bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of vortex beams by the four-step phase plates
Authors: Shi Jian-Zhen  , Yang Shen  , Zou Ya-Qi  , Ji Xian-Ming  , Yin Jian-Ping  ,   Science College, Nantong University, Nantong 226019, China;,   State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062, China
Published: December 2020

The generation and application of the vortex beams are part of the hot topics in the optical field. In this paper, the phase structure of the four-step phase plates, analyzed by Fourier series expansion method, is composed of a series of spiral phase plates. When the phase plate is directly irradiated by linearly polarized light, multi-order diffraction waves with different topological charge numbers are generated. Unlike vortex waves, the intensity distribution of the multi-order diffraction has a deviation from the axial symmetry due to the interference with each other. On this basis, a new scheme is proposed to generate vortex beams by the four-step phase plates. With the help of Mach-Zehnder interferometer, the diffraction waves generated by two pieces of the four-step phase plates overlap each other. By adjusting the phase difference of the Mach-Zehnder interferometer, some orders of diffraction waves generate destructive interference while the others generate constructive interference. Thus the linear polarized light can be converted into vortex beams. The diffraction intensity and angular momentum distributions of the four-step phase plates with different cycle numbers are numerically simulated and compared with the spiral phase plates, we can provethat the vortex beams can be obtained by simple four-step phase plates which are the same as those obtained by spiral phase plates. In addition, the four-step phase plates with a small cycle number can generate vortex beams with a large topological charge number and the fabrication difficulty of the phase plates is reduced.
Analysis on reconstruction of virtual images of Fourier telescopy
Authors: Yu Shu-Hai  , Dong Lei  , Liu Xin-Yue  , Ling Jian-Yong  ,   Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
Published: December 2020

Fourier telescopy can realize high resolution imaging to remote, small and dim target by using laser as the light source. The signal-to-noise ratio of imaging system is easy to improve by increasing the area of receiver. However, numerical simulation shows that the reconstruction images sometimes has a virtual phenomenon. It reduces the quality of reconstruction images, and even cannot have a resolution to the imaging target. Based on Fourier telescopy imaging principle, using T type transmitting array, the reason of forming virtual images is indicated by mathematical deduction. The spatial frequency error between the actual getting and setting would be produced when the laser beams scan the x or y axis with pitch error. The error would cause the random phase influence when calculating the single Fourier frequency of target by using phase closure on the axis and quadrant scan. Using integrated spatial frequency of transmitter array to reconstruct the image of target would cause a virtual phenomenon. By contrasting reconstruction images it is found that the image quality is reduced seriously, even the virtual phenomenon appears when the transmitting system is axially scanned with pitch error, and it decreases slightly on quadrant scan. In the present paper, we consider the reason of the phase closure of quadrant of T type transmitting array relies on axial frequency. At the same pitch error, different scan methods would cause different reconstruction images. The directions of virtual images are the same within the axial error. The computer simulation confirms the validity of the above analysis by three different modes of transmitter array through using the next field experiment parameters.
High sensitive measurement of optical rotation based on photo-elastic modulation
Authors: Li Ke-Wu  , Wang Zhi-Bin  , Chen You-Hua  , Yang Chang-Qing  , Zhang Rui  ,   Key Laboratory of Electronic Measurement Technology, North University of China, Taiyuan 030051, China;,   Engineering and Technology Research Center of Shanxi Provincial for Optical-Electric Information and Instrument, Taiyuan 030051, China;,   School of Information and Communication Engineering, North University of China, Taiyuan 030051, China
Published: December 2020

