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Experimental Realization of an Intrinsic Magnetic Topological Insulator
Yan Gong, Jingwen Guo, Jiaheng Li, Kejing Zhu, Menghan Liao, Xiaozhi Liu, Qinghua Zhang, Lin Gu, Lin Tang, Xiao Feng, Ding Zhang, Wei Li, Canli Song, Lili Wang, Pu Yu, Xi Chen, Yayu Wang, Hong Yao, Wenhui Duan, Yong Xu, Shou-Cheng Zhang, Xucun Ma, Qi-Kun Xue, Ke He
Chin. Phys. Lett.    2019, 36 (7): 076801.   DOI: 10.1088/0256-307X/36/7/076801
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An intrinsic magnetic topological insulator (TI) is a stoichiometric magnetic compound possessing both inherent magnetic order and topological electronic states. Such a material can provide a shortcut to various novel topological quantum effects but remained elusive experimentally for a long time. Here we report the experimental realization of thin films of an intrinsic magnetic TI, MnBi$_{2}$Te$_{4}$, by alternate growth of a Bi$_{2}$Te$_{3}$ quintuple layer and a MnTe bilayer with molecular beam epitaxy. The material shows the archetypical Dirac surface states in angle-resolved photoemission spectroscopy and is demonstrated to be an antiferromagnetic topological insulator with ferromagnetic surfaces by magnetic and transport measurements as well as first-principles calculations. The unique magnetic and topological electronic structures and their interplays enable the material to embody rich quantum phases such as quantum anomalous Hall insulators and axion insulators at higher temperature and in a well-controlled way.
Discovery of Fractionalized Neutral Spin-1/2 Excitation of Topological Order
Xiao-Gang Wen
Chin. Phys. Lett.    2017, 34 (9): .   DOI: 10.1088/0256-307X/34/9/090101
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Rear-Surface Deformation of a Water Drop in Aero-Breakup of Shear Mode
Xiang-Yu Yi, Yu-Jian Zhu, Ji-Ming Yang, Tun Wang, Ming-Yu Sun
Chin. Phys. Lett.    2017, 34 (8): .   DOI: 10.1088/0256-307X/34/8/084701
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Deformation of water drops in shock-induced high-speed flows is investigated with a focus to the influence of primitive flow parameters on the rear-surface deformation features. Two typical deformation patterns are discovered through high-speed photography. A simple equation to evaluate the radial acceleration of the drop surface is derived. The combined use of this equation and outer flow simulation makes it possible for us to reconstruct the profiles of the early deformed drops. The results agree well with the experiments. Further analysis shows that the duration of flow establishment with respect to the overall breakup time shapes the rear side profile of the drop. Thereby the ratio of the two times, expressed as the square root of the density ratio, appears to be an effective indicator of the deformation features.
Erbium-Doped Zirconia-Alumina Silica Glass-Based Fiber as a Saturable Absorber for High Repetition Rate Q-Switched All-Fiber Laser Generation
P. Harshavardhan Reddy, N. A. A. Kadir, M. C. Paul, S. Das, A. Dhar, E. I. Ismail, A. A. Latiff, S. W. Harun
Chin. Phys. Lett.    2017, 34 (8): .   DOI: 10.1088/0256-307X/34/8/084203
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We propose and demonstrate a Q-switched erbium-doped fiber laser (EDFL) using an erbium-doped zirconia-alumina silica glass-based fiber (Zr-EDF) as a saturable absorber. As a 16-cm-long Zr-EDF is incorporated into a ring EDFL cavity, a stable Q-switching pulse train operating at 1565 nm wavelength is successfully obtained. The repetition rate is tunable from 33.97 kHz to 71.23 kHz by increasing the pump power from the threshold of 26 mW to the maximum of 74 mW. The highest pulse energy of 26.67 nJ is obtained at the maximum pump power.
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): .   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.
