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Finite Volume Time Domain with the Green Function Method for Electromagnetic Scattering in Schwarzschild Spacetime
Shou-Qing Jia
Chin. Phys. Lett. 2019, 36 (1): 010401 .   DOI: 10.1088/0256-307X/36/1/010401
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The finite volume time domain (FVTD) algorithm and Green function algorithm are extended to Schwarzschild spacetime for numerical simulation of electromagnetic scattering. The FVTD method in Schwarzschild spacetime is developed by filling the flat spacetime with an equivalent medium. The Green function in Schwarzschild spacetime is acquired by solving initial value problems. Both the FVTD code and the Green function code are validated by numerical results. Scattering in Schwarzschild spacetime is simulated with these methods.
A New Probe: AFM Measurements for Random Disorder Systems
R. Salci, D. A. Acar, O. Oztirpan, M. Ramazanoglu
Chin. Phys. Lett. 2019, 36 (1): 010501 .   DOI: 10.1088/0256-307X/36/1/010501
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We study the quenched random disorder (QRD) effects created by aerosil dispersion in the octylcyanobiphenyl (8CB) liquid crystal (LC) using atomic force microscopy technique. Gelation process in the 8CB+aerosil gels yields a QRD network which also changes the surface topography. By increasing the aerosil concentration, the original smooth pattern of LC sample surfaces is suppressed by the emergence of a fractal aerosil surface effect and these surfaces become more porous, rougher and they have more and larger crevices. The dispersed aerosil also serves as pinning centers for the liquid crystal molecules. It is observed that via the diffusion-limited-aggregation process, aerosil nano-particles yield a fractal-like surface pattern for the less disordered samples. As the aerosil dispersion increases, the surface can be described by more aggregated regions, which also introduces more roughness. Using this fact, we show that there is a net correlation between the short-range ordered x-ray peak widths (the results of previous x-ray diffraction experiments) and the calculated surface roughness. In other words, we show that these QRD gels can also be characterized by their surface roughness values.
Analysis of Transition Mechanism of Cubic Boron Nitride Single Crystals under High Pressure-High Temperature with Valence Electron Structure Calculation
Mei-Zhe Lv, Bin Xu, Li-Chao Cai, Feng Jia, Xing-Dong Yuan
Chin. Phys. Lett. 2019, 36 (1): 013101 .   DOI: 10.1088/0256-307X/36/1/013101
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The possibilities of hexagonal boron nitride (hBN) and lithium boron nitride (Li$_{3}$BN$_{2}$) transition into cubic boron nitride (cBN) under synthetic pressure 5.0 GPa and synthetic temperature 1700 K are analyzed with the use of the empirical electron theory of solids and molecules. The relative differences in electron density are calculated for dozens of bi-phase interfaces hBN/cBN, Li$_{3}$BN$_{2}$/cBN. These relative differences of hBN/cBN are in good agreement with the first order of approximation ($ < $10%), while those of Li$_{3}$BN$_{2}$/cBN are much greater than 10%. This analysis suggests that Li$_{3}$BN$_{2}$ is impossible to be intermediate phase but is a catalyst and cBN should be directly transformed by hBN.
Localization and Steering of Light in One-Dimensional Parity-Time Symmetric Photonic Lattices
Xing Wei, ZhenDa Xie, Yan-Xiao Gong, Xinjie Lv, Gang Zhao, ShiNing Zhu
Chin. Phys. Lett. 2019, 36 (1): 014201 .   DOI: 10.1088/0256-307X/36/1/014201
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We theoretically study the propagation dynamics of input light in one-dimensional mixed linear-nonlinear photonic lattices with a complex parity-time symmetric potential. Numerical computation shows simultaneous localization and steering of the optical beam due to the asymmetric scatter and interplay between Kerr-type nonlinearity and PT symmetry. This may provide a feasible measure for manipulation light in optical communications, integrated optics and so on.
Dynamically Tunable Perfect Absorbers Utilizing Hexagonal Aluminum Nano-Disk Array Cooperated with Vanadium Dioxide
Peng Zhou, Gai-Ge Zheng, Yun-Yun Chen, Feng-Lin Xian, Lin-Hua Xu
Chin. Phys. Lett. 2019, 36 (1): 014202 .   DOI: 10.1088/0256-307X/36/1/014202
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A tunable perfect absorber composed of hexagonal-arranged aluminum nano-disk array embedded in the vanadium dioxide (VO$_{2}$) film is proposed. The aim is to achieve the tunability of resonance absorption peak in the visible and near-infrared regimes. Numerical results reveal that the absorption peak achieves a large tunability of 76.6% while VO$_{2}$ undergoes a structural transition from insulator phase to metallic phase. By optimizing the structural parameters, an average absorption of 95% is achieved from 1242 to 1815 nm at the metallic phase state. In addition, the near unity absorption can be fulfilled in a wide range of incident angle (0$^{\circ}$–60$^{\circ}$) and under all polarization conditions. The method and results presented here would be beneficial for the design of active optoelectronic devices.
Asymmetric and Single-Side Splitting of Dissipative Solitons in Complex Ginzburg–Landau Equations with an Asymmetric Wedge-Shaped Potential
Yun-Cheng Liao, Bin Liu, Juan Liu, Jia Chen
Chin. Phys. Lett. 2019, 36 (1): 014203 .   DOI: 10.1088/0256-307X/36/1/014203
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We report some novel dynamical phenomena of dissipative solitons supported by introducing an asymmetric wedge-shaped potential (just as a sharp 'razor') into the complex Ginzburg–Landau equation with the cubic-quintic nonlinearity. The potentials corresponding to a local refractive index modulation with breaking symmetry can be realized in an active optical medium with respective expanding antiwaveguiding structures. Using the razor potential acting on a central dissipative soliton, possible outcomes of asymmetric and single-side splitting of dissipative solitons are achieved with setting different strengths and steepness of the potentials. The results can potentially be used to design a multi-route splitter for light beams.
Localizing and Characterizing Colloidal Particles Scattering Using Lens-free Holographic Microscopy
Xia Hua, Cheng Yang, Ye Huang, Feng Yan, Xun Cao
Chin. Phys. Lett. 2019, 36 (1): 014204 .   DOI: 10.1088/0256-307X/36/1/014204
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Lens-free holographic microscopy could achieve both improved resolution and field of view (FOV), which has huge potential applications in biomedicine, fluid mechanics and soft matter physics. Unfortunately, due to the limited sensor pixel size, target objects could not be located to a satisfactory level. Recent studies have shown that electromagnetic scattering can be fitted to digital holograms to obtain the 3D positions of isolated colloidal spheres with nanometer precision and millisecond temporal resolution. Here, we describe a lens-free holographic imaging technique that fits multi-sphere superposition scattering to digital holograms to obtain in situ particle position and model parameters: size and refractive index of colloidal spheres. We show that the proposed method can be utilized to analyze the location and character of colloidal particles under large FOV with high density.
First-Stokes Wavelengths at 1175.8 and 1177.1nm Generated in a Diode End-Pumped Nd:YVO$_{4}$/LuVO$_{4}$ Raman Laser
Qing-Qing Zhou, Shen-Cheng Shi, Si-Meng Chen, Yan-Min Duan, Xi-Mei Zhang, Jing Guo, Bin Zhao, Hai-Yong Zhu
Chin. Phys. Lett. 2019, 36 (1): 014205 .   DOI: 10.1088/0256-307X/36/1/014205
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A diode end-pumped acousto-optic Q-switched Nd:YVO$_{4}$/LuVO$_{4}$ Raman laser is demonstrated. Both YVO$_{4}$ and LuVO$_{4}$ can work as Raman gain, and slightly different active vibration modes of both crystals can result in different first-Stokes wavelengths. The output characteristic as the Raman competition between YVO$_{4}$ and LuVO$_{4}$ crystals for the laser systems with both shared cavity and coupled cavity is experimentally investigated. For the shared cavity, simultaneous Raman conversion in both YVO$_{4}$ and LuVO$_{4}$ crystals is achieved with dual-wavelength emission at 1175.8 and 1177.1 nm. The maximum output power of 1.03 W and the conversion efficiency of 10.3% are obtained. The 0.84 W single first Stokes wavelength at 1177.1 nm with LuVO$_{4}$ Raman conversion is achieved with the coupled cavity. The results show that the coupled cavity with short Raman cavity can obtain a narrow pulse width. The separated laser crystal and Raman gain media with different vanadates in shared cavity have advantages in achieving dual-wavelength lasers with small frequency intervals.
Unsteady Liquid Film Flow with a Prescribed Free-Surface Velocity
Tiegang Fang, Fujun Wang
Chin. Phys. Lett. 2019, 36 (1): 014701 .   DOI: 10.1088/0256-307X/36/1/014701
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A liquid film flow over a flat plate is investigated by prescribing the unsteady interface velocity. With this prescribed surface velocity, the governing Navier–Stokes (NS) equations are transformed into a similarity ordinary differential equation, which is solved numerically. The flow characteristics is controlled by an unsteadiness parameter $S$ and the flow direction parameter ${\it \Lambda}$. The results show that solutions only exist for a certain range of the unsteadiness parameter, i.e., $S\leqslant 1$ for ${\it \Lambda} =-1$ and $S\leqslant -2.815877$ for ${\it \Lambda} =1$. In the solution domain, the dimensionless liquid film thickness $\beta $ decreases with $S$ for both the cases. The wall shear stress increases with the decrease of $S$ for ${\it \Lambda} =-1$. However, for ${\it \Lambda} =-1$ the shear stress magnitude first decreases and then increases with the decrease of $S$. There are no zero crossing points for the velocity profiles for both the cases. The profiles of velocity stay either positive or negative all the time, except for the wall zero velocity. Consequently, the vertical velocity becomes a monotonic function. To maintain the prescribed velocity, mass transpiration is generally needed, but for the shrinking film case it is possible to have an impermeable wall. The results are also an exact solution to the full NS equations.
Electron Magnetohydrodynamics Magnetic Reconnection Experiment on Keda Linear Magnetized Plasma Device
Feibin Fan, Jinlin Xie, Qiaofeng Zhang, Longlong Sang, Weixing Ding
Chin. Phys. Lett. 2019, 36 (1): 015201 .   DOI: 10.1088/0256-307X/36/1/015201
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We conduct an electron magnetohydrodynamics magnetic reconnection experiment with guide-field in our Keda linear magnetized plasma device, in which two pulsed currents with the same direction are conducted in parallel with the axial direction of the main chamber of the device using two long aluminum sticks. After approximately 5 μs, an X-type magnetic field line topology is formed at the center of the chamber. With the formation of the X-type topology of magnetic field lines, we can also find the rapid increase of the current and ratio of the common flux to the private flux in this area. Additionally, a reduction in the plasma density and the plasma density concentration along one pair of separatrices can also be found.
Instability of Epitaxially Strained Thin Films Based on Nonlocal Elasticity
Wang-Min Zhou, Wang-Jun Li
Chin. Phys. Lett. 2019, 36 (1): 016801 .   DOI: 10.1088/0256-307X/36/1/016801
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We perform a linear analysis of the elastic fields and stability of epitaxially strained thin films based on nonlocal elasticity. We derive expressions of perturbed stresses to the first order of perturbation amplitude, which show that the stresses are directly proportional to the lattice mismatch and the perturbation amplitude, and decrease with an increase in the perturbation wavelength. The critical perturbation wavelength distinguishes whether the flat film for the perturbation is stable, which is inversely proportional to the square of the mismatch and decreases with the thickness of the film.
Spin Caloritronic Transport of Tree-Saw Graphene Nanoribbons
Yu-Zhuo LV, Peng ZHAO
Chin. Phys. Lett. 2019, 36 (1): 017301 .   DOI: 10.1088/0256-307X/36/1/017301
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Using density functional theory combined with non-equilibrium Green's function method, we investigate the spin caloritronic transport properties of tree-saw graphene nanoribbons. These systems have stable ferromagnetic ground states with a high Curie temperature that is far above room temperature and exhibit obvious spin-Seebeck effect. Moreover, thermal colossal magnetoresistance up to 10$^{20}$% can be achieved by the external magnetic field modulation. The underlying mechanism is analyzed by spin-resolved transmission spectra, current spectra and band structures.
High-Quality InSb Grown on Semi-Insulting GaAs Substrates by Metalorganic Chemical Vapor Deposition for Hall Sensor Application
Xin Li, Yu Zhao, Min Xiong, Qi-Hua Wu, Yan Teng, Xiu-Jun Hao, Yong Huang, Shuang-Yuan Hu, Xin Zhu
Chin. Phys. Lett. 2019, 36 (1): 017302 .   DOI: 10.1088/0256-307X/36/1/017302
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High-quality InSb epilayers are grown on semi-insulting GaAs substrates by metalorganic chemical vapor deposition using an indium pre-deposition technique. The influence of V/III ratio and indium pre-deposition time on the surface morphology, crystalline quality and electrical properties of the InSb epilayer is systematically investigated using Nomarski microscopy, atomic force microscopy, high-resolution x-ray diffraction, Hall measurement and contactless sheet resistance measurement. It is found that a 2-μm-thick InSb epilayer grown at 450$^{\circ}\!$C with a V/III ratio of 5 and an indium pre-deposition time of 2.5 s exhibits the optimum material quality, with a root-mean-square surface roughness of only 1.2 nm, an XRD rocking curve with full width at half maximum of 358 arcsec and a room-temperature electron mobility of $4.6\times10^{4}$ cm$^{2}$/V$\cdot$s. These values are comparable with those grown by molecular beam epitaxy. Hall sensors are fabricated utilizing a 600-nm-thick InSb epilayer. The output Hall voltages of these sensors exceed 10 mV with the input voltage of 1 V at 9.3 mT and the electron mobility of $3.2\times10^{4}$ cm$^{2}$/V$\cdot$s is determined, which indicates a strong potential for Hall applications.
Direct Microwave Synthesis of 11-Type Fe(Te,Se) Polycrystalline Superconductors with Enhanced Critical Current Density
Bo-Jin Pan, Kang Zhao, Tong Liu, Bin-Bin Ruan, Shuai Zhang, Gen-Fu Chen, Zhi-An Ren
Chin. Phys. Lett. 2019, 36 (1): 017401 .   DOI: 10.1088/0256-307X/36/1/017401
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We report a direct microwave synthesis method for the preparation of 11-type high quality Fe(Te,Se) polycrystalline superconductors. The bulk samples are rapidly synthesized under the microwave irradiation during several minutes, with a subsequent annealing process at 400$^{\circ}\!$C. The samples exhibit a nearly single phase of the tetragonal PbO-type crystal structure with minor impurities. Morphology characterization shows high density, tight grain connectivity and large grain sizes around 100 μm with small cavities inside the sample. Resistivity and magnetization measurements both show similar superconducting transitions above 14 K. The magnetic hysteresis measurements display broad and symmetric loops without magnetic background, and a high critical current density $J_{\rm c}$ about $1.2\times10^{4}$ A/cm$^{2}$ at 2 K and 7 T is estimated by the Bean model. Compared with the solid-state reaction synthesized samples, these superconducting bulks from microwave-assisted synthesis are possibly free of the interstitial Fe due to smaller $c$-axis, higher $T_{\rm c}$ in magnetic transitions, better $M$–$H$ loops without magnetic background and greatly enhanced $J_{\rm c}$, and are promising as raw materials for the non-toxic Fe-based superconducting wires for large currents and high field applications.
Disappearance of Superconductivity and a Concomitant Lifshitz Transition in Heavily Overdoped Bi$_2$Sr$_2$CuO$_{6}$ Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy
Ying Ding, Lin Zhao, Hong-Tao Yan, Qiang Gao, Jing Liu, Cheng Hu, Jian-Wei Huang, Cong Li, Yu Xu, Yong-Qing Cai, Hong-Tao Rong, Ding-Song Wu, Chun-Yao Song, Hua-Xue Zhou, Xiao-Li Dong, Guo-Dong Liu, Qing-Yan Wang, Shen-Jin Zhang, Zhi-Min Wang, Feng-Feng Zhang, Feng Yang, Qin-Jun Peng, Zu-Yan Xu, Chuang-Tian Chen, X. J. Zhou
Chin. Phys. Lett. 2019, 36 (1): 017402 .   DOI: 10.1088/0256-307X/36/1/017402
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By partially doping Pb to effectively suppress the superstructure in single-layered cuprate Bi$_2$Sr$_2$CuO$_{6+\delta}$ (Pb-Bi2201) and annealing them in vacuum or in high pressure oxygen atmosphere, a series of high quality Pb-Bi2201 single crystals are obtained with $T_{\rm c}$ covering from 17 K to non-superconducting in the overdoped region. High resolution angle resolved photoemission spectroscopy measurements are carried out on these samples to investigate the evolution of the Fermi surface topology with doping in the normal state. Clear and complete Fermi surfaces are observed and quantitatively analyzed in all of these overdoped Pb-Bi2201 samples. A Lifshitz transition from hole-like Fermi surface to electron-like Fermi surface with increasing doping is observed at a doping level of $\sim$0.35. This transition coincides with the change that the sample undergoes superconducting-to-non-superconducting states. Our results reveal the emergence of an electron-like Fermi surface and the existence of a Lifshitz transition in heavily overdoped Bi2201 samples. This provides important information in understanding the connection between the disappearance of superconductivity and the Lifshitz transition in the overdoped region.
Epitaxial Growth and Magnetic Properties of NiMnAs Films on GaAs Substrates
Jia-Lin Ma, Hai-Long Wang, Xing-Min Zhang, Shuai Yan, Wen-Sheng Yan, Jian-Hua Zhao
Chin. Phys. Lett. 2019, 36 (1): 017501 .   DOI: 10.1088/0256-307X/36/1/017501
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Single-phase Ni$_{0.92}$Mn$_{1.08}$As films with strained $C_{\rm 1b}$ symmetry are grown on GaAs (001) substrates. In addition, a preferred epitaxial configuration of (110)-orientated Ni$_{0.92}$Mn$_{1.08}$As on (001)-orientated GaAs is revealed by synchrotron radiation measurement. The magnetic properties of the films are found to be significantly influenced by the growth temperature and the optimized growth temperature is determined to be $\sim$$370^\circ\!$C. According to the results of x-ray absorption spectroscopy, these phenomena can be attributed to the variation of the local electronic structure of the Mn atoms. Our work provides useful information for the further investigations of NiMnAs, which is a theoretically predicted half-metal.
From Claringbullite to a New Spin Liquid Candidate Cu$_3$Zn(OH)$_6$FCl
Zili Feng, Wei Yi, Kejia Zhu, Yuan Wei, Shanshan Miao, Jie Ma, Jianlin Luo, Shiliang Li, Zi Yang Meng, Youguo Shi
Chin. Phys. Lett. 2019, 36 (1): 017502 .   DOI: 10.1088/0256-307X/36/1/017502
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The search for quantum spin liquid (QSL) materials has attracted significant attention in the field of condensed matter physics in recent years, however so far only a handful of them are considered as candidates hosting QSL ground state. Owning to their geometrically frustrated structures, Kagome materials are ideal systems to realize QSL. We synthesize the kagome structured material claringbullite (Cu$_4$(OH)$_6$FCl) and then replace inter-layer Cu with Zn to form Cu$_3$Zn(OH)$_6$FCl. Comprehensive measurements reveal that doping Zn$^{2+}$ ions transforms magnetically ordered Cu$_4$(OH)$_6$FCl into a non-magnetic QSL candidate Cu$_3$Zn(OH)$_6$FCl. Therefore, the successful syntheses of Cu$_4$(OH)$_6$FCl and Cu$_3$Zn(OH)$_6$FCl provide not only a new platform for the study of QSL but also a novel pathway of investigating the transition between QSL and magnetically ordered systems.
A Novel Method for PIT Effects Based on Plasmonic Decoupling
Bin Sun, Fei-Feng Xie, Shuai Kang, You-chang Yang, Jian-Qiang Liu
Chin. Phys. Lett. 2019, 36 (1): 017801 .   DOI: 10.1088/0256-307X/36/1/017801
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A tunable dual-band stop-band THz spectrum can be realized in a hybrid structure, which consists of metal nanoribbon arrays clad by graphene nanoribbons. Dual-band spectra can be controlled separately by the nanoribbon width $w$ and graphene chemical potential $\mu_{\rm c}$. We explain that two local plasmonic modes excited at graphene ribbons belong to different gratings, which uncouple with each other by electro-magnetic shielding of the metal ribbons. Furthermore, plasmonic induced transparent (PIT) effects can also be realized by making the two transmission notches close to each other, with better performance than the PIT system based on plasmonic coupling, such as with a larger extinction radio and a tunable transparency window.
18 articles