, Zhi-Ping Zhong
Chin. Phys. Lett. 2017, 34 (7): 073101 .   DOI: 10.1088/0256-307X/34/7/073101
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We calculate the Rydberg and autoionization Rydberg spectra of antimony (Sb) from first principles by relativistic multichannel theory within the framework of multichannel quantum defect theory. Our calculation can be used to classify and assign the atomic states described in recently reported three Rydberg series and four autoionizing states. The perturbation effects on line intensity, variation and line profile are discussed. Assignments of the perturber states and autoionizing states are presented.
State Preparation in a Cold Atom Clock by Optical Pumping
Yu-Xiong Duan, Bin Wang, Jing-Feng Xiang, Qian Liu, Qiu-Zhi Qu, De-Sheng Lü, Liang Liu
Chin. Phys. Lett. 2017, 34 (7): 073201 .   DOI: 10.1088/0256-307X/34/7/073201
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We implement optical pumping to prepare cold atoms in our prototype of the $^{87}$Rb space cold atom clock, which operates in the one-way mode. Several modifications are made on our previous physical and optical system. The effective atomic signal in the top detection zone is increased to 2.5 times with 87% pumping efficiency. The temperature of the cold atom cloud is increased by 1.4 $\mu$K. We study the dependences of the effective signal gain and pumping efficiency on the pumping laser intensity and detuning. The effects of $\sigma$ transition are discussed. This technique may be used in the future space cold atom clocks.
Ion Photon Emission Microscope for Single Event Effect Testing in CIAE
Yan-Wen Zhang, Gang Guo, Jian-Cheng Liu, Shu-Ting Shi, Ying-Can Qin, Li-Li Li, Lin-Feng He
Chin. Phys. Lett. 2017, 34 (7): 073401 .   DOI: 10.1088/0256-307X/34/7/073401
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Ion photon emission microscopy (IPEM) is a new ion-induced emission microscopy. It employs a broad ion beam with high energy and low fluence rate impinging on a sample. The position of a single ion is detected by an optical system with objective lens, prism, microscope tube and charge coupled device (CCD). A thin ZnS film doped with Ag ions is used as a luminescent material. Generation efficiency and transmission efficiency of photons in the ZnS(Ag) film created by irradiated Cl ions are calculated. A single Cl ion optical microscopic image is observed by high quantum efficiency CCD. The resolution of a single Cl ion given in this IPEM system is 6 μm. Several factors influencing the resolution are discussed. A silicon diode is used to collect the electrical signals caused by the incident ions. Effective and accidental coincidence of optical images and electronic signals are illustrated. A two-dimensional map of single event effect is drawn out according to the data of effective coincidence.
High Optical Magnification Three-Dimensional Integral Imaging of Biological Micro-organism
Dan Sun, Yao Lu, Jin-Bo Hao, Kai-Ge Wang
Chin. Phys. Lett. 2017, 34 (7): 074201 .   DOI: 10.1088/0256-307X/34/7/074201
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A high optical magnification three-dimensional imaging system is proposed using an optic microscope whose ocular (eyepiece) is retained and the structure of the transmission mode is not destroyed. The elemental image array is captured through the micro lens array. Due to the front diffuse transmission element, each micro lens sees a slightly different spatial perspective of the scene, and a different independent image is formed in each micro lens channel. Each micro lens channel is imaged by a Fourier lens and captured by a CCD. The design translating the stage in $x$ or $y$ provides no parallax. Compared with the conventional integral imaging of micro-objects, the optical magnification of micro-objects in the proposed system can enhanced remarkably. The principle of the enhancement of the image depth is explained in detail and the experimental results are presented.
Intracavity Spontaneous Parametric Down-Conversion in Bragg Reflection Waveguide Edge Emitting Diode
Si-Hang Wei, Xiang-Jun Shang, Ben Ma, Ze-Sheng Chen, Yong-Ping Liao, Hai-Qiao Ni, Zhi-Chuan Niu
Chin. Phys. Lett. 2017, 34 (7): 074202 .   DOI: 10.1088/0256-307X/34/7/074202
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A four-wavelength Bragg reflection waveguide edge emitting diode based on intracavity spontaneous parametric down-conversion and four-wave mixing (FWM) processes is made. The structure and its tuning characteristic are designed by the aid of FDTD mode solution. The laser structure is grown by molecular beam epitaxy and processed to laser diode through the semiconductor manufacturing technology. Fourier transform infrared spectroscopy is applied to record wavelength information. Pump around 1.071 μm, signal around 1.77 μm, idler around 2.71 μm and FWM signal around 1.35 μm are observed at an injection current of 560 mA. The influences of temperature, carrier density and pump wavelength on tuning characteristic are shown numerically and experimentally.
Frequency Stabilization of a Microsecond Pulse Sodium Guide Star Laser with a Tilt- and Temperature-Tuned Etalon
Chang Xu, Jun-Wei Zuo, Qi Bian, Chuan Guo, Yong Bo, Lu Feng, Kai Jin, Kai Wei, Hong-Wei Gao, Sheng Zhang, Yuan-Qin Xia, Qin-Jun Peng, Zu-Yan Xu
Chin. Phys. Lett. 2017, 34 (7): 074203 .   DOI: 10.1088/0256-307X/34/7/074203
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A frequency stabilization approach is introduced for the microsecond pulse sodium beacon laser using an intra-cavity tilt- and temperature-tuned etalon based on a computer-controlled feedback system connected with a fast high-precision wavelength meter. The frequency stability of the sodium beacon lasers is compared with and without feedback loop controlling. The output wavelength of the laser is locked to the sodium D$_{2a}$ absorption line (589.159 nm) over 12 h with the feedback loop controlling technology. As a result, the sodium laser guide star is successfully observed by the telescope of National Astronomical Observatories at Xinglong. This approach can also be used for other pulses and continuous-wave lasers for the frequency stabilization.
High-Efficiency Generation of 0.12mJ, 8.6Fs Pulses at 400nm Based on Spectral Broadening in Solid Thin Plates
Yang-Yang Liu, Kun Zhao, Peng He, Hang-Dong Huang, Hao Teng, Zhi-Yi Wei
Chin. Phys. Lett. 2017, 34 (7): 074204 .   DOI: 10.1088/0256-307X/34/7/074204
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We demonstrate efficient generation of continuous spectrum centered at 400 nm from solid thin plates. By frequency doubling of 0.8 mJ, 30 fs Ti:sapphire laser pulses with a BBO crystal, 0.2 mJ, 33 fs laser pulses at 400 nm are generated. Focusing the 400-nm pulses into 7 thin fused silica plates, we obtain 0.15 mJ continuous spectrum covering 350–450 nm. After compressing by 3 pairs of chirped mirrors, 0.12 mJ, 8.6 fs pulses are achieved. To the best of our knowledge, this is the first time that sub-10-fs pulses centered at 400 nm are generated by solid thin plates, which shows that spectral broadening in solid-state materials works not only at 800 nm but also at different wavelengths.
High Coupling Efficiency of the Fiber-Coupled Module Based on Photonic-Band-Crystal Laser Diodes
Yang Chen, Yu-Fei Wang, Hong-Wei Qu, Yu-Fang Zhang, Yun Liu, Xiao-Long Ma, Xiao-Jie Guo, Peng-Chao Zhao, Wan-Hua Zheng
Chin. Phys. Lett. 2017, 34 (7): 074205 .   DOI: 10.1088/0256-307X/34/7/074205
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The coupling efficiency of the beam combination and the fiber-coupled module is limited due to the large vertical divergent angle of conventional semiconductor laser diodes. We present a high coupling efficiency module using photonic-band-crystal (PBC) laser diodes with narrow vertical divergent angles. Three PBC single-emitter laser diodes are combined into a fiber with core diameter of 105 μm and numerical aperture of 0.22. A high coupling efficiency of 94.4% is achieved and the brightness is calculated to be 1.7 MW/(cm$^{2}\cdot$sr) with the injection current of 8 A.
Effect of Phase Modulation on Electromagnetically Induced Grating in a Five-Level M-Type Atomic System
Li Wang, Yi-Hong Qi, Li Deng , Yue-Ping Niu, Shang-Qing Gong, Hong-Ju Guo
Chin. Phys. Lett. 2017, 34 (7): 074206 .   DOI: 10.1088/0256-307X/34/7/074206
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We theoretically investigate the phenomena of electromagnetically induced grating in an M-type five-level atomic system. It is found that a weak field can be effectively diffracted into high-order directions using a standing wave coupling field, and different depths of the phase modulation can disperse the diffraction light into different orders. When the phase modulation depth is approximated to the orders of $\pi$, $2\pi$ and $3\pi$, the first-, second- and third-order diffraction intensity reach the maximum, respectively. Thus we can take advantage of the phase modulation to control the probe light dispersing into the required high orders.
Generation of 47fs Pulses from an Er:Fiber Amplifier
Shang- Ming Ou, Guan-Yu Liu, Hui Lei, Zhi-Gang Zhang, Qing-Mao Zhang
Chin. Phys. Lett. 2017, 34 (7): 074207 .   DOI: 10.1088/0256-307X/34/7/074207
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We demonstrate a self-starting erbium fiber oscillator-amplifier system based on the nonlinear polarization rotation mode-locked mechanism. The direct output pulse from the amplifier is 47 fs with an average power of 1.22 W and a repetition rate of 50 MHz, corresponding to a pulse energy of 24 nJ. The full width at half-maximum of the spectrum of the output pulses is approximately 93 nm at a central wavelength of 1572 nm so that the transform-limited pulse duration is as short as 39 fs. Due to the imperfect dispersion compensation, we compress the pulses to 47 fs in this experiment.
A 526mJ Subnanosecond Pulsed Hybrid-Pumped Nd:YAG Laser
Jiang-Peng Shi, Jian-Guo Xin, Jun Liu, Jia-Bin Chen, Sher Zaman
Chin. Phys. Lett. 2017, 34 (7): 074208 .   DOI: 10.1088/0256-307X/34/7/074208
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A hybrid-pumped Nd:YAG pulse laser with a double-pass two-rod configuration is presented. The focal length of offset lens is particularly studied to compensate for the thermal lens effect and depolarization. For input pulse energy of 141 $\mu$J with pulse duration of 754 ps, the pulse laser system delivers 526 mJ pulse energy and 728 ps pulse width output at 10 Hz with pulse profile shape preservation. The energy stability of the laser pulse is less than 3%, and the beam quality factor $M^2$ is less than 2.26.
Tight Focusing Properties of Azimuthally Polarized Pair of Vortex Beams through a Dielectric Interface
C. A. P. Janet, M. Lavanya, K. B. Rajesh, M. Udhayakumar, Z. Jaroszewicz, D. Velauthapillai
Chin. Phys. Lett. 2017, 34 (7): 074209 .   DOI: 10.1088/0256-307X/34/7/074209
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Tight focusing properties of an azimuthally polarized Gaussian beam with a pair of vortices through a dielectric interface is theoretically investigated by vector diffraction theory. For the incident beam with a pair of vortices of opposite topological charges, the vortices move toward each other, annihilate and revive in the vicinity of focal plane, which results in the generation of many novel focal patterns. The usable focal structures generated through the tight focusing of the double-vortex beams may find applications in micro-particle trapping, manipulation, and material processing, etc.
Enhanced Luminescence of InGaN-Based 395nm Flip-Chip Near-Ultraviolet Light-Emitting Diodes with Al as N-Electrode
Jin Xu, Wei Zhang, Meng Peng, Jiang-Nan Dai, Chang-Qing Chen
Chin. Phys. Lett. 2017, 34 (7): 074210 .   DOI: 10.1088/0256-307X/34/7/074210
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High-reflectivity Al-based n-electrode is used to enhance the luminescence properties of InGaN-based 395 nm flip-chip near-ultraviolet (UV) light-emitting diodes. The Al-only metal layer could form the Ohmic contact on the plasma etched n-GaN by means of chemical pre-treatment, with the lowest specific contact resistance of $2.211\times10^{-5}$ $\Omega\cdot$cm$^{2}$. The Al n-electrodes enhance light output power of the 395 nm flip-chip near-UV light-emitting diodes by more than 33% compared with the Ti/Al n-electrodes. Meanwhile, the electrical characteristics of these chips with two types of n-electrodes do not show any significant discrepancy. The near-field light distribution measurement of packaged chips confirms that the enhanced luminescence is ascribed to the high reflectivity of the Al electrodes in the UV region. After the accelerated aging test for over 1000 h, the luminous degradation of the packaged chips with Al n-electrodes is less than 3%, which proves the reliability of these chips with the Al-based electrodes. Our approach shows a simplified design and fabrication of high-reflectivity n-electrode for flip-chip near-UV light emitting diodes.
A 420nm Blue Diode Laser for the Potential Rubidium Optical Frequency Standard
Sheng-Nan Zhang, Xiao-Gang Zhang, Jian-Hui Tu, Zhao-Jie Jiang, Hao-Sen Shang, Chuan-Wen Zhu, Wei Yang, Jing-Zhong Cui, Jing-Biao Chen
Chin. Phys. Lett. 2017, 34 (7): 074211 .   DOI: 10.1088/0256-307X/34/7/074211
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We report a 420 nm external cavity diode laser with an interference filter (IF) of 0.5 nm narrow-bandwidth and 79% high transmission, which is first used for Rb optical frequency standard. The IF and the cat-eye reflector are used for selecting wavelength and light feedback, respectively. The measured laser linewidth is 24 kHz when the diode laser is free running. Using this narrow-linewidth IF blue diode laser, we realize a compact Rb optical frequency standard without a complicated PDH system. The preliminary stability of the Rb optical frequency standard is $2\times10^{-13}$ at 1 s and decreases to $1.9\times10^{-14}$ at 1000 s. The narrow-linewidth characteristic makes the IF blue diode laser a well suited candidate for the compact Rb optical frequency standard.