In order to realize the continuous and stable, high speed, high precise and high sensitive measurement of optical rotation, and considering the application advantages of photo-elastic polarization modulation technology with high modulation frequency, high modulation purity, high modulation accuracy and good modulation stability, a new scheme about the measurement of optical rotation based on photo-elastic modulation is presented. Probe laser orderly passes through a polarizer, the rotation sample to be measured, a photo-elastic modulator, and a analyzer, and finally reaches the detector, this system uses less optical devices than any others previously reported, so it considerably reduces the measurement error that may be introduced by the optical devices. In the detecting of light path, the polarization axes of the polarizer and analyzer are respectively adjusted with respect to the photo-elastic modulator's fast axis directions 0° and 45°, the optical arrangements make the rotation angle to be measured appear in the alternating current signal, and the photo-elastic modulator's residual birefringence only appears in the odd harmonics. Consequently, the second harmonic signal of photo-elastic modulation is selected as the object to study, which effectively avoids the influence of residual birefringence of the photo-elastic modulator on optical rotation measurement, and efficiently improves the accuracy of optical rotation measurement. What is more, the detector output signal is separated into two parts, the direct current and alternating current signal. The alternating current signal is amplified, then outputs by a lock-in amplifier, which enhances the measurement sensitivity further. A ingenious verification test experiment is done, firstly, the probe laser is modulated into circularly polarized light, and then precisely rotates the polarizer to replace the optical rotation sample. The results show that the new scheme is feasible, this experiment gives the proportion coefficient of the measurement system, the sensitivity of optical rotation measurement increasing up to 3.15× 10-7 rad, and the measurement precision exceeding 0.3%. Therefore, in this scheme achieved is a high sensitive and precise measurement of optical rotation, and it is expected to be applied to the high sensitive and precise rotation measurement. The verification test experiment designed by us can also provide a outstanding calibration reference for high sensitive rotation measurement system.
Generation and application of two-photon Raman laser for manipulation of internal state of Cs atom
Authors: Wang Zhi-Hui  , Tian Ya-Li  , Li Gang  , Zhang Tian-Cai  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Two-photon Raman process (TPRP) is an important technique in controlling the atomic internal states. It plays an important role in quantum manipulation and quantum information process. A reliable Raman laser for specific atom is the first step to demonstrate TPRP and quantum manipulation of an atom. In this paper, we theoretically analyze the two-photon Raman process regarding to Cesium “clock states” |6S1/2, F=4, mF=0 and |6S1/2, F=3, mF=0, and we obtain the dependences of the corresponding Rabi frequency on one-and two-photon detunings and one-photon Rabi frequencies in a realistic multi-level Cesium atom system. We find that to obtain an atom state flopping efficiency of 0.99 the Raman laser power fluctuation should be controlled to be smaller than 3.2%. We also report our simple experimental Raman laser system for TPRP of Cesium atom based on a fiber waveguide phase modulator. The phase modulator is driven by a 4.6 GHz microwave source and the two first-order sidebands with a frequency difference of 9.19 GHz are filtered out by a Fabry-Pérot cavity with a finesse of 48. After an amplitude-modulator-based intensity stabilization system, a total power of 73 μupW with a fluctuation of 2.2% within 90 min is obtained. By applying this Raman laser to a single Cesium atom trapped in a micrometer size far-off resonant trap (FORT), we obtain Raman spectra between Cesium “clock states” |6S1/2, F=4, mF=0 and |6S1/2, F=3, mF=0. The discrepancy between the two-photon resonance frequency and the defined clock frequency 9.192631770 GHz is due to the differential Stark shifts by FORT beam and Raman beams as well as the inaccuracy of the microwave source. By varying the Raman pulse length we also show the corresponding Rabi flopping with a rate of 153 kHz, which is consistent with the theoretical calculation. The obtained state transfer efficiency of 0.75 is much smaller than theoretical expectation 0.99, which is mainly limited by the state initialization efficiency. The Raman laser system reported in this paper is simple and reliable to realize and it provides a reliable method to manipulate the Cesium internal state. Moreover it could also be easily extended to other system for quantum manipulation of other species of atom.
Amplifier similariton oscillator using 10 m photonic crystal fiber
Authors: Shi Jun-Kai  , Chai Lu  , Zhao Xiao-Wei  , Liu Bo-Wen  , Hu Ming-Lie  , Li Yan-Feng  , Wang Qing-Yue  ,   Ultrafast Laser Laboratory, Key Laboratory of Optoelectronics Information Technique, Ministry of Education, School of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Ultrashort pulse laser with a repetition rate of below 10 MHz is suitable for a variety of micromachining applications to avoid plasma shielding effects. Besides, the parabolic pulse possesses clean wings, short pulse duration, and large peak power because only the linear chirp is accumulated during the propagation. Based on these two points, a similariton oscillator with a repetition rate of below 10 MHz is a most perfect seed source of an amplification system for micromachining. In this paper, an amplifier similariton oscillator with dispersion map based on a piece of 10 m Yb-doped large-mode-area single-polarization photonic crystal fiber is demonstrated. The semiconductor saturable absorber mirror is employed in the linear cavity as an end mirror to initiate and maintain the mode-locking operation. An adjustable slit is adopted between the end mirror and grating pair in another arm, as a central wavelength adjuster and the spectral filter to ensure the laser operational wavelength in accordance with the working wavelength of semiconductor saturable absorber mirror and the stability of mode-locking operation. The stable single-pulse mode-locking operation can be achieved by adjusting the intracavity dispersion and the operating wavelength. With the net cavity dispersion of-0.89 ps2, a spectrum with steep and smooth edges is obtained, which means that the laser does not operate in the soliton regime but in the dispersion-mapped amplifier similariton regime. A highest output power of 820 mW is obtained with a pulse duration of 6.2 ps and spectral width of 3.84 nm under a pump power of 12.8 W. The repetition rate is 8.6 MHz, corresponding to a pulse energy of 95 nJ. It is the first time that the similariton with a repetition rate of lower than 10 MHz and a highest pulse energy of 95 nJ from a similariton laser has been achieved, to the best of our knowledge. Numerical simulation results confirm that the self-similar evolution is achieved in the gain fiber, and the parabolic-and gauss-shaped pulse can be emitted at the zero-order reflection of the grating and after the slit, respectively.
Modal expansion analysis of nonlinear circumferential guided wave propagation in a circular tube
Authors: Gao Guang-Jian  , Deng Ming-Xi  , Li Ming-Liang  ,   Logistics Engineering University, Chongqing 401331, China
Published: December 2020