Numerical Analysis of Magnetic-Shielding Effectiveness for Magnetic Resonant Wireless Power Transfer System
Wei-Guo Lu, Hui-Rong Li, Wei-Ming Chen, Li-Hui Liu
Chin. Phys. Lett.    2017, 34 (8): .   DOI: 10.1088/0256-307X/34/8/088801
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Magnetic radiation phenomena appear inevitably in the magnetic-resonance wireless power transfer (MR-WPT) system, and regarding this problem the magnetic-shielding scheme is applied to improve the electromagnetic performance in engineering. In this study, the shielding effectiveness of a two-coil MR-WPT system for different material shields is analyzed in theory using Moser's formula and Schelkunoff's formula. On this basis a candidate magnetic-shielding scheme with a double-layer structure is determined, which has better shielding effectiveness and coils coupling coefficient. Finally, some finite element simulation results validate the correctness of the theoretical analysis, and the shielding effectiveness with the double-layer shield in maximum is 30 dB larger than the one with the single-layer case.
Molybdenum Carbide: A Stable Topological Semimetal with Line Nodes and Triply Degenerate Points
Jian-Peng Sun, Dong Zhang, Kai Chang
Chin. Phys. Lett.    2017, 34 (2): 027102.   DOI: 10.1088/0256-307X/34/2/027102
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We propose that the hexagonal crystal form of MoC is a stable and new type of topological semimetal. It hosts an exotic Fermi surface consisting of two concentric nodal rings in the presence of spin-orbit coupling, and possesses four pairs of triply degenerate points (TDPs) in the vicinity of the Fermi energy. The coexistence of the nodal ring Fermi surface and TDPs in MoC leads to extraordinary properties such as distinguishable drumhead surface states and manipulatable new fermions, which make MoC a fertile platform for in-depth understanding of topological phenomena and a potential candidate material for topological electronic devices.
Micromagnetic Studies of Finite Temperature $M$–$H$ Loops for FePt-C Media
Long-Ze Wang, Jing-Yue Miao, Zhen Zhao, Chuan Liu, Dan Wei
Chin. Phys. Lett.    2017, 34 (2): 027501.   DOI: 10.1088/0256-307X/34/2/027501
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We have recently developed a new micromagnetic method at finite temperature, where the Hybrid Monte Carlo method is employed to realize the Boltzmann distribution with respect to the magnetic free energy. Hence, the hysteresis loops and domain structures at arbitrary temperature below the Curie point $T_{\rm c}$ can be simulated. The Hamilton equations are used to find the magnetization distributions instead of the Landau–Lifshitz (LL) equations. In our previous work, we applied this method on a simple uniaxial anisotropy nano-particle and compared it with the micromagnetic method using LL equations. In this work, we use this new method to simulate an L10 FePt-C granular thin film at finite temperatures. The polycrystalline Voronoi microstructure is included in the model, and the effects of the misorientation of FePt grains are also simulated.
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.
Note on Divergence of the Chapman–Enskog Expansion for Solving Boltzmann Equation
Nan-Xian Chen, Bo-Hua Sun
Chin. Phys. Lett.    2017, 34 (2): 020502.   DOI: 10.1088/0256-307X/34/2/020502
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Within about a year (1916–1917) Chapman and Enskog independently proposed an important expansion for solving the Boltzmann equation. However, the expansion is divergent or indeterminant in the case of relaxation time $\tau \geq 1$. Since then, this divergence problem has puzzled researchers for a century. Using a modified Möbius series inversion formula, we propose a modified Chapman–Enskog expansion with a variable upper limit of the summation. The new expansion can give not only a convergent summation but also the best-so-far explanation on some unbelievable scenarios occurring in previous practice.
A New Fractional Model for the Falling Body Problem
A. Ebaid, B. Masaedeh, E. El-Zahar
Chin. Phys. Lett.    2017, 34 (2): 020201.   DOI: 10.1088/0256-307X/34/2/020201
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Recently, a conformable fractional derivative has been proposed to calculate the derivative of non-integer order of time functions. It has been shown that this new fractional derivative definition obeys many advantages over the preceding definitions. For mathematical models in applied sciences and to preserve the dimensionality of the physical quantities, an auxiliary parameter ($\sigma$) which has the dimension of seconds should be implemented in the fractional derivative definition. We obtain analytic solutions for the resulting conformable fractional differential equations describing the vertical velocity and the height of the falling body. It is shown that the dimensions of velocity and height are always correct without any restrictions on the auxiliary parameter $\sigma$ which contradicts with the results in the literature when applying the Caputo definition to the same problem. This may open the door for many future works either to describe the role of such an auxiliary parameter or to derive a more suitable definition for the fractional derivative.
Electronic, Elastic and Piezoelectric Properties of Two-Dimensional Group-IV Buckled Monolayers
Jing Shi, Yong Gao, Xiao-Li Wang, Si-Ning Yun
Chin. Phys. Lett.    2017, 34 (8): .   DOI: 10.1088/0256-307X/34/8/087701
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Electronic, elastic and piezoelectric properties of two-dimensional (2D) group-IV buckled monolayers (GeSi, SnSi and SnGe) are studied by first principle calculations. According to our calculations, SnSi and SnGe are good 2D piezoelectric materials with large piezoelectric coefficients. The values of $d_{11}$ of SnSi and SnGe are 5.04 pm/V and 5.42 pm/V, respectively, which are much larger than 2D MoS$_{2}$ (3.6 pm/V) and are comparable with some frequently used bulk materials (e.g., wurtzite AlN 5.1 pm/V). Charge transfer is calculated by the Löwdin analysis and we find that the piezoelectric coefficients ($d_{11}$ and $d_{31}$) are highly dependent on the polarizabilities of the anions and cations in group-IV monolayers.
Lorentz Force Electrical Impedance Detection Using Step Frequency Technique
Zhi-Shen Sun, Guo-Qiang Liu, Hui Xia
Chin. Phys. Lett.    2018, 35 (1): .   DOI: 10.1088/0256-307X/35/1/014301
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Lorentz force electrical impedance tomography (LFEIT) inherits the merit of high resolution by ultrasound stimulation and the merit of high contrast through electromagnetic field detection. To reduce the instantaneous peak power of the stimulating signal to the transducer, the sinusoidal pulse and step-frequency technique is investigated in LFEIT. The theory of application of step-frequency technique in LFEIT is formulated with the direct demodulation method and the in-phase quadrature demodulation method. Compared with the in-phase quadrature demodulation method, the direct demodulation method has simple experimental setup but could only detect half of the range. Experiments carried out with copper foils confirmed that LFEIT using the step-frequency technique could detect the electrical conductivity variations precisely, which suggests an alternative method of realization of LFEIT.
Rogue Waves in the (2+1)-Dimensional Nonlinear Schrödinger Equation with a Parity-Time-Symmetric Potential
Yun-Kai Liu, Biao Li
Chin. Phys. Lett.    2017, 34 (1): 010202.   DOI: 10.1088/0256-307X/34/1/010202
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The (2+1)-dimension nonlocal nonlinear Schrödinger (NLS) equation with the self-induced parity-time symmetric potential is introduced, which provides spatially two-dimensional analogues of the nonlocal NLS equation introduced by Ablowitz et al. [Phys. Rev. Lett. 110 (2013) 064105]. General periodic solutions are derived by the bilinear method. These periodic solutions behave as growing and decaying periodic line waves arising from the constant background and decaying back to the constant background again. By taking long wave limits of the obtained periodic solutions, rogue waves are obtained. It is also shown that these line rogue waves arise from the constant background with a line profile and disappear into the constant background again in the $(x,y)$ plane.
High Refractive Index Ti$_3$O$_5$ Films for Dielectric Metasurfaces
Sohail Abdul Jalil, Mahreen Akram, Gwanho Yoon, Ayesha Khalid, Dasol Lee, Niloufar Raeis-Hosseini, Sunae So, Inki Kim, Qazi Salman Ahmed, Junsuk Rho, Muhammad Qasim Mehmood
Chin. Phys. Lett.    2017, 34 (8): .   DOI: 10.1088/0256-307X/34/8/088102
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Ti$_3$O$_5$ films are deposited with the help of an electron beam evaporator for their applications in metasurfaces. The film of subwavelength (632 nm) thickness is deposited on a silicon substrate and annealed at 400$^{\circ}\!$C. The ellipsometry result shows a high refractive index above 2.5 with the minimum absorption coefficient in the visible region, which is necessary for high efficiency of transparent metasurfaces. Atomic force microscopy analysis is employed to measure the roughness of the as-deposited films. It is seen from micrographs that the deposited films are very smooth with the minimum roughness to prevent scattering and absorption losses for metasurface devices. The absence of grains and cracks can be seen by scanning electron microscope analysis, which is favorable for electron beam lithography. Fourier transform infrared spectroscopy reveals the transmission and reflection obtained from the film deposited on glass substrates. The as-deposited film shows high transmission above 60%, which is in good agreement with metasurfaces.
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.
Thermoluminescence Kinetic Parameters of TLD-600 and TLD-700 after $^{252}$Cf Neutron+Gamma and $^{90}$Sr-$^{90}$Y Beta Radiations
S. İflazoğlu, V. E. Kafadar, B. Yazici, A. N. Yazici
Chin. Phys. Lett.    2017, 34 (1): 017801.   DOI: 10.1088/0256-307X/34/1/017801
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The thermoluminescent (TL) properties such as glow curve structure, relative thermoluminescence sensitivity, dose response linearity of lithium fluoride thermoluminescent dosimeters $^{6}$LiF:Ti,Mg (TLD-600) and $^{7}$LiF:Ti,Mg (TLD-700) are investigated after irradiation $^{252}$Cf neutron+gamma and $^{90}$Sr-$^{90}$Y beta sources at room temperature and then the obtained results are compared. The kinetic parameters, namely the order of kinetics $b$, activation energy $E_{\rm a}$ and the frequency factor $s$, are calculated using the computerized glow curve deconvolution (CGCD) program. The effect of heating rate on the glow curves of dosimeters is also investigated. The maximum TL peak intensities and the total area under the glow curves decrease with the increasing heating rate. There is no agreement with the kinetic parameters calculated by the CGCD program for both radiation sources.
Two-Dimensional Node-Line Semimetals in a Honeycomb-Kagome Lattice
Jin-Lian Lu, Wei Luo, Xue-Yang Li, Sheng-Qi Yang, Jue-Xian Cao, Xin-Gao Gong, Hong-Jun Xiang
Chin. Phys. Lett.    2017, 34 (5): 057302.   DOI: 10.1088/0256-307X/34/5/057302
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Recently, the concept of topological insulators has been generalized to topological semimetals, including three-dimensional (3D) Weyl semimetals, 3D Dirac semimetals, and 3D node-line semimetals (NLSs). In particular, several compounds (e.g., certain 3D graphene networks, Cu$_{3}$PdN, Ca$_{3}$P$_{2}$) were discovered to be 3D NLSs, in which the conduction and valence bands cross at closed lines in the Brillouin zone. Except for the two-dimensional (2D) Dirac semimetal (e.g., graphene), 2D topological semimetals are much less investigated. Here we propose a new concept of a 2D NLS and suggest that this state could be realized in a new mixed lattice (named as HK lattice) composed by Kagome and honeycomb lattices. It is found that A$_{3}$B$_{2}$ (A is a group-IIB cation and B is a group-VA anion) compounds (such as Hg$_{3}$As$_{2})$ with the HK lattice are 2D NLSs due to the band inversion between the cation Hg-$s$ orbital and the anion As-$p_{z}$ orbital with respect to the mirror symmetry. Since the band inversion occurs between two bands with the same parity, this peculiar 2D NLS could be used as transparent conductors. In the presence of buckling or spin-orbit coupling, the 2D NLS state may turn into a 2D Dirac semimetal state or a 2D topological crystalline insulating state. Since the band gap opening due to buckling or spin-orbit coupling is small, Hg$_{3}$As$_{2}$ with the HK lattice can still be regarded as a 2D NLS at room temperature. Our work suggests a new route to design topological materials without involving states with opposite parities.