Source Range Estimation Based on Pulse Waveform Matching in a Slope Environment
Zu-Yong Wu, Ren-He Zhang, Ji-Xing Qin, Zhao-Hui Peng, Zhou Meng
Chin. Phys. Lett. 2017, 34 (7): 074301 .   DOI: 10.1088/0256-307X/34/7/074301
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An approach of source range estimation in an ocean environment with sloping bottom is presented. The approach is based on pulse waveform correlation matching between the received and simulated signals. An acoustic propagation experiment is carried out in a slope environment. The pulse signal is received by the vertical line array, and the depth structure can be obtained. For the experimental data, the depth structures of pulse waveforms are different, which depends on the source range. For a source with unknown range, the depth structure of pulse waveform can be first obtained from the experimental data. Next, the depth structures of pulse waveforms in different ranges are numerically calculated. After the process of correlating the experimental and simulated signals, the range corresponding to the maximum value of the correlation coefficient is the estimated source range. For the explosive sources in the experiment with two depths, the mean relative errors of range estimation are both less than 7%.
Coupled Perturbed Modes over Sloping Penetrable Bottom
Fei-Long Zhu, Eric I. Thorsos, Feng-Hua Li
Chin. Phys. Lett. 2017, 34 (7): 074302 .   DOI: 10.1088/0256-307X/34/7/074302
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In environments with water depth variations, one-way modal solutions involve mode coupling. Higham and Tindle developed an accurate and fast approach using perturbation theory to locally determine the change in mode functions at steps.  The method of Higham and Tindle is limited to low frequency ($\le$250 Hz). We extend the coupled perturbation method, thus it can be applied to higher frequencies. The approach is described and some examples are given.
Simulation of Double-Front Detonation of Suspended Mixed Cyclotrimethylenetrinitramine and Aluminum Dust in Air
Wen-Tao Zan, He-Fei Dong, Tao Hong
Chin. Phys. Lett. 2017, 34 (7): 074701 .   DOI: 10.1088/0256-307X/34/7/074701
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The two-phase detonation of suspended mixed cyclotrimethylenetrinitramine (i.e., RDX) and aluminum dust in air is simulated with a two-phase flow model. The parameters of the mixed RDX-Al dust detonation wave are obtained. The double-front detonation and steady state of detonation wave of the mixed dust are analyzed. For the dust mixed RDX with density of 0.565 kg/m$^{3}$ and radius of 10 μm as well as aluminum with density of 0.145 kg/m$^{3}$ and radius of 4 μm, the detonation wave will reach a steady state at 23 m. The effects of the size of aluminum on the detonation are analyzed. For constant radius of RDX particles with radius of 10 μm, as the radius of aluminum particles is larger than 2.0 μm, the double-front detonation can be observed due to the different ignition distances and reaction rates of RDX and aluminum particles. As the radius of aluminum particles is larger, the velocity, pressure and temperature of detonation wave will be slower. The pressure at the Chapman–Jouguet (CJ) point also becomes lower. Comparing the detonation with single RDX dust, the pressure and temperature in the flow field of detonation of mixed dust are higher.
Natural Frequency of Oscillating Gaseous Bubbles in Ventilated Cavitation
Yu-Ning Zhang
Chin. Phys. Lett. 2017, 34 (7): 074702 .   DOI: 10.1088/0256-307X/34/7/074702
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An improved formula is proposed for the prediction of natural frequency of oscillating gaseous bubbles in the ventilated cavitation by considering the liquid compressibility and the thermal effects. The differences between the previous formula and ours are quantitatively discussed in terms of both dimensional parameters (e.g., frequency and bubble radius) and non-dimensional parameters (e.g., the Péclet number). Our analysis reveals that our formula is superior to the existing formula in the low-frequency excitation regions.
Oscillatory and Chaotic Buoyant-Thermocapillary Convection in the Large-Scale Liquid Bridge
Jia Wang, Li Duan, Qi Kang
Chin. Phys. Lett. 2017, 34 (7): 074703 .   DOI: 10.1088/0256-307X/34/7/074703
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To cooperate with Chinese TG-2 space experiment project, the transition process from steady to regular oscillatory flow, and finally to chaos is experimentally studied in buoyant-thermocapillary convection. The onset of oscillation and further transitional convective behavior are detected by measuring the temperature in large-scale liquid bridge of 2cSt silicone oil. To identify the various dynamical regimes, the Fourier transform and fractal theory are used to reveal the frequency and amplitude characteristics of the flow motion. The experimental results indicate the co-existence of quasi-periodic and the Feigenbaum bifurcation in chaos.
Jeans Gravitational Instability with $\kappa $-Deformed Kaniadakis Distribution
Hui Chen, Shi-Xuan Zhang, San-Qiu Liu
Chin. Phys. Lett. 2017, 34 (7): 075101 .   DOI: 10.1088/0256-307X/34/7/075101
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The Jeans instabilities in an unmagnetized, collisionless, isotropic self-gravitating matter system are investigated in the context of $\kappa$-deformed Kaniadakis distribution based on kinetic theory. The result shows that both the growth rates and critical wave numbers of Jeans instability are lower in the $\kappa$-deformed Kaniadakis distributed self-gravitating matter systems than the Maxwellian case. The standard Jeans instability for a Maxwellian case is recovered under the limitation $\kappa=0$.
Linear Growth of Rayleigh–Taylor Instability of Two Finite-Thickness Fluid Layers
Hong-Yu Guo, Li-Feng Wang, Wen-Hua Ye, Jun-Feng Wu, Wei-Yan Zhang
Chin. Phys. Lett. 2017, 34 (7): 075201 .   DOI: 10.1088/0256-307X/34/7/075201
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The linear growth of Rayleigh–Taylor instability (RTI) of two superimposed finite-thickness fluids in a gravitational field is investigated analytically. Coupling evolution equations for perturbation on the upper, middle and lower interfaces of the two stratified fluids are derived. The growth rate of the RTI and the evolution of the amplitudes of perturbation on the three interfaces are obtained by solving the coupling equations. It is found that the finite-thickness fluids reduce the growth rate of perturbation on the middle interface. However, the finite-thickness effect plays an important role in perturbation growth even for the thin layers which will cause more severe RTI growth. Finally, the dependence of the interface position under different initial conditions are discussed in some detail.