Within the second-order perturbation approximation, the nonlinear effect of primary circumferential guided wave propagation in a circular tube is investigated using modal expansion analysis for waveguide excitation. The nonlinearity of the wave equation governing the wave propagation ensures the second-harmonic generation accompanying primary circumferential guided wave propagation. This nonlinearity may be treated as a second-order perturbation of the linear elastic response. The fields of the second harmonics of primary circumferential guided wave propagation are considered as superpositions of the fields of a series of double frequency circumferential guided wave (DFCGW) modes. Based on the momentum theorem and mathematical formulae of nonlinear stress tensor and its divergence under the cylindrical coordinate system, the mathematical expressions of the corresponding double frequency traction stress tensors and bulk driving forces are deduced for a certain primary circumferential guided wave mode. Subsequently, the equation governing the DFCGW mode expansion coefficient is established. Finally, the mathematical expression of second-harmonic field of the primary circumferential guided wave mode in a tube is derived. The results of the theoretical analyses and numerical calculations indicate that the degree of cumulative growth of the DFCGW mode with circumferential angle is obviously influenced by that of phase velocity matching between the primary and double frequency wave modes. It is found that the amplitude of the DFCGW mode can grow with circumferential angle when its phase velocity matches with that of the primary circumferential guided wave, and that the amplitude of the DFCGW mode will show a beat effect with circumferential angle when its phase velocity is not equal to that of the primary wave mode. The DFCGW mode, whose phase velocity matches with that of the primary wave mode, plays a dominant role in the field of second harmonic generated by the primary wave mode propagation, and the contribution of the other DFCGW modes to the said second-harmonic field is negligible after the primary wave mode has propagated some circumferential angle.
Dynamic process and flow-rate regulation mechanism of particle inertial focusing in an asymmetric ally curved microchannel
Authors: Tang Wen-Lai  , Xiang Nan  , Zhang Xin-Jie  , Huang Di  , Ni Zhong-Hua  ,   School of Mechanical Engineering, Southeast University, Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Nanjing 211189, China
Published: December 2020

In this paper, an asymmetrically curved microchannel device is designed and fabricated to quantitatively characterize the dynamic inertial focusing process of polystyrene particles and blood cells flowing along the channel. The experimental investigations are systematically carried out to probe into the regulation mechanisms of flow rate and particle size. Specifically, based on the particle fluorescent streak images and the corresponding intensity profiles at specific downstream positions, the lateral migration behaviors of particles in the mirochannel can be divided into two stages: the formation of focused streak and the shift of focusing position. It is also found that the channel structures with small radii are dominant during the whole inertial focusing process. A three-stage model is then presented to elucidate the flow-rate regulation mechanism in terms of the competition between inertial lift force and Dean drag force, according to the evolution of particle focusing dynamics with increasing flow rates. By making comparisons of focusing position and focusing ratio between two different-sized particles under various experimental conditions, we find that the larger particles have better focusing performances and stabilities, and the relative focusing position of different-sized particles can be adjusted by changing the driving flow rate. Finally, the applicability of the explored inertial focusing mechanisms for manipulating biological particles with complex features is investigated by analyzing the lateral migration behaviors of blood cells in the asymmetrically curved microchannel. The obtained conclusions are very important for understanding the particle focusing dynamics in micro-scale flows and developing the point-of-care diagnostic instruments.
Atomic and electronic structures of silicene and germanene on GaAs(111)
Authors: Zhang Xian  , Guo Zhi-Xin  , Cao Jue-Xian  , Xiao Si-Guo  , Ding Jian-Wen  ,   Department of Physics and Optoelectronics Institute for Nanophysics and Rare-Earth Luminescence, Hunan Key Laboratory of Micro-Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, China
Published: December 2020

By using first-principles method in the density-functional theory, we clarify the atomic and electronic structures of silicene and germanene on 1×1 GaAs(111). We find stable structures for silicene and germanene on both the As-terminated and Ga-terminated GaAs surfaces. The structures of silicene and germanene are similar to those of the free-standing ones, which present a honeycomb-hexagonal geometry. The cohesive energies of silicene and germanene on both As and Ga sides of GaAs surfaces are comparable to those of their bulk structures and/or those on Ag(111) substrates which have been widely observed in experiment, showing the possibility of synthesizing them on both sides of GaAs surfaces in experiment. The corresponding binding energies are in a range of 0.56-1.37 eV per Si (Ge) atom, 10 times larger than the usual van der Waals interaction, showing the covalent interaction between silicene (germanene) and GaAs surfaces. The band structure calculations show that such a covalent interaction induces the absence of Dirac electrons for silicene and germanene on GaAs surfaces. We then explore the method of recovering the Dirac electrons by using hydrogen (H) intercalation. It is found that the intercalated H atoms are chemically bonded to GaAs surface, and the silicene (germanene) shifts upward distance from GaAs surface increasing from 2.50-2.58 Å to 3.49-3.86 Å, where a covalent van-der-Waals interaction transition happens between silicene (germanene) and GaAs surface. Moreover, the distances between silicene (germanene) and H atoms are 30% and 8% larger than the atomic-radius sum of Si (Ge) and H on As-terminated and Ga-terminated GaAs surfaces, respectively. This shows that the interaction between silicene (germanene) and H on the As-terminated GaAs surface is obviously weaker than the typical covalent interaction, while on the Ga-terminated GaAs surface, it is comparable to the typical covalent interaction. This difference is induced by the difference in electronegativity between As and Ga atoms. We further find that the H intercalation recovers the Dirac electrons well on the As-terminated GaAs(111) due to the weaker Si (Ge)-H interaction, while it does not on the Ga-terminated GaAs(111) due to the stronger Si (Ge)-H interaction. The results are confirmed by performing calculations for silicene (germanene) on larger GaAs(111) surfaces, i.e., the 3×3 GaAs surface. Our study provides the theoretical basis for the preparation and application of silicene and germanene on semiconductor surfaces.
Properties of excited state of polaron in quantum disk in finite depth parabolic potential well
Authors: Zhao Cui-Lan  , Wang Li-Li  , Zhao Li-Li  ,   College of Physics and Electronic Information, Inner Mongolia University for Nationalities, Tongliao 028043, China;,   College of Computer and information Engineering, Chifeng University, Chifeng 024000, China
Published: December 2020

Studies of single quantum state measurement and the relevant physics are very important for the fields of quantum information and quantum coupution. In recent years, quantum dots as information carrier have become a hotpoint of research. The study on quantum dot properties has atracted a lot of attetion and made a series of progress.#br#In this paper, we formulate a theoretical method that can be used to investigate polaron properties in low-dimensional structures in finite depth potential well. We assume that an electron in a quantum disk which is in other medium is in parabolic potential field, but the effect of the medium on the electron in quantum disk is equivalent to a potential barrier with height V1 and width d. By expanding the finite height potential barrier as plane waves and Lee-Low-Pines unitary transformation for Hamiltonian, as well as variation for expectation value of Hamiltonian where trial wave functions are obtained by solving the energy eigen-value equation, the ground state energy, the first excited state energy, and excitation energy of polaron are drived.#br#Numerical calculation by using polaron unit, numerical results indicate that the first excited state energy and excitation energy of polaron increase with increasing the width or height of the potential barrier, because the probability of electron penetrating potential barrier will decrease as the width or height of potential barrier increases, so that electronic energy, the first excited state energy and excitation energy of polaron all increase. Numerical results also show that energies mentioned earlier decrease with increasing radius of quantum disk, which illustrates that the quantum disk has obvious quantum size effect.#br#It is also found from numerical results that the first excited state energy of polaron decreases with increasing effective confine length, it falls quickly when effective confine length is less than 0.3 and is a little change when effective confine length is more than 0.3. The longer the effective confine length, the more weakly the electron is bounded and the smaller the potential energy is, so that the first excited state energy of polaron decreases. Oppositely, the excitation energy of polaron increases with increasing effective confine length, because the first excited state energy decreases more slowly than the ground state energy.
Quantum thermal transport and spin thermoelectrics in low-dimensional nano systems: application of nonequilibrium Green's function method
Authors: Chen Xiao-Bin  , Duan Wen-Hui  ,   Department of Physics, Tsinghua University, Beijing 100084, China
Published: December 2020

Emerging novel properties of nanomaterials have been attracting attention. Besides quantum electronic transport properties, the breakdown of classical Fourier’s law and other significant quantum thermal behaviors such as quantized thermal conductance, phonon subbands, size effects, the bottleneck effect, and even interaction between heat and spin degrees of freedom have also been revealed over the past two decades. These phenomena can be well captured by the nonequilibrium Green’s function (NEGF) method, which is pretty simple under ballistic or quasi-ballistic regimes. In this review, we mainly focus on two aspects: quantum phonon transport and thermal-spin transport in low-dimensional nanostructures. First, we present a brief history of researches on thermal transport in nanostructures, summarize basic characteristics of quantum thermal transport, and then describe the basic algorithm and framework of the phonon NEGF method. Compared with other methods, the NEGF method facilitates numerical calculations and can systematically incorporate quantum many-body effects. We further demonstrate the power of phonon NEGF method by recent research progress: from the phonon NEGF method, distinct behaviors of phonon transport compared with those of electrons, intrinsic anisotropy of phonon transport, radial strain within elastic regime as quantum perturbation, two kinds of interfacial transport behaviors, defect-induced localization of local phonon density of states, unobservable phonon localization, etc, have been discovered in some particular low-dimensional nanomaterials or nanostructures. Second, the new concept of “spin caloritronics”, which is devoted to the study of thermally induced spin-related transport in magnetic systems and offers a brand-new way to realize thermal-spin or thermoelectric energy conversion, is also introduced. After concisely discussing the spin Seebeck effect, spin-dependent Seebeck effect, and magneto-Seebeck effect, we present the linear response theory with spin degree of freedom and show that by combining with linear response theory, NEGF method is also applicable for studying spin caloritronics, especially spin thermoelectrics. Finally, recent research on quantum dot models or numerical calculation of real materials give hints to the searching for high-ZT materials. With the ever-increasing demand for energy and increasing power density in highly integrated circuits, quantum thermal transport properties are not only of fundamental interest, but also crucial for future developing electronic devices. Relevant researches also pave the way to spin thermoelectrics, which has vast potential in thermoelectric spintronic devices and energy harvesting.
First-principles study of electronic structures and phase stabilities of ternary intermetallic compounds in the Mg-Y-Zn alloys
Authors: Ma Zhen-Ning  , Jiang Min  , Wang Lei  ,   Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China;,   College of Science, Shenyang Jianzhu University, Shenyang 110168, China
Published: December 2020

In the paper, the first-principles pseudopotential plane-wave method based on density functional theory is used to investigate the crystal structures, enthalpies of formation and electronic structures of X-Mg12YZn phase and W-Mg3Y2Zn3 phase in Mg-Y-Zn alloys. The obtained lattice constants of two phases are in good agreement with the available experimental values, which can reasonably reflect the accuracy of theoretical calculