Volume 35 Issue 5

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Higher-Order Inhomogeneous Generalized Heisenberg Supermagnetic Model
Zhao-Wen Yan, Mei-Na Zhang Ji-Feng Cui
Chin. Phys. Lett. 2018, 35 (5): 050201 .   DOI: 10.1088/0256-307X/35/5/050201
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We construct the fourth-order inhomogeneous generalized HS model and investigate the integrability property of the supersymmetric integrable system. Moreover, in terms of the gauge transformation, we investigate the corresponding gauge equivalent counterparts under two constraints, i.e., the super inhomogeneous generalized nonlinear Schrödinger equation and the fermionic inhomogeneous generalized nonlinear Schrödinger equation.
Rogue Waves in Nonintegrable KdV-Type Systems
Senyue Lou, Ji Lin
Chin. Phys. Lett. 2018, 35 (5): 050202 .   DOI: 10.1088/0256-307X/35/5/050202
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It is proved that rogue waves can be found in Korteweg de-Vries (KdV) systems if real nonintegrable effects, higher order nonlinearity and nonlinear diffusion are considered. Rogue waves can also be formed without modulation instability which is considered as the main formation mechanism of the rogue waves.
Dynamical Evolution of an Effective Two-Level System with $\mathcal{PT}$ Symmetry
Lei Du, Zhihao Xu, Chuanhao Yin, Liping Guo
Chin. Phys. Lett. 2018, 35 (5): 050301 .   DOI: 10.1088/0256-307X/35/5/050301
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We investigate the dynamics of parity- and time-reversal ($\mathcal{PT}$) symmetric two-energy-level atoms in the presence of two optical and one radio-frequency fields. The strength and relative phase of fields can drive the system from the unbroken to the broken $\mathcal{PT}$ symmetric regions. Compared with the Hermitian model, Rabi-type oscillation is still observed, and the oscillation characteristics are also adjusted by the strength and relative phase in the region of the unbroken $\mathcal{PT}$ symmetry. At the exception point, the oscillation breaks down. To better understand the underlying properties we study the effective Bloch dynamics and find that the emergence of the $z$ components of the fixed points is the feature of the $\mathcal{PT}$ symmetry breaking and the projections in the $x$–$y$ plane can be controlled with high flexibility compared with the standard two-level system with the $\mathcal{PT}$ symmetry. It helps to study the dynamic behavior of the complex $\mathcal{PT}$ symmetric model.
Quasinormal Modes of a Noncommutative-Geometry-Inspired Schwarzschild Black Hole: Gravitational, Electromagnetic and Massless Dirac Perturbations
Jun Liang
Chin. Phys. Lett. 2018, 35 (5): 050401 .   DOI: 10.1088/0256-307X/35/5/050401
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In our previous work [Chin. Phys. Lett. 35 (2018) 010410], the quasinormal modes of massless scalar field perturbation in a noncommutative-geometry-inspired Schwarzschild black hole spacetime are studied using the third-order Wentzel–Kramers–Brillouin approximative approach. In this study, we extend the work to the cases of gravitational, electromagnetic and massless Dirac perturbations. The result further confirms that the noncommutative parameter plays an important role for the quasinormal frequencies.
Combining Cubic Spline Interpolation and Fast Fourier Transform to Extend Measuring Range of Reflectometry
Ju Cheng, Jian Lu, Hong-Chao Zhang, Feng Lei, Maryam Sardar, Xin-Tian Bian, Fen Zuo, Zhong-Hua Shen, Xiao-Wu Ni, Jin Shi
Chin. Phys. Lett. 2018, 35 (5): 050701 .   DOI: 10.1088/0256-307X/35/5/050701
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The reflectometry is a common method used to measure the thickness of thin films. Using a conventional method, its measurable range is limited due to the low resolution of the current spectrometer embedded in the reflectometer. We present a simple method, using cubic spline interpolation to resample the spectrum with a high resolution, to extend the measurable transparent film thickness. A large measuring range up to 385 μm in optical thickness is achieved with the commonly used system. The numerical calculation and experimental results demonstrate that using the FFT method combined with cubic spline interpolation resampling in reflectrometry, a simple, easy-to-operate, economic measuring system can be achieved with high measuring accuracy and replicability.
Squeezed Back-to-Back Correlation of $D^0\!{\bar D}^0$ in Relativistic Heavy-Ion Collisions
Ai-Geng Yang, Yong Zhang, Luan Cheng, Hao Sun, Wei-Ning Zhang
Chin. Phys. Lett. 2018, 35 (5): 052501 .   DOI: 10.1088/0256-307X/35/5/052501
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We investigate the squeezed back-to-back correlation (BBC) of $D^0\!{\bar D}^0$ in relativistic heavy-ion collisions, using the in-medium mass modification calculated with a self-energy in hot pion gas and the source space-time distributions provided by the viscous hydrodynamic code VISH2+1. It is found that the squeezed BBC of $D^0\!{\bar D}^0$ is significant in peripheral Au+Au collisions at the relativistic heavy ion collider energy. A possible way to detect the squeezed BBC in an experiment is presented.
Internal Features of Fiber Fuse in a Yb-Doped Double-Clad Fiber at 3kW
Qi-Rong Xiao, Jia-Ding Tian, Yu-Sheng Huang, Xue-Jiao Wang, Ze-Hui Wang, Dan Li, Ping Yan, Ma-Li Gong
Chin. Phys. Lett. 2018, 35 (5): 054201 .   DOI: 10.1088/0256-307X/35/5/054201
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We study internal features of fiber fuse in a Yb-doped double-clad fiber. The samples of fiber fuse are acquired at the power level of 3 kW in an all-fiber forward-pumped master oscillator power amplifier configuration fiber laser that is built specially for fiber fuse analyses. At this high power level, drastic refractive-index redistribution arises in an expended high refractive index area around the bullet-shaped voids of fiber fuse. Electron spin resonance analyses on post-fiber-fuse samples of the Yb-doped double-clad fiber indicate rising Frenkel defect concentration, meanwhile showing a new resonance center that is different from the ones of the Ge-doped fibers studied previously. This new resonance center probably suggests the generation of Al-oxygen hole center, a kind of defect formed during the catastrophic fuse process.
Nonreciprocal Single Photon Frequency Conversion via Chiral Coupling between a V-Type System and a Pair of Waveguides
Ce Shi, Mu-Tian Cheng, Xiao-San Ma, Dong Wang, Xianshan Huang, Bing Wang, Jia-Yan Zhang
Chin. Phys. Lett. 2018, 35 (5): 054202 .   DOI: 10.1088/0256-307X/35/5/054202
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The single photon frequency conversion is investigated theoretically in the system composed of a V-type system chiral coupling to a pair of waveguides. The single photon scattering amplitudes are obtained using the real-space Hamiltonian. The calculated results show that the probability of single photon frequency down- or up-conversion can reach a unit by choosing appropriate parameters in the non-dissipative system with perfect chiral coupling. We present a nonreciprocal single photon beam splitter whose frequency of the output photon is different from that of the input photon. The influences of dissipations and non-perfect chiral coupling on the single frequency conversion are also shown. Our results may be useful in designing quantum devices at the single-photon level.
Superpixel-Based Complex Field Modulation Using a Digital Micromirror Device for Focusing Light through Scattering Media
You-Quan Jia, Qi Feng, Bin Zhang, Wei Wang, Cheng-You Lin, Ying-Chun Ding
Chin. Phys. Lett. 2018, 35 (5): 054203 .   DOI: 10.1088/0256-307X/35/5/054203
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We present a digital micromirror device (DMD) based superpixel method for focusing light through scattering media by modulating the complex field of incident light. Firstly, we numerically and experimentally investigate focusing light through a scattering sample using the superpixel methods with different target complex fields. Then, single-point and multiple-point focusing experiments are performed using this superpixel-based complex modulation method. In our experiment, up to 71.5% relative enhancement is realized. The use of the DMD-based superpixel method for the control of the complex field of incident light opens an avenue to improve the enhancement of focusing light through scattering media.
Laser Intensity Variation in Amplitude and Phase Induced by Elliptically Polarized Feedback
Hai-Sha Niu, Lian-Qing Zhu, Jian-Jun Song
Chin. Phys. Lett. 2018, 35 (5): 054204 .   DOI: 10.1088/0256-307X/35/5/054204
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The laser output characteristics under elliptically polarized optical feedback effect are studied. Elliptically polarized light is generated by wave plate placed in the feedback cavity. By analyzing the amplitude and phase of the laser output in the orthogonal direction, some new phenomena are firstly discovered and explained theoretically. Elliptically polarized feedback light is amplified in the gain medium in the resonator, and the direction perpendicular to the original polarization direction is easiest to oscillate. The laser intensity variation in amplitude and phase are related to the amplified mode and the anisotropy of external cavity. The theoretical analysis and experimental results agree well. Because the output characteristic of the laser has a relationship with the anisotropy of the external cavity, the phenomenon also provides a method for measuring birefringence.
Widely Tunable Middle Infrared Optical Parametric Oscillator Pumped by the Q-Switched Ho:GdVO$_{4}$ Laser
Xiao-Ming Duan, Cheng Chen, Yu Ding, Bao-Quan Yao, Yue-Zhu Wang
Chin. Phys. Lett. 2018, 35 (5): 054205 .   DOI: 10.1088/0256-307X/35/5/054205
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We demonstrate a middle infrared ZnGeP$_{2}$ optical parametric oscillator pumped by the Q-switched Ho:GdVO$_{4}$ laser. When the incident Ho pump power is 4.12 W, the maximum average output power of the ZGP-OPO laser is 2.05 W, corresponding to a slope efficiency of 74.6%. The ZGP-OPO laser produces 4.2 ns mid-infrared pulses at a pulse repetition rate of 5 kHz. In addition, we obtain 0.8 μm of tunable range for the signal wave and 2.1 μm of tunable range for the idler wave.
A Flat-Gain Double-Pass Amplifier with New Hafnia-Bismuth-Erbium Codoped Fiber
Alabbas A. Al-Azzawi, Aya A. Almukhtar, P. H. Reddy, D. Dutta, S. Das, A. Dhar, M. C. Paul, U. N. Zakaria, S. W. Harun
Chin. Phys. Lett. 2018, 35 (5): 054206 .   DOI: 10.1088/0256-307X/35/5/054206
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An efficient and compact double-pass optical fiber amplifier is demonstrated using a newly developed hafnia bismuth erbium co-doped fiber (HBEDF) as a gain medium. The HBEDF is fabricated using a modified chemical vapor deposition in conjunction with solution doping. The fiber has an erbium ion concentration of 12500 ppm. At the optimum length of 0.5 m, the HBEDF amplifier (HBEDFA) achieves a flat gain of 26 dB with a gain variation of less than 1.5 dB within a wavelength region from 1530 to 1560 nm when the input signal and pump power are fixed at $-$30 dBm and 140 mW, respectively. On the other hand, at the input signal power of $-$10 dBm, the HBEDFA also achieves a flat gain of 14.2 dB with a gain variation of less than 2.5 dB within a wide wavelength region from 1525 to 1570 nm. Compared with the conventional zirconia erbium co-doped fiber based amplifier, the proposed HBEDFA obtains a more efficient gain and lower noise figure. For an input signal of $-$30 dBm, the gain improvements of 6.2 dB and 4.8 dB are obtained at 1525 nm and 1540 nm, respectively.
Fabrication of 4-Inch Nano Patterned Wafer with High Uniformity by Laser Interference Lithography
Gen Yue, Yu Lei, Jun-Hui Die, Hai-Qiang Jia, Hong Chen
Chin. Phys. Lett. 2018, 35 (5): 054207 .   DOI: 10.1088/0256-307X/35/5/054207
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We report the fabrication of 4-inch nano patterned wafer by two-beam laser interference lithography and analyze the uniformity in detail. The profile of the dots array with a period of 800 nm divided into five regions is characterized by a scanning electron microscope. The average size in each region ranges from 270 nm to 320 nm, and the deviation is almost 4%, which is approaching the applicable value of 3% in the industrial process. We simulate the two-beam laser interference lithography system with MATLAB software and then calculate the distribution of light intensity around the 4 inch area. The experimental data fit very well with the calculated results. Analysis of the experimental data and calculated data indicates that laser beam quality and space filter play important roles in achieving a periodical nanoscale pattern with high uniformity and large area. There is the potential to obtain more practical applications.
Tunable Band Gap in Piezoelectric Composite Rod Based on the Inter-Coupling Effect
Ze-Qun Fang, Zhi-Lin Hou
Chin. Phys. Lett. 2018, 35 (5): 054601 .   DOI: 10.1088/0256-307X/35/5/054601
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The longitudinal wave propagating in one-dimensional periodic piezoelectric composite rod with inter-coupling between different piezoelectric segments is investigated. The analytical formulae for such a structure are shown and the dispersion relation is calculated. The results show that, by introducing the inter-coupling between the different piezoelectric segments, which is accomplished by serially connecting every $n$ piezoelectric segment into supercells, some tunable Bragg band gaps can accordingly be opened in the low frequency region. The investigation could provide a new guideline for the tunable phononic crystal under passive control.
Weakly Nonlinear Rayleigh–Taylor Instability in Cylindrically Convergent Geometry
Hong-Yu Guo, Li-Feng Wang, Wen-Hua Ye, Jun-Feng Wu, Wei-Yan Zhang
Chin. Phys. Lett. 2018, 35 (5): 055201 .   DOI: 10.1088/0256-307X/35/5/055201
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The Rayleigh–Taylor instability (RTI) in cylindrical geometry is investigated analytically through a second-order weakly nonlinear (WN) theory considering the Bell–Plesset (BP) effect. The governing equations for the combined perturbation growth are derived. The WN solutions for an exponentially convergent cylinder are obtained. It is found that the BP and RTI growths are strongly coupled, which results in the bubble-spike asymmetric structure in the WN stage. The large Atwood number leads to the large deformation of the convergent interface. The amplitude of the spike grows faster than that of the bubble especially for large mode number $m$ and large Atwood number $A$. The averaged interface radius is small for large mode number perturbation due to the mode-coupling effect.
Demonstration of a Shock-Timing Experiment in a CH Layer at the ShenGuang III Laser Facility
Feng WANG, Yu-Long Li, Zhe-Bin Wang, Tao Xu, Wei-Yi Zha, Dong Yang
Chin. Phys. Lett. 2018, 35 (5): 055202 .   DOI: 10.1088/0256-307X/35/5/055202
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Shock-timing experiments are indispensable to inertial confinement fusion mainly because the timing of multiple shock waves is crucial to understanding the processes of laser irradiation of targets. Investigations into shock waves driven by a two-step radiation pulse in polystyrene (CH) capsule targets are experimentally conducted at the ShenGuang III laser facility. Differing from the traditional shock-timing implementation in which one shock wave could catch up with another one in solid CH, in this experiment, the second shock front in a rarefaction CH layer is observed through velocity interferometry. This second shock could also be made to converge with rarefaction waves within only a few micrometers of the CH capsule by designing the two-shock coalescence time. A shock-timing diagnostic technique to tune the multi-shock convergence in the CH capsule can thereby be achieved. The experimental results in the CH layer are quasi-quantitatively interpreted using streamlines simulated with the Multi-1D program. The experimental results are expected to offer important information for target structure and laser pulse design, both of which are important for realizing inertial confinement fusion.
Mechanism of Electromagnetic Flow Control Enhanced by Electro-Discharge in Water
Yan-Liang Ji, Ben-Mou Zhou, Ya-Dong Huang
Chin. Phys. Lett. 2018, 35 (5): 055203 .   DOI: 10.1088/0256-307X/35/5/055203
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Pulsed discharge utilized to achieve large current density in the electromagnetic flow control is numerically studied. A mathematic discharge model is established to calculate the plasma channel, and an actuator is designed to generate the Lorentz force in the micro plasma channel. During the discharge process, the resistance in the channel decreases rapidly and a large current density appears between the discharge electrodes. After the actuator is applied in the leading edge of a flat plate, the separation region and downstream turbulent boundary layer on the plate disappear. Meanwhile, a skin-friction drag force reduction is achieved.
Metastable Electron Traps in Modified Silicon-on-Insulator Wafer
Li-Hua Dai, Da-Wei Bi, Zheng-Xuan Zhang, Xin Xie, Zhi-Yuan Hu, Hui-Xiang Huang, Shi-Chang Zou
Chin. Phys. Lett. 2018, 35 (5): 056101 .   DOI: 10.1088/0256-307X/35/5/056101
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We perform the total ionizing radiation and electrical stress experiments to investigate the electrical characteristics of the modified silicon-on-insulator (SOI) wafers under different Si ion implantation conditions. It is confirmed that Si implantation into the buried oxide can create deep electron traps with large capture cross section to effectively improve the antiradiation capability of the SOI device. It is first proposed that the metastable electron traps accompanied with Si implantation can be avoided by adjusting the peak location of the Si implantation reasonably.
Hardening of an ODS Ferritic Steel after Helium Implantation and Thermal Annealing
Chang-Hao Su, Chong-Hong Zhang, Yi-Tao Yang, Zhao-Nan Ding, Yu-Guang Chen, Akihiko Kimura
Chin. Phys. Lett. 2018, 35 (5): 056102 .   DOI: 10.1088/0256-307X/35/5/056102
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Specimens of an oxide dispersion strengthened (ODS) ferritic steel (15Cr-4Al-0.6Zr-0.1Ti) are implanted with multiple-energy He ions at room temperature to create a damage plateau of 0.4 dpa for the average (corresponding to an He concentration of about 7000 appm) from the near surface to a depth about 1 μm. The specimen is subsequently thermally annealed at 800$^{\circ}\!$C for 1 h in a vacuum so that simple defects can be formed in the as-implanted state that has undergone significant recombination, meanwhile helium bubbles at nano-scale are formed. Hardness of the specimens are tested with the nano-indentation technique. A hardening by 25% is observed. Microstructures of the specimen after irradiation/annealing are investigated with transmission electron microscopy. Helium bubbles are generally located at dislocations and grain boundaries. Using the dispersed barrier strength model, the strength factor of helium bubbles in the ODS ferritic steel is estimated to be between 0.1 and 0.26, which is close to that of helium bubbles in austenitic steels.
Structural Phase Transition and a Mutation of Electron Mobility in Zn$_{x}$Cd$_{1-x}$O Alloys
Ya-Wei Zhang, Kai-Ke Yang, Hui-Xiong Deng
Chin. Phys. Lett. 2018, 35 (5): 056401 .   DOI: 10.1088/0256-307X/35/5/056401
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We investigate the electronic structures and phase stability of ZnO, CdO and the related alloys in rocksalt (B1) and wurzite (B4) crystal, using the first-principle density functional theory within the hybrid functional approximation. By varying the concentration of Zn components from 0% to 100%, we find that the Zn$_{x}$Cd$_{1-x}$O alloy undergoes a phase transition from octahedron to tetrahedron at $x=0.32$, in agreement with the recent experimental findings. The phase transition leads to a mutation of the electron mobility originated from the changes of the effective mass. Our results qualify ZnO/CdO alloy as an attractive candidate for photo-electrochemical and solar cell power applications.
Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots
Hong-Yu Wang, Dan Shan, Ling Xu
Chin. Phys. Lett. 2018, 35 (5): 056801 .   DOI: 10.1088/0256-307X/35/5/056801
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CdTe/CdS quantum dots (QDs) are fabricated on Si nanowires (NWs) substrates with and without Au nanoparticles (NPs). The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence (PL) intensity of CdTe/CdS QD films on Si nanowire substrates with Au NPs is significantly increased, which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to 4.7 ns after introducing Au NPs into Si NWs.
Improvement of Nickel-Stanogermanide Contact Properties by Platinum Interlayer
Wei-Jun Wan, Wei Ren, Xiao-Ran Meng, Yun-Xia Ping, Xing Wei, Zhong-Ying Xue, Wen-Jie Yu, Miao Zhang, Zeng-Feng Di, Bo Zhang
Chin. Phys. Lett. 2018, 35 (5): 056802 .   DOI: 10.1088/0256-307X/35/5/056802
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We report an effective method to improve the formation of nickel stanogermanide (NiGeSn) by the incorporation of a platinum (Pt) interlayer. After the Ni/Pt/GeSn samples are annealed we obtain uniform NiGeSn thin films, which are characterized by means of sheet resistance, atomic force microscopy, scanning electron microscopy, cross-section transmission electron microscopy, and energy dispersive x-ray spectroscopy. These results show that the presence of Pt increases the smoothness and uniform morphology of NiGeSn films.
Crystallization Process of Superlattice-Like Sb/SiO$_{2}$ Thin Films for Phase Change Memory Application
Xiao-Qin Zhu, Rui Zhang, Yi-Feng Hu, Tian-Shu Lai, Jian-Hao Zhang, Hua Zou, Zhi-Tang Song
Chin. Phys. Lett. 2018, 35 (5): 056803 .   DOI: 10.1088/0256-307X/35/5/056803
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After compositing with SiO$_{2}$ layers, it is shown that superlattice-like Sb/SiO$_{2}$ thin films have higher crystallization temperature ($\sim240^{\circ}\!$C), larger crystallization activation energy (6.22 eV), and better data retention ability (189$^{\circ}\!$C for 10 y). The crystallization of Sb in superlattice-like Sb/SiO$_{2}$thin films is restrained by the multilayer interfaces. The reversible resistance transition can be achieved by an electric pulse as short as 8 ns for the Sb(3 nm)/SiO$_{2}$(7 nm)-based phase change memory cell. A lower operation power consumption of 0.09 mW and a good endurance of $3.0\times10^{6}$ cycles are achieved. In addition, the superlattice-like Sb(3 nm)/SiO$_{2}$(7 nm) thin film shows a low thermal conductivity of 0.13 W/(m$\cdot$K).
Atomic-Ordering-Induced Quantum Phase Transition between Topological Crystalline Insulator and $Z_{2}$ Topological Insulator
Hui-Xiong Deng, Zhi-Gang Song, Shu-Shen Li, Su-Huai Wei, Jun-Wei Luo
Chin. Phys. Lett. 2018, 35 (5): 057301 .   DOI: 10.1088/0256-307X/35/5/057301
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Topological phase transition in a single material usually refers to transitions between a trivial band insulator and a topological Dirac phase, and the transition may also occur between different classes of topological Dirac phases. It is a fundamental challenge to realize quantum transition between $Z_{2}$ nontrivial topological insulator (TI) and topological crystalline insulator (TCI) in one material because $Z_{2}$ TI and TCI have different requirements on the number of band inversions. The $Z_{2}$ TIs must have an odd number of band inversions over all the time-reversal invariant momenta, whereas the newly discovered TCIs, as a distinct class of the topological Dirac materials protected by the underlying crystalline symmetry, owns an even number of band inversions. Taking PbSnTe$_{2}$ alloy as an example, here we demonstrate that the atomic-ordering is an effective way to tune the symmetry of the alloy so that we can electrically switch between TCI phase and $Z_{2}$ TI phase in a single material. Our results suggest that the atomic-ordering provides a new platform towards the realization of reversibly switching between different topological phases to explore novel applications.
Improvement of Operation Characteristics for MONOS Charge Trapping Flash Memory with SiGe Buried Channel
Zhao-Zhao Hou, Gui-Lei Wang, Jia-Xin Yao, Qing-Zhu Zhang, Hua-Xiang Yin
Chin. Phys. Lett. 2018, 35 (5): 057302 .   DOI: 10.1088/0256-307X/35/5/057302
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We propose and investigate a novel metal/SiO$_{2}$/Si$_{3}$N$_{4}$/SiO$_{2}$/SiGe charge trapping flash memory structure (named as MONOS), utilizing SiGe as the buried channel. The fabricated memory device demonstrates excellent program-erasable characteristics attributed to the fact that more carriers are generated by the smaller bandgap of SiGe during program/erase operations. A flat-band voltage shift 2.8 V can be obtained by programming at +11 V for 100 μs. Meanwhile, the memory device exhibits a large memory window of $\sim$7.17 V under $\pm$12 V sweeping voltage, and a negligible charge loss of 18% after 10$^{4}$ s' retention. In addition, the leakage current density is lower than $2.52\times10^{-7}$ A$\cdot$cm$^{-2}$ below a gate breakdown voltage of 12.5 V. Investigation of leakage current-voltage indicates that the Schottky emission is the predominant conduction mechanisms for leakage current. These desirable characteristics are ascribed to the higher trap density of the Si$_{3}$N$_{4}$ charge trapping layer and the better quality of the interface between the SiO$_{2}$ tunneling layer and the SiGe buried channel. Therefore, the application of the SiGe buried channel is very promising to construct 3D charge trapping NAND flash devices with improved operation characteristics.
Electroluminescence from the InGaN/GaN Superlattices Interlayer of Yellow LEDs with Large V-Pits Grown on Si (111)
Xi-xia Tao, Chun-lan Mo, Jun-lin Liu, Jian-li Zhang, Xiao-lan Wang, Xiao-ming Wu, Long-quan Xu, Jie Ding, Guang-xu Wang, Feng-yi Jiang
Chin. Phys. Lett. 2018, 35 (5): 057303 .   DOI: 10.1088/0256-307X/35/5/057303
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A blue emission originated from InGaN/GaN superlattice (SL) interlayer is observed in the yellow LEDs with V-pits embedded in the quantum wells (QWs), revealing that sufficient holes have penetrated through the QWs into SLs far away from the p-type layer. In the V-pits embedded LEDs, hole transport has two paths: via the flat $c$-plane region or via the sidewalls of V-pits. It is proved that the holes in SLs are injected from the sidewalls of V-pits, and the transportation process is significantly affected by working temperature, current density, and the size of V-pits. Four motion possibilities are discussed when the holes flow via the sidewalls. All these may contribute to a better understanding of hole transport and device design.
Coexistence of Polaronic States and Superconductivity in Iron-Pnictide Compound Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O
Li-Yuan Rong, Xun Shi, Pierre Richard, Yun-Lei Sun, Guang-Han Cao, Xiang-Zhi Zhang, Jun-Zhang Ma, Ming Shi, Yao-Bo Huang, Tian Qian, Hong Ding, Ren-Zhong Tai
Chin. Phys. Lett. 2018, 35 (5): 057401 .   DOI: 10.1088/0256-307X/35/5/057401
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The electronic structure of iron-pnictide compound superconductor Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O, which has metallic intermediate Ti$_{2}$O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a 'peak-dip-hump' line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below $T_{\rm c}$ ($\sim$21 K). Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.
Electronic Phase Separation in Iron Selenide (Li,Fe)OHFeSe Superconductor System
Yiyuan Mao, Jun Li, Yulong Huan, Jie Yuan, Zi-an Li, Ke Chai, Mingwei Ma, Shunli Ni, Jinpeng Tian, Shaobo Liu, Huaxue Zhou, Fang Zhou, Jianqi Li, Guangming Zhang, Kui Jin, Xiaoli Dong, Zhongxian Zhao
Chin. Phys. Lett. 2018, 35 (5): 057402 .   DOI: 10.1088/0256-307X/35/5/057402
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The phenomenon of phase separation into antiferromagnetic (AFM) and superconducting (SC) or normal-state regions has great implication for the origin of high-temperature (high-$T_{\rm c}$) superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the $T_{\rm c}$ of (Li,Fe)OHFeSe superconductor is questioned. Here we report a systematic study on a series of (Li,Fe)OHFeSe single crystal samples with $T_{\rm c}$ up to $\sim$41 K. We observe an evident drop in the static magnetization at $T_{\rm afm} \sim 125$ K, in some of the SC ($T_{\rm c} \lesssim 38$ K, cell parameter $c \lesssim 9.27$ Å) and non-SC samples. We verify that this AFM signal is intrinsic to (Li,Fe)OHFeSe. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal (below $T_{\rm afm}$) or SC (below $T_{\rm c}$) state in (Li,Fe)OHFeSe. We explain such coexistence by electronic phase separation, similar to that in high-$T_{\rm c}$ cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of (Li,Fe)OHFeSe, particularly it is never observed in the SC samples of $T_{\rm c} \gtrsim 38$ K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. The occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as $T_{\rm afm}$, reported previously for a (Li,Fe)OHFeSe ($T_{\rm c} \sim 42$ K) single crystal, suggests that the microscopic static phase separation reaches vanishing point in high-$T_{\rm c}$ (Li,Fe)OHFeSe. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-$T_{\rm c}$ superconductivity.
Shape Anisotropy and Resonance Mode Guided Reliable Interconnect Design for In-plane Magnetic Logic
Xiao-Kuo Yang, Bin Zhang, Jia-Hao Liu, Ming-Liang Zhang, Wei-Wei Li, Huan-Qing Cui, Bo Wei
Chin. Phys. Lett. 2018, 35 (5): 057501 .   DOI: 10.1088/0256-307X/35/5/057501
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Dipole coupled nanomagnets controlled by the static Zeeman field can form various magnetic logic interconnects. However, the corner wire interconnect is often unreliable and error-prone at room temperature. In this study, we address this problem by making it into a reliable type with trapezoid-shaped nanomagnets, the shape anisotropy of which helps to offer the robustness. The building method of the proposed corner wire interconnect is discussed, and both its static and dynamic magnetization properties are investigated. Static micromagnetic simulation demonstrates that it can work correctly and reliably. Dynamic response results are reached by imposing an ac microwave field on the proposed corner wire. It is found that strong ferromagnetic resonance absorption appears at a low frequency. With the help of a very small ac field with the peak resonance frequency, the required static Zeeman field to switch the corner wire is significantly decreased by $\sim$21 mT. This novel interconnect would pave the way for the realization of reliable and low power nanomagnetic logic circuits.
Band Structure and Optical Gain of InGaAs/GaAsBi Type-II Quantum Wells Modeled by the $k\cdot p$ Model
Chang Wang, Wenwu Pan, Konstantin Kolokolov, Shumin Wang
Chin. Phys. Lett. 2018, 35 (5): 057801 .   DOI: 10.1088/0256-307X/35/5/057801
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Optical gains of type-II InGaAs/GaAsBi quantum wells (QWs) with W, N, and M shapes are analyzed theoretically for near-infrared laser applications. The bandgap and wave functions are calculated using the self-consistent $k\cdot p$ Hamiltonian, taking into account valence band mixing and the strain effect. Our calculations show that the M-shaped type-II QWs are a promising structure for making 1.3 μm lasers at room temperature because they can easily be used to obtain 1.3 μm for photoluminescence with a proper thickness and have large wave-function overlap for high optical gain.
Curbing Charging Currents in Pulsed Field Emission by Prolonging Pulse Edges
Jin-Di Wei, Yun-Hui Li, Geng-Min Zhang, Jin Yang, Ying-Jie Xing, Wen-Sheng Zhou
Chin. Phys. Lett. 2018, 35 (5): 057901 .   DOI: 10.1088/0256-307X/35/5/057901
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In field emission under a non-dc voltage, a displacement current is inevitable due to charging the cathode–anode condenser. Under an often-used square voltage pulse, in which the voltage rises from zero to a certain value abruptly, the charging current in the circuit is very large at the rising and falling edges. This large charging current makes measurement of the actual emissive current from the cathode difficult, constitutes a threat to the components in the circuit and causes attenuation of the emissive current within the pulse. To alleviate these drawbacks, trapezoid voltage pulses, whose rising edges are extended dramatically in comparison with square voltage pulses, are employed to extract the field emission. Under a trapezoid voltage pulse, the charging current is clearly lowered as expected. Furthermore, the heat generated by the charging current under the trapezoid voltage pulse is much smaller than that under the square voltage pulse. Hence the emissive current does not show any attenuation within the pulse. Finally, the average emissive currents are found to decrease with the repetition frequency of the pulses.
Growth of $\beta$-Ga$_{2}$O$_{3}$ Films on Sapphire by Hydride Vapor Phase Epitaxy
Ze-Ning XIONG, Xiang-Qian XIU, Yue-Wen LI, Xue-Mei HUA, Zi-Li XIE, Peng CHEN, Bin LIU, Ping HAN, Rong ZHANG, You-Dou ZHENG
Chin. Phys. Lett. 2018, 35 (5): 058101 .   DOI: 10.1088/0256-307X/35/5/058101
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Two-inch Ga$_{2}$O$_{3}$ films with ($\bar{2}$01)-orientation are grown on $c$-sapphire at 850–1050$^{\circ}\!$C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure $\beta$-Ga$_{2}$O$_{3}$ with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in $\beta$-Ga$_{2}$O$_{3}$ grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 eV.
A Simpler Memristor Emulator Based on Varactor Diode
Dong-Sheng Yu, Ting-Ting Sun, Ci-Yan Zheng, H. H. C. Iu, T. Fernando
Chin. Phys. Lett. 2018, 35 (5): 058401 .   DOI: 10.1088/0256-307X/35/5/058401
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A new memristor (MR) emulator is designed by making use of only three current-feedback operational amplifiers, one varactor diode, one capacitor and five resistors. As compared with other reported MR emulators, only three active devices and ten components in total are required for realizing this MR emulator, and hence this emulator can be regarded as a simpler one for the moment. The results obtained by Multisim simulation and experimental prototypes are given to verify the practicality and feasibility of this MR emulator.
Human Pulmonary Hyperpolarized $^{129}$Xe MRI: a Preliminary Study
Hao Yang, Ke Wang, Hui-Ting Zhang, Jun-Shuai Xie, Guang-Yao Wu, Xin Zhou
Chin. Phys. Lett. 2018, 35 (5): 058701 .   DOI: 10.1088/0256-307X/35/5/058701
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We study the feasibility and safety of human lung hyperpolarized (HP) $^{129}$Xe magnetic resonance imaging (MRI). There is no significant change in physiological parameters before and after the examinations of all subjects. Compared with computed tomography, HP $^{129}$Xe MRI is sensitive to earlier and smaller ventilation defects. The distribution of the HP $^{129}$Xe MRI signal reflects the pulmonary compliance with the gravity gradient. This is the first application of HP $^{129}$Xe MRI ventilation imaging in China, and this technology is expected to provide more useful information for clinical practice.
Frequency Switches at Transition Temperature in Voltage-Gated Ion Channel Dynamics of Neural Oscillators
Yasuomi D. Sato
Chin. Phys. Lett. 2018, 35 (5): 058702 .   DOI: 10.1088/0256-307X/35/5/058702
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Understanding of the mechanisms of neural phase transitions is crucial for clarifying cognitive processes in the brain. We investigate a neural oscillator that undergoes different bifurcation transitions from the big saddle homoclinic orbit type to the saddle node on an invariant circle type, and the saddle node on an invariant circle type to the small saddle homoclinic orbit type. The bifurcation transitions are accompanied by an increase in thermodynamic temperature that affects the voltage-gated ion channel in the neural oscillator. We show that nonlinear and thermodynamical mechanisms are responsible for different switches of the frequency in the neural oscillator. We report a dynamical role of the phase response curve in switches of the frequency, in terms of slopes of frequency-temperature curve at each bifurcation transition. Adopting the transition state theory of voltage-gated ion channel dynamics, we confirm that switches of the frequency occur in the first-order phase transition temperature states and exhibit different features of their potential energy derivatives in the ion channel. Each bifurcation transition also creates a discontinuity in the Arrhenius plot used to compute the time constant of the ion channel.
Anomaly Detection of Complex Networks Based on Intuitionistic Fuzzy Set Ensemble
Jin-Fa Wang, Xiao Liu, Hai Zhao, Xing-Chi Chen
Chin. Phys. Lett. 2018, 35 (5): 058901 .   DOI: 10.1088/0256-307X/35/5/058901
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Ensemble learning for anomaly detection of data structured into a complex network has been barely studied due to the inconsistent performance of complex network characteristics and the lack of inherent objective function. We propose the intuitionistic fuzzy set (IFS)-based anomaly detection, a new two-phase ensemble method for anomaly detection based on IFS, and apply it to the abnormal behavior detection problem in temporal complex networks. Firstly, it constructs the IFS of a single network characteristic, which quantifies the degree of membership, non-membership and hesitation of each network characteristic to the defined linguistic variables so that makes the unuseful or noise characteristics become part of the detection. To build an objective intuitionistic fuzzy relationship, we propose a Gaussian distribution-based membership function which gives a variable hesitation degree. Then, for the fuzzification of multiple network characteristics, the intuitionistic fuzzy weighted geometric operator is adopted to fuse multiple IFSs and to avoid the inconsistence of multiple characteristics. Finally, the score function and precision function are used to sort the fused IFS. Finally, we carry out extensive experiments on several complex network datasets for anomaly detection, and the results demonstrate the superiority of our method to state-of-the-art approaches, validating the effectiveness of our method.
36 articles