Forming of Space Charge Wave with Broad Frequency Spectrum in Helical Relativistic Two-Stream Electron Beams
A. Lysenko, I. Volk, A. Serozhko, O. Rybalko
Chin. Phys. Lett. 2017, 34 (7): 075202 .   DOI: 10.1088/0256-307X/34/7/075202
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We elaborate a quadratic nonlinear theory of plural interactions of growing space charge wave (SCW) harmonics during the development of the two-stream instability in helical relativistic electron beams. It is found that in helical two-stream electron beams the growth rate of the two-stream instability increases with the beam entrance angle. An SCW with the broad frequency spectrum, in which higher harmonics have higher amplitudes, forms when the frequency of the first SCW harmonic is much less than the critical frequency of the two-stream instability. For helical electron beams the spectrum expands with the increase of the beam entrance angle. Moreover, we obtain that utilizing helical electron beams in multiharmonic two-stream superheterodyne free-electron lasers leads to the improvement of their amplification characteristics, the frequency spectrum broadening in multiharmonic signal generation mode, and the reduction of the overall system dimensions.
Effect of Particle Number Density on Wave Dispersion in a Two-Dimensional Yukawa System
Rang-Yue Zhang, Yan-Hong Liu, Feng Huang, Zhao-Yang Chen, Chun-Yan Li
Chin. Phys. Lett. 2017, 34 (7): 075203 .   DOI: 10.1088/0256-307X/34/7/075203
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Effect of the particle number density on the dispersion properties of longitudinal and transverse lattice waves in a two-dimensional Yukawa charged-dust system is investigated using molecular dynamics simulation. The dispersion relations for the waves are obtained. It is found that the frequencies of both the longitudinal and transverse dust waves increase with the density and when the density is sufficiently high a cutoff region appears at the short wavelength. With the increase of the particle number density, the common frequency tends to increase, and the sound speed of the longitudinal wave also increases, but that of the transverse wave remains low.
Recrystallization Phase in He-Implanted 6H-SiC
Yu-Zhu Liu, Bing-Sheng Li, Hua Lin, Li Zhang
Chin. Phys. Lett. 2017, 34 (7): 076101 .   DOI: 10.1088/0256-307X/34/7/076101
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The evolution of the recrystallization phase in amorphous 6H-SiC formed by He implantation followed by thermal annealing is investigated. Microstructures of recrystallized layers in 15 keV He$^{+}$ ion implanted 6H-SiC (0001) wafers are characterized by means of cross-sectional transmission electron microscopy (XTEM) and high-resolution TEM. Epitaxial recrystallization of buried amorphous layers is observed at an annealing temperature of 900$^{\circ}\!$C. The recrystallization region contains a 3C-SiC structure and a 6H-SiC structure with different crystalline orientations. A high density of lattice defects is observed at the interface of different phases and in the periphery of He bubbles. With increasing annealing to 1000$^{\circ}\!$C, 3C-SiC and columnar epitaxial growth 6H-SiC become unstable, instead of [0001] orientated 6H-SiC. In addition, the density of lattice defects increases slightly with increasing annealing. The possible mechanisms for explanation are also discussed.
Anisotropic Migration of Defects under Strain Effect in BCC Iron
Ning Gao, Fei Gao, Zhi-Guang Wang
Chin. Phys. Lett. 2017, 34 (7): 076102 .   DOI: 10.1088/0256-307X/34/7/076102
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The basic properties of defects (self-interstitial and vacancy) in BCC iron under uniaxial tensile strain are investigated with atomic simulation methods. The formation and migration energies of them show different dependences on the directions of uniaxial tensile strain in two different computation boxes. In box-1, the uniaxial tensile strain along the $\langle 100\rangle$ direction influences the formation and migration energies of the $\langle 110 \rangle$ dumbbell but slightly affects the migration energy of a single vacancy. In box-2, the uniaxial tensile strain along the $\langle 111\rangle$ direction influences the formation and migration energies of both vacancy and interstitials. Especially, a $\langle 110 \rangle$ dumbbell has a lower migration energy when its migration direction is the same or close to the strain direction, while along these directions, a vacancy has a higher migration energy. All these results indicate that the uniaxial tensile strain can result in the anisotropic formation and migration energies of simple defects in materials.
Magnetic and Electronic Properties of Double Perovskite Ba$_{2}$SmNbO$_{6 }$ without Octahedral Tilting by First Principle Calculations
Abdelkader Khouidmi, Hadj Baltache, Ali Zaoui
Chin. Phys. Lett. 2017, 34 (7): 076103 .   DOI: 10.1088/0256-307X/34/7/076103
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The structural, magnetic and electronic properties of the double perovskite Ba$_{2}$SmNbO$_{6}$ (for the simple cubic structure where no octahedral tilting exists anymore) are studied using the density functional theory within the generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction. The total energy, the spin magnetic moment, the band structure and the density of states are calculated. The optimization of the lattice constants is 8.5173 Å, which is in good agreement with the experimental value 8.5180 Å. The calculations reveal that Ba$_{2}$SmNbO$_{6}$ has a stable ferromagnetic ground state and the spin magnetic moment per molecule is 5.00 $\mu$B/f.u. which comes mostly from the Sm$^{3+}$ ion only. By analysis of the band structure, the compound exhibits the direct band gap material and half-metallic ferromagnetic nature with 100% spin-up polarization, which implies potential applications of this new lanthanide compound in magneto-electronic and spintronic devices.
An Increase in TDDB Lifetime of Partially Depleted SOI Devices Induced by Proton Irradiation
Teng Ma, Qi-Wen Zheng, Jiang-Wei Cui, Hang Zhou, Dan-Dan Su, Xue-Feng Yu, Qi Guo
Chin. Phys. Lett. 2017, 34 (7): 076104 .   DOI: 10.1088/0256-307X/34/7/076104
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The effects of proton irradiation on the subsequent time-dependent dielectric breakdown (TDDB) of partially depleted SOI devices are experimentally investigated. It is demonstrated that heavy-ion irradiation will induce the decrease of TDDB lifetime for many device types, but we are amazed to find a measurable increase in the TDDB lifetime and a slight decrease in the radiation-induced leakage current after proton irradiation at the nominal operating irradiation bias. We interpret these results and mechanisms in terms of the effects of radiation-induced traps on the stressing current during the reliability testing, which may be significant to expand the understanding of the radiation effects of the devices used in the proton radiation environment.
Growth and Characterization of InSb Thin Films on GaAs (001) without Any Buffer Layers by MBE
Xiao-Meng Zhao, Yang Zhang, Li-Jie Cui, Min Guan, Bao-Qiang Wang, Zhan-Ping Zhu, Yi-Ping Zeng
Chin. Phys. Lett. 2017, 34 (7): 076105 .   DOI: 10.1088/0256-307X/34/7/076105
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We report the growth of InSb layers directly on GaAs (001) substrates without any buffer layers by molecular beam epitaxy (MBE). Influences of growth temperature and V/III flux ratios on the crystal quality, the surface morphology and the electrical properties of InSb thin films are investigated. The InSb samples with room-temperature mobility of 44600 cm$^{2}$/Vs are grown under optimized growth conditions. The effect of defects in InSb epitaxial on the electrical properties is researched, and we infer that the formation of In vacancy (V$_{\rm In})$ and Sb anti-site (Sb$_{\rm In})$ defects is the main reason for concentrations changing with growth temperature and Sb$_{2}$/In flux ratios. The mobility of the InSb sample as a function of temperature ranging from 90 K to 360 K is demonstrated and the dislocation scattering mechanism and phonon scattering mechanism are discussed.
Temperature-Dependent Photoluminescence Analysis of 1.0MeV Electron Irradiation-Induced Nonradiative Recombination Centers in n$^{+}$–p GaAs Middle Cell of GaInP/GaAs/Ge Triple-Junction Solar Cells
Jun-Ling Wang, Tian-Cheng Yi, Yong Zheng, Rui Wu, Rong Wang
Chin. Phys. Lett. 2017, 34 (7): 076106 .   DOI: 10.1088/0256-307X/34/7/076106
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The effects of irradiation of 1.0 MeV electrons on the n$^{+}$–p GaAs middle cell of GaInP/GaAs/Ge triple-junction solar cells are investigated by temperature-dependent photoluminescence (PL) measurements in the 10–300 K temperature range. The appearance of thermal quenching of the PL intensity with increasing temperature confirms the presence of a nonradiative recombination center in the cell after the electron irradiation, and the thermal activation energy of the center is determined using the Arrhenius plot of the PL intensity. Furthermore, by comparing the thermal activation and the ionization energies of the defects, the nonradiative recombination center in the n$^{+}$–p GaAs middle cell acting as a primary defect is identified as the E5 electron trap located at $E_{\rm c}-0.96$ eV.
LaB$_{6}$ Work Function and Structural Stability under High Pressure
Peng-Shan Li, Wei-Ran Cui, Rui Li, Hua-Lei Sun, Yan-Chun Li, Dong-Liang Yang, Yu Gong, Hui Li, Xiao-Dong Li
Chin. Phys. Lett. 2017, 34 (7): 076201 .   DOI: 10.1088/0256-307X/34/7/076201
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The work functions of the (110) and (100) surfaces of LaB$_{6}$ are determined from ambient pressure to 39.1 GPa. The work function of the (110) surface slowly decreases but that of the (100) surface remains at a relatively constant value. To determine the reason for this difference, the electron density distribution (EDD) is determined from high-pressure single-crystal x-ray diffraction data by the maximum entropy method. The EDD results show that the chemical bond properties in LaB$_{6}$ play a key role. The structural stability of LaB$_{6}$ under high pressure is also investigated by single-crystal x-ray diffraction. In this study, no structural or electronic phase transition is observed from ambient pressure to 39.1 GPa.
An Analysis of Structural-Acoustic Coupling Band Gaps in a Fluid-Filled Periodic Pipe
Dian-Long Yu, Chun-Yang Du, Hui-Jie Shen, Jiang-Wei Liu, Ji-Hong Wen
Chin. Phys. Lett. 2017, 34 (7): 076202 .   DOI: 10.1088/0256-307X/34/7/076202
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A periodic pipe system composed of steel pipes and rubber hoses with the same inner radius is designed based on the theory of phononic crystals. Using the transfer matrix method, the band structure of the periodic pipe is calculated considering the structural-acoustic coupling. The results show that longitudinal vibration band gaps and acoustic band gaps can coexist in the fluid-filled periodic pipe. The formation of the band gap mechanism is further analyzed. The band gaps are validated by the sound transmission loss and vibration-frequency response functions calculated using the finite element method. The effect of the damp on the band gap is analyzed by calculating the complex band structure. The periodic pipe system can be used not only in the field of vibration reduction but also for noise elimination.
Coupled Two-Dimensional Atomic Oscillation in an Anharmonic Trap
Dong Hu, Lin-Xiao Niu, Jia-Hua Zhang, Xin-Hao Zou, Shu-Yang Cao, Xiao-Ji Zhou
Chin. Phys. Lett. 2017, 34 (7): 076701 .   DOI: 10.1088/0256-307X/34/7/076701
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In atomic dynamics, oscillation along different axes can be studied separately in the harmonic trap. When the trap is not harmonic, motion in different directions may couple together. In this work, we observe a two-dimensional oscillation by exciting atoms in one direction, where the atoms are transferred to an anharmonic region. Theoretical calculations are coincident to the experimental results. These oscillations in two dimensions not only can be used to measure trap parameters but also have potential applications in atomic interferometry and precise measurements.
Topological Nodal Line Semimetal in Non-Centrosymmetric PbTaS$_2$
Jian-Peng Sun
Chin. Phys. Lett. 2017, 34 (7): 077101 .   DOI: 10.1088/0256-307X/34/7/077101
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Topological semimetals are a new type of matter with one-dimensional Fermi lines or zero-dimensional Weyl or Dirac points in momentum space. Here using first-principles calculations, we find that the non-centrosymmetric PbTaS$_2$ is a topological nodal line semimetal. In the absence of spin-orbit coupling (SOC), one band inversion happens around a high symmetrical $H$ point, which leads to forming a nodal line. The nodal line is robust and protected against gap opening by mirror reflection symmetry even with the inclusion of strong SOC. In addition, it also hosts exotic drumhead surface states either inside or outside the projected nodal ring depending on surface termination. The robust bulk nodal lines and drumhead-like surface states with SOC in PbTaS$_2$ make it a potential candidate material for exploring the freakish properties of the topological nodal line fermions in condensed matter systems.
Analytic Continuation with Padé Decomposition
Xing-Jie Han, Hai-Jun Liao, Hai-Dong Xie, Rui-Zhen Huang, Zi-Yang Meng, Tao Xiang
Chin. Phys. Lett. 2017, 34 (7): 077102 .   DOI: 10.1088/0256-307X/34/7/077102
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The ill-posed analytic continuation problem for Green's functions or self-energies can be carried out using the Padé rational polynomial approximation. However, to extract accurate results from this approximation, high precision input data of the Matsubara Green function are needed. The calculation of the Matsubara Green function generally involves a Matsubara frequency summation, which cannot be evaluated analytically. Numerical summation is requisite but it converges slowly with the increase of the Matsubara frequency. Here we show that this slow convergence problem can be significantly improved by utilizing the Padé decomposition approach to replace the Matsubara frequency summation by a Padé frequency summation, and high precision input data can be obtained to successfully perform the Padé analytic continuation.
Boundary Hamiltonian Theory for Gapped Topological Orders
Yuting Hu, Yidun Wan, Yong-Shi Wu
Chin. Phys. Lett. 2017, 34 (7): 077103 .   DOI: 10.1088/0256-307X/34/7/077103
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We report our systematic construction of the lattice Hamiltonian model of topological orders on open surfaces, with explicit boundary terms. We do this mainly for the Levin-Wen string-net model. The full Hamiltonian in our approach yields a topologically protected, gapped energy spectrum, with the corresponding wave functions robust under topology-preserving transformations of the lattice of the system. We explicitly present the wavefunctions of the ground states and boundary elementary excitations. The creation and hopping operators of boundary quasi-particles are constructed. It is found that given a bulk topological order, the gapped boundary conditions are classified by Frobenius algebras in its input data. Emergent topological properties of the ground states and boundary excitations are characterized by (bi-) modules over Frobenius algebras.