Characterization of Interface State Density of Ni/p-GaN Structures by Capacitance/Conductance-Voltage-Frequency Measurements
Zhi-Fu Zhu, He-Qiu Zhang, Hong-Wei Liang, Xin-Cun Peng, Ji-Jun Zou, Bin Tang, Guo-Tong Du
Chin. Phys. Lett.    2017, 34 (9): .   DOI: 10.1088/0256-307X/34/9/097301
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For the frequency range of 1 kHz–10 MHz, the interface state density of Ni contacts on p-GaN is studied using capacitance-voltage ($C$–$V$) and conductance-frequency-voltage ($G$–$f$–$V$) measurements at room temperature. To obtain the real capacitance and interface state density of the Ni/p-GaN structures, the effects of the series resistance ($R_{\rm s}$) on high-frequency (5 MHz) capacitance values measured at a reverse and a forward bias are investigated. The mean interface state densities obtained from the $C_{\rm HF}$–$C_{\rm LF}$ capacitance and the conductance method are $2\times10^{12}$ eV$^{-1}$cm$^{-2}$ and $0.94\times10^{12}$ eV$^{-1}$cm$^{-2}$, respectively. Furthermore, the interface state density derived from the conductance method is higher than that reported from the Ni/n-GaN in the literature, which is ascribed to a poor crystal quality and to a large defect density of the Mg-doped p-GaN.
Electrically Tunable Energy Bandgap in Dual-Gated Ultra-Thin Black Phosphorus Field Effect Transistors
Shi-Li Yan, Zhi-Jian Xie, Jian-Hao Chen, Takashi Taniguchi, Kenji Watanabe
Chin. Phys. Lett.    2017, 34 (4): 047304.   DOI: 10.1088/0256-307X/34/4/047304
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The energy bandgap is an intrinsic character of semiconductors, which largely determines their properties. The ability to continuously and reversibly tune the bandgap of a single device during real time operation is of great importance not only to device physics but also to technological applications. Here we demonstrate a widely tunable bandgap of few-layer black phosphorus (BP) by the application of vertical electric field in dual-gated BP field-effect transistors. A total bandgap reduction of 124 meV is observed when the electrical displacement field is increased from 0.10 V/nm to 0.83 V/nm. Our results suggest appealing potential for few-layer BP as a tunable bandgap material in infrared optoelectronics, thermoelectric power generation and thermal imaging.
Pressure-Induced Metallization Accompanied by Elongated S–S Dimer in Charge Transfer Insulator NiS$_{2}$
Hao Wu, Yong-Hui Zhou, Yi-Fang Yuan, Chun-Hua Chen, Ying Zhou, Bo-Wen Zhang, Xu-Liang Chen, Chuan-Chuan Gu, Chao An, Shu-Yang Wang, Meng-Yao Qi, Ran-Ran Zhang, Li-Li Zhang, Xin-Jian Li, Zhao-Rong Yang
Chin. Phys. Lett.    2019, 36 (10): .   DOI: 10.1088/0256-307X/36/10/107101
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The insulator-metal transition triggered by pressure in charge transfer insulator NiS$_{2}$ is investigated by combining high-pressure electrical transport, synchrotron x-ray diffraction and Raman spectroscopy measurements up to 40–50 GPa. Upon compression, we show that the metallization firstly appears in the low temperature region at $\sim$3.2 GPa and then extends to room temperature at $\sim $8.0 GPa. During the insulator-metal transition, the bond length of S–S dimer extracted from the synchrotron x-ray diffraction increases with pressure, which is supported by the observation of abnormal red-shift of the Raman modes between 3.2 and 7.1 GPa. Considering the decreasing bonding-antibonding splitting due to the expansion of S–S dimer, the charge gap between the S-$pp\pi^*$ band and the upper Hubbard band of Ni-3$d$ $e_{\rm g}$ state is remarkably decreased. These results consistently indicate that the elongated S–S dimer plays a predominant role in the insulator-metal transition under high pressure, even though the $p$-$d$ hybridization is enhanced simultaneously, in accordance with a scenario of charge-gap-controlled type.
Total Ionizing Dose Radiation Effects in the P-Type Polycrystalline Silicon Thin Film Transistors
Yuan Liu, Kai Liu, Rong-Sheng Chen, Yu-Rong Liu, Yun-Fei En, Bin Li, Wen-Xiao Fang
Chin. Phys. Lett.    2017, 34 (1): 018501.   DOI: 10.1088/0256-307X/34/1/018501
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The total ionizing dose radiation effects in the polycrystalline silicon thin film transistors are studied. Transfer characteristics, high-frequency capacitance-voltage curves and low-frequency noises (LFN) are measured before and after radiation. The experimental results show that threshold voltage and hole-field-effect mobility decrease, while sub-threshold swing and low-frequency noise increase with the increase of the total dose. The contributions of radiation induced interface states and oxide trapped charges to the shift of threshold voltage are also estimated. Furthermore, spatial distributions of oxide trapped charges before and after radiation are extracted based on the LFN measurements.
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): .   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.
Refractive Plasmonic Sensor Based on Fano Resonances in an Optical System
Wei-Jie Mai, Yi-Lin Wang, Yun-Yun Zhang, Lu-Na Cui, Li Yu
Chin. Phys. Lett.    2017, 34 (2): 024204.   DOI: 10.1088/0256-307X/34/2/024204
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A symmetric plasmonic structure consisting of metal–insulator–metal waveguide, groove and slot cavities is studied, which supports double Fano resonances deriving from two different mechanisms. One of the Fano resonances originates from the interference between the resonances of groove and slot cavities, and the other comes from the interference between slot cavities. The spectral line shapes and the peaks of the double Fano resonances can be modulated by changing the length of the slot cavities and the height of the groove. Furthermore, the wavelength of the resonance peak has a linear relationship with the length of the slot cavities. The proposed plasmonic nanosensor possesses a sensitivity of 800 nm/RIU and a figure of merit of 3150, which may have important applications in switches, sensors, and nonlinear devices.
Ion-Beam-Induced Luminescence of LiF Using Negative Ions
Meng-Lin Qiu, Ying-Jie Chu, Guang-Fu Wang, Mi Xu, Li Zheng
Chin. Phys. Lett.    2017, 34 (1): 016104.   DOI: 10.1088/0256-307X/34/1/016104
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Negative ion-beam-induced luminescence (IBIL) measurements of a pure LiF crystal using 20 keV H$^{-}$ are performed to monitor the formation and annihilation of luminescence centers during ion irradiation. Several emission bands are observed in the IBIL spectra and the evolvement mechanisms of the corresponding centers are identified. The difference between the IBIL measurements using positive ions and negative ions is that the intensities of luminescence centers can reach the maxima at lower fluences under negative-ion irradiation due to free charge accumulation.
Performance Improvement of GaN-Based Violet Laser Diodes
De-Gang Zhao, De-Sheng Jiang, Ling-Cong Le, Jing Yang, Ping Chen, Zong-Shun Liu, Jian-Jun Zhu, Li-Qun Zhang
Chin. Phys. Lett.    2017, 34 (1): 017101.   DOI: 10.1088/0256-307X/34/1/017101
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The influences of InGaN/GaN multiple quantum wells (MQWs) and AlGaN electron-blocking layers (EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two different temperatures, the same-temperature growth of InGaN well and GaN barrier layers has a positive effect on the threshold current and slope efficiency of laser diodes, indicating that the quality of MQWs is improved. In addition, the performance of GaN laser diodes could be further improved by increasing Al content in the AlGaN EBL due to the fact that the electron leakage current could be reduced by properly increasing the barrier height of AlGaN EBL. The violet laser diode with a peak output power of 20 W is obtained.
Improved Polarization Retention of BiFeO$_{3}$ Thin Films Using GdScO$_{3}$ (110) Substrates
Shuai-Qi Xu, Yan Zhang, Hui-Zhen Guo, Wen-Ping Geng, Zi-Long Bai, An-Quan Jiang
Chin. Phys. Lett.    2017, 34 (2): 027701.   DOI: 10.1088/0256-307X/34/2/027701
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Epitaxial ferroelectric thin films on single-crystal substrates generally show a preferred domain orientation in one direction over the other in demonstration of a poor polarization retention. This behavior will affect their application in nonvolatile ferroelectric random access memories where bipolar polarization states are used to store the logic 0 and 1 data. Here the retention characteristics of BiFeO$_{3}$ thin films with SrRuO$_{3}$ bottom electrodes on both GdScO$_{3}$ (110) and SrTiO$_{3}$ (100) substrates are studied and compared, and the results of piezoresponse force microscopy provide a long time retention property of the films on two substrates. It is found that bismuth ferrite thin films grown on GdScO$_{3}$ substrates show no preferred domain variants in comparison with the preferred downward polarization orientation toward bottom electrodes on SrTiO$_{3}$ substrates. The retention test from a positive-up domain to a negative-down domain using a signal generator and an oscilloscope coincidentally shows bistable polarization states on the GdScO$_{3}$ substrate over a measuring time of 500 s, unlike the preferred domain orientation on SrTiO$_{3}$, where more than 65% of upward domains disappear after 1 s. In addition, different sizes of domains have been written and read by using the scanning tip of piezoresponse force microscopy, where the polarization can stabilize over one month. This study paves one route to improve the polarization retention property through the optimization of the lattice-mismatched stresses between films and substrates.
Intrinsic Features of an Ideal Glass
Deyan Sun, Cheng Shang, Zhipan Liu, Xingao Gong
Chin. Phys. Lett.    2017, 34 (2): 026402.   DOI: 10.1088/0256-307X/34/2/026402
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In order to understand the long-standing problem of the nature of glass states, we perform intensive simulations on the thermodynamic properties and potential energy surface of an ideal glass. It is found that the atoms of an ideal glass manifest cooperative diffusion, and show clearly different behavior from the liquid state. By determining the potential energy surface, we demonstrate that the glass state has a flat potential landscape, which is the critical intrinsic feature of ideal glasses. When this potential region is accessible through any thermal or kinetic process, the glass state can be formed and a glass transition will occur, regardless of any special structural character. With this picture, the glass transition can be interpreted by the emergence of configurational entropies, as a consequence of flat potential landscapes.
The 18.3% Silicon Solar Cells with Nano-Structured Surface and Rear Emitter
Jun-Na Zhang, Lei Wang, Zhun Dai, Xun Tang, You-Bo Liu, De-Ren Yang
Chin. Phys. Lett.    2017, 34 (2): 028801.   DOI: 10.1088/0256-307X/34/2/028801
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A nano-structured surface is formed on the pyramid structure of n-type silicon solar cells by size-controlled silver nano-particle assisted etching. Such a nano-structure creates a front average weighted reflectance of less than 2.5% in the 300–1200 nm range due to the broadband reflection suppression. The sodium hydroxide is used to obtain the low-area surface by post-etching the nano-structure, thus the severe carrier recombination associated with the nano-structured surface could be reduced. After emitter forming, screen printing and firing by means of the industrial fabrication protocol, an 18.3%-efficient nano-structured silicon solar cell with rear emitter is fabricated. The process of fabricating the solar cells matches well with industrial manufacture and shows promising prospects.
Ballistic Transport through a Strained Region on Monolayer Phosphorene
Yi Ren, Fang Cheng
Chin. Phys. Lett.    2017, 34 (2): 027302.   DOI: 10.1088/0256-307X/34/2/027302
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We investigate quantum transport of carriers through a strained region on monolayer phosphorene theoretically. The electron tunneling is forbidden when the incident angle exceeds a critical value. The critical angles for electrons tunneling through a strain region for different strengths and directions of the strains are different. Owing to the anisotropic effective masses, the conductance shows a strong anisotropic behavior. By tuning the Fermi energy and strain, the channels can be transited from opaque to transparent, which provides us with an efficient way to control the transport of monolayer phosphorene-based microstructures.