Modelling Magnetoresistance Effect in Limited Anisotropic Semiconductors
Filippov V. V., Mitsuk S.V.
Chin. Phys. Lett. 2017, 34 (7): 077201 .   DOI: 10.1088/0256-307X/34/7/077201
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A macroscopic model of the magnetoresistance effect in limited anisotropic semiconductors is built. This model allows us to solve the problem of measurement of physical magnetoresistance components of crystals and films. Based on a unified mathematical model the method is worked out enabling us to measure tensor components of the specific electrical resistance and the relative magnetoresistance of anisotropic semiconductors simultaneously.
Spin Noise Spectroscopy in N-GaAs: Spin Relaxation of Localized Electrons
Jian Ma, Ping Shi, Xuan Qian, Ya-Xuan Shang, Yang Ji
Chin. Phys. Lett. 2017, 34 (7): 077202 .   DOI: 10.1088/0256-307X/34/7/077202
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Spin noise spectroscopy (SNS) of electrons in n-doped bulk GaAs is studied as functions of temperature and the probe-laser energy. Experimental results show that the SNS signal comes from localized electrons in the donor band. The spin relaxation time of electrons, which is retrieved from the SNS measurement, depends on the probe light energy and temperature, and it can be ascribed to the variation of electron localization degree.
BiPh-$m$-BiDPO as a Hole-Blocking Layer for Organic Light-Emitting Diodes: Revealing Molecular Structure-Properties Relationship
Ning-Ning Chen, Wan-Yi Tan, Dong-Yu Gao, Jian-Hua Zou, Jun-Zhe Liu, Jun-Biao Peng, Yong Cao, Xu-Hui Zhu
Chin. Phys. Lett. 2017, 34 (7): 077203 .   DOI: 10.1088/0256-307X/34/7/077203
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We report a simple hole-blocking material (biphenyl-3,3'-diyl)bis(diphenylphosphine oxide) (BiPh-$m$-BiDPO) based on our recent advance. The bis(phosphine oxide) compound shows HOMO/LUMO levels of $\sim$$-6.71/-2.51$ eV. Its phosphorescent spectrum in a solid film features two major emission bands peaking at 2.69 and 2.4 eV, corresponding to 0–0 and 0–1 vibronic transitions, respectively. The measurement of the electron-only devices reveals that BiPh-$m$-BiDPO possesses electron mobility of $2.28\times10^{-9}$–$3.22\times10^{-8}$ cm$^{2}$V$^{-1}$s$^{-1}$ at $E=2$–$5\times10^{5}$ V/cm. The characterization of the sky blue fluorescent and red phosphorescent pin organic light-emitting diodes (OLEDs) utilizing BiPh-$m$-BiDPO as the hole blocker shows that its shallow LUMO level as well as the low electron mobility affects significantly the power efficiency and hence operational stability, relative to the luminous efficiency, especially at high luminance. In combination with our recent results, the present study provides an indepth insight on the molecular structure-property correlation in the organic phosphinyl-containing hole-blocking materials.
The Efficiency Droop of InGaN-Based Green LEDs with Different Superlattice Growth Temperatures on Si Substrates via Temperature-Dependent Electroluminescence
Wei-Jing Qi, Long-Quan Xu, Chun-Lan Mo, Xiao-Lan Wang, Jie Ding, Guang-Xu Wang, Shuan Pan, Jian-Li Zhang, Xiao-Ming Wu, Jun-Lin Liu, Feng-Yi Jiang
Chin. Phys. Lett. 2017, 34 (7): 077301 .   DOI: 10.1088/0256-307X/34/7/077301
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InGaN-based green light-emitting diodes (LEDs) with different growth temperatures of superlattice grown on Si (111) substrates are investigated by temperature-dependent electroluminescence between 100 K and 350 K. It is observed that with the decrease of the growth temperature of the superlattice from 895$^{\circ}\!$C to 855$^{\circ}\!$C, the forward voltage decreases, especially at low temperature. We presume that this is due to the existence of the larger average size of V-shaped pits, which is determined by secondary ion mass spectrometer measurements. Meanwhile, the sample with higher growth temperature of superlattice shows a severer efficiency droop at cryogenic temperatures (about 100 K–150 K). Electron overflow into p-GaN is considered to be the cause of such phenomena, which is relevant to the poorer hole injection into multiple quantum wells and the more reduced effective active volume in the active region.
Revisiting the Electron-Doped SmFeAsO: Enhanced Superconductivity up to 58.6K by Th and F Codoping
Xiao-Chuan Wang, Jia Yu, Bin-Bin Ruan, Bo-Jin Pan, Qing-Ge Mu, Tong Liu, Kang Zhao, Gen-Fu Chen, Zhi-An Ren
Chin. Phys. Lett. 2017, 34 (7): 077401 .   DOI: 10.1088/0256-307X/34/7/077401
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In the iron-based high-$T_{\rm c}$ bulk superconductors, $T_{\rm c}$ above 50 K was only observed in the electron-doped 1111-type compounds. Here we revisit the electron-doped SmFeAsO polycrystals to make a further investigation for the highest $T_{\rm c}$ in these materials. To introduce more electron carriers and less crystal lattice distortions, we study the Th and F codoping effects into the Sm-O layers with heavy electron doping. Dozens of Sm$_{1-x}$Th$_{x}$FeAsO$_{1-y}$F$_{y}$ samples are synthesized through the solid state reaction method, and these samples are carefully characterized by the structural, resistive, and magnetic measurements. We find that the codoping of Th and F clearly enhances the superconducting $T_{\rm c}$ more than the Th or F single-doped samples, with the highest record $T_{\rm c}$ up to 58.6 K when $x=0.2$ and $y=0.225$. Further element doping causes more impurities and lattice distortions in the samples with a weakened superconductivity.
In Situ Electronic Structure Study of Epitaxial Niobium Thin Films by Angle-Resolved Photoemission Spectroscopy
Pai Xiang, Ji-Shan Liu, Ming-Ying Li, Hai-Feng Yang, Zheng-Tai Liu, Cong-Cong Fan, Da-Wei Shen , Zhen Wang, Zhi Liu
Chin. Phys. Lett. 2017, 34 (7): 077402 .   DOI: 10.1088/0256-307X/34/7/077402
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High-quality single crystalline niobium films are grown on a-plane sapphire in molecular beam epitaxy. The film is single crystalline with a (110) orientation, and both the rocking curve and the reflection high-energy electron diffraction pattern demonstrate its high-quality with an atomically smooth surface. By in situ study of its electronic structure, a rather weak electron-electron correlation effect is demonstrated experimentally in this $4d$ transition metal. Moreover, a kink structure is observed in the electronic structure, which may result from electron-phonon interaction and it might contribute to the superconductivity. Our results help to understand the properties of niobium deeply.
Proximity-Induced Superconductivity in New Superstructures on 2H-NbSe$_2$ Surface
Xing-Yuan Hou, Ya-Dong Gu, Zong Wang, Hai Zi, Xiang-De Zhu, Meng-Di Zhang , Chun-Hong Li, Cong Ren, Lei Shan
Chin. Phys. Lett. 2017, 34 (7): 077403 .   DOI: 10.1088/0256-307X/34/7/077403
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Using scanning tunneling microscopy we observe a stripe phase smoothly interfacing with a triangular $2\times2$ superstructure on the surface of 2H-NbSe$_2$ single crystal. Proximity-induced superconductivity is demonstrated in these new ordered structures by measurements of low-temperature tunneling spectra. The modulation of superconductivity by the reconstruction provides an opportunity to understand the interplay between superconductivity and charge orders.
Superconducting (Li,Fe)OHFeSe Film of High Quality and High Critical Parameters
Yulong Huang, Zhongpei Feng, Shunli Ni, Jun Li, Wei Hu, Shaobo Liu, Yiyuan Mao, Huaxue Zhou, Fang Zhou, Kui Jin, Huabing Wang, Jie Yuan, Xiaoli Dong, Zhongxian Zhao
Chin. Phys. Lett. 2017, 34 (7): 077404 .   DOI: 10.1088/0256-307X/34/7/077404
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A superconducting film of (Li$_{1-x}$Fe$_{x})$OHFeSe is reported for the first time. The thin film exhibits a small in-plane crystal mosaic of 0.22$^{\circ}$, in terms of the full width at half maximum of the x-ray rocking curve, and an excellent out-of-plane orientation by x-ray $\varphi $-scan. Its bulk superconducting transition temperature $T_{\rm c}$ of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field $H_{\rm c2}$ is estimated to be 79.5 T and 443 T for the magnetic field perpendicular and parallel to the $ab$ plane, respectively. Moreover, a large critical current density $J_{\rm c}$ of a value over 0.5 MA/cm$^{2}$ is achieved at $\sim $20 K. Such a (Li$_{1-x}$Fe$_{x})$OHFeSe film is therefore not only important to the fundamental research for understanding the high-$T_{\rm c}$ mechanism, but also promising in the field of high-$T_{\rm c}$ superconductivity application, especially in high-performance electronic devices and large scientific facilities such as superconducting accelerator.
Weyl and Nodal Ring Magnons in Three-Dimensional Honeycomb Lattices
Kang-Kang Li, Jiang-Ping Hu
Chin. Phys. Lett. 2017, 34 (7): 077501 .   DOI: 10.1088/0256-307X/34/7/077501
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We study the topological properties of magnon excitations in a wide class of three-dimensional (3D) honeycomb lattices with ferromagnetic ground states. It is found that they host nodal ring magnon excitations. These rings locate on the same plane in the momentum space. The nodal ring degeneracy can be lifted by the Dzyaloshinskii–Moriya interactions to form two Weyl points with opposite charges. We explicitly discuss these physics in the simplest 3D honeycomb lattice and the hyperhoneycomb lattice, and show drumhead and arc surface states in the nodal ring and Weyl phases, respectively, due to the bulk-boundary correspondence.
Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu$_3$Zn(OH)$_6$FBr
Zili Feng, Zheng Li, Xin Meng, Wei Yi, Yuan Wei, Jun Zhang, Yan-Cheng Wang, Wei Jiang, Zheng Liu, Shiyan Li, Feng Liu, Jianlin Luo, Shiliang Li, Guo-qing Zheng, Zi Yang Meng, Jia-Wei Mei, Youguo Shi
Chin. Phys. Lett. 2017, 34 (7): 077502 .   DOI: 10.1088/0256-307X/34/7/077502
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We report a new kagome quantum spin liquid candidate Cu$_3$Zn(OH)$_6$FBr, which does not experience any phase transition down to 50 mK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature ($\sim$200 K). A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from $^{19}$F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fractionalization in the fractional quantum Hall state.
Abnormal Polarity Effects of Streamer Discharge in Propylene Carbonate under Microsecond Pulses
Hong-Wei Liu, Yan-Pan Hou, Zi-Cheng Zhang, Jian Xu
Chin. Phys. Lett. 2017, 34 (7): 077701 .   DOI: 10.1088/0256-307X/34/7/077701
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Propylene carbonate (PC) has a great potential to be used as an energy storage medium in the compact pulsed power sources due to its high dielectric constant and large resistivity. We investigate both the positive and negative breakdown characteristics of PC. The streamer patterns are obtained by ultra-high-speed cameras. The experimental results show that the positive breakdown voltage of PC is about 135% higher than the negative one, which is abnormal compared with the common liquid. The shape of the positive streamer is filamentary and branchy, while the negative streamer is tree-like and less branched. According to these experimental results, a charge layer structure model at the interface between the metal electrode and liquid is presented. It is suggested that the abnormal polarity effect basically arises from the electric field strength difference in the interface between both electrodes and PC. What is more, the recombination radiation and photoionization also play an important role in the whole discharge process.
Fluorescence Intermittency in Monolayer WSe$_{2}$
Yan-Xia Ye, Xiu-Ming Dou, Kun Ding, Fu-Hua Yang, De-Sheng Jiang, Bao-Quan Sun
Chin. Phys. Lett. 2017, 34 (7): 077801 .   DOI: 10.1088/0256-307X/34/7/077801
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Fluorescence intermittent dynamics of single quantum emitters in monolayer WSe$_{2}$ are investigated via measuring spectrally resolved time traces and time-dependent fluorescence intensity trajectories. Analysis of fluorescence trajectories and spectral shifting reveal a correlation between the fluorescence intermittency and spectral diffusion. A model of an inverse power law can be used to understand the observed blinking dynamics.
X-Ray Radiation Sensing Properties of ZnS Thin Film: A Study on the Effect of Annealing
M. P. Sarma, J. M. Kalita, G. Wary
Chin. Phys. Lett. 2017, 34 (7): 077802 .   DOI: 10.1088/0256-307X/34/7/077802
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Chemically synthesized ZnS thin film is found to be a good x-ray radiation sensor. We report the effect of annealing on the x-ray radiation detection sensitivity of a ZnS thin film synthesized by a chemical bath deposition technique. The chemically synthesized ZnS films are annealed at 333, 363 and 393 K for 1 h. Structural analyses show that the lattice defects in the films decrease with annealing. Further, the band gap is also found to decrease from 3.38 to 3.21 eV after annealing at 393 K. Current-voltage characteristics of the films are studied under dark and x-ray irradiation conditions. Due to the decrease of lattice defects and band gap, the conductivity under dark conditions is found to increase from $2.06\times10^{-6}$ to $1.69\times10^{-5}$ S/cm, while that under x-ray irradiation increases from $4.13\times10^{-5}$ to $5.28\times10^{-5}$ S/cm. On the other hand, the x-ray radiation detection sensitivity of the films is found to decrease with annealing. This decrease of detection sensitivity is attributed to the decrease of the band gap as well as some structural and surface morphological changes occurring after annealing.
Dependence of Nonlinear Optical Response of Anatase TiO$_{2}$ on Shape and Excitation Intensity
Lu-Hua Guo, Ying-Wei Wang, Yong-Qiang Jiang, Si Xiao, Jun He
Chin. Phys. Lett. 2017, 34 (7): 077803 .   DOI: 10.1088/0256-307X/34/7/077803
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Nonlinear optical (NLO) properties of anatase TiO$_{2}$ with nanostructures of nanoparticle (NP), nanowire (NW) and annealed nanowire (NWA) are studied by open-aperture and closed-aperture $Z$-scan techniques with a femtosecond pulsed laser at wavelengths of 532 nm and 780 nm simultaneously. At 532 nm, when increasing excitation intensity, NLO absorption of TiO$_{2}$ NPs transforms from saturable absorption to reverse-saturable absorption. However, NWs and NWAs exhibit the opposite change. At 780 nm, all samples show reverse-saturable absorption, but have different sensitivities to excitation intensity. Due to the larger surface-to-volume ratio of NPs and less defects of NWAs by annealing, nonlinear optical absorption coefficients follow the order NPs$\ge$NWs$\ge$NWAs. The results also show that these shape and annealing effects are dominant at low excitation intensity, but do not exhibit at the high excitation intensity. The NLO refractive index of NPs shows a positive linear relationship with the excitation intensity, whereas NW and NWAs exhibit a negative linear relationship. The results could provide some foundational guidance to applications of anatase TiO$_{2}$ in optoelectronic devices or other aspects.
Observation of Temperature Induced Plasma Frequency Shift in an Extremely Large Magnetoresistance Compound LaSb
Wen-Jing Ban, Wen-Ting Guo, Jian-Lin Luo, Nan-Lin Wang
Chin. Phys. Lett. 2017, 34 (7): 077804 .   DOI: 10.1088/0256-307X/34/7/077804
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We report an optical spectroscopy study on LaSb, a compound recently identified to exhibit extremely large magnetoresistance. Our optical measurement indicates that the material has a low carrier density. More interestingly, the study reveals that the plasma frequency increases with decreasing temperature. This phenomenon suggests either an increase of the conducting carrier density or/and a decrease of the effective mass of carriers with decreasing temperature. We attribute it primarily to the latter effect. Two possible scenarios on its physical origin are examined and discussed. The study offers new insight into the electronic structure of this compound.
Experimental $I$–$V$ and $C$–$V$ Analysis of Schottky-Barrier Metal-Oxide-Semiconductor Field Effect Transistors with Epitaxial NiSi$_{2}$ Contacts and Dopant Segregation
Yi-Ze Wang, Chang Liu, Jian-Hui Cai, Qiang Liu, Xin-Ke Liu, Wen-Jie Yu, Qing-Tai Zhao
Chin. Phys. Lett. 2017, 34 (7): 078501 .   DOI: 10.1088/0256-307X/34/7/078501
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We present an experimental analysis of Schottky-barrier metal-oxide-semiconductor field effect transistors (SB-MOSFETs) fabricated on ultrathin body silicon-on-insulator substrates with a steep junction by the dopant implantation into the silicide process. The subthreshold swing of such SB-MOSFETs reaches 69 mV/dec. Emphasis is placed on the capacitance-voltage analysis of p-type SB-MOSFETs. According to the measurements of gate-to-source capacitance $C_{\rm gs}$ with respect to $V_{\rm gs}$ at various $V_{\rm ds}$, we find that a maximum occurs at the accumulation regime due to the most imbalanced charge distribution along the channel. At each $C_{\rm gs}$ peak, the difference between $V_{\rm gs}$ and $V_{\rm ds}$ is equal to the Schottky barrier height (SBH) for NiSi$_{2}$ on highly doped silicon, which indicates that the critical condition of channel pinching off is related with SBH for source/drain on channel. The SBH for NiSi$_{2}$ on highly doped silicon can affect the pinch-off voltage and the saturation current of SB-MOSFETs.
Hetero-Epitaxy and Self-Adaptive Stressor Based on Freestanding Fin for the 10nm Node and Beyond
Guang-Xing Wan, Gui-Lei Wang, Hui-Long Zhu
Chin. Phys. Lett. 2017, 34 (7): 078502 .   DOI: 10.1088/0256-307X/34/7/078502
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A promising technology named epitaxy on nano-scale freestanding fin (ENFF) is firstly proposed for hetero-epitaxy. This technology can effectively release total strain energy and then can reduce the probability of generating mismatch dislocations. Based on the calculation, dislocation defects can be eliminated completely when the thickness of the Si freestanding fin is less than 10 nm for the epitaxial Ge layer. In addition, this proposed ENFF process can provide sufficient uniaxial stress for the epitaxy layer, which can be the major stressor for the SiGe or Ge channel fin field-effect transistor or nanowire at the 10 nm node and beyond. According to the results of technology computer-aided design simulation, nanowires integrated with ENFF show excellent electrical performance for uniaxial stress and band offset. The ENFF process is compatible with the state of the art mainstream technology, which has a good potential for future applications.
Optical Field Confinement Enhanced Single ZnO Microrod UV Photodetector
Ming Wei, Chun-Xiang Xu, Fei-Fei Qin, Arumugam Gowri Manohari, Jun-Feng Lu, Qiu-Xiang Zhu
Chin. Phys. Lett. 2017, 34 (7): 078503 .   DOI: 10.1088/0256-307X/34/7/078503
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ZnO microrods are synthesized using the vapor phase transport method, and the magnetron sputtering is used to decorate the Al nanoparticles (NPs) on a single ZnO microrod. The micro-PL and $I$–$V$ responses are measured before and after the decoration of Al NPs. The FDTD stimulation is also carried out to demonstrate the optical field distribution around the decoration of Al NPs on the surface of a ZnO microrod. Due to an implementation of Al NPs, the ZnO microrod exhibits an improved photoresponse behavior. In addition, Al NPs induced localized surface plasmons (LSPs) as well as improved optical field confinement can be ascribed to an enhancement of ultraviolet (UV) response. This research provides a method for improving the responsivity of photodetectors.
Energy Conditions and Constraints on the Generalized Non-Local Gravity Model
Ya-Bo Wu, Xue Zhang, Bo-Hai Chen, Nan Zhang, Meng-Meng Wu
Chin. Phys. Lett. 2017, 34 (7): 079801 .   DOI: 10.1088/0256-307X/34/7/079801
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We study and derive the energy conditions in generalized non-local gravity, which is the modified theory of general relativity obtained by adding a term $m^{2n-2}R\Box^{-n}R$ to the Einstein–Hilbert action. Moreover, to obtain some insight on the meaning of the energy conditions, we illustrate the evolutions of four energy conditions with the model parameter $\varepsilon$ for different $n$. By analysis we give the constraints on the model parameters $\varepsilon$.
67 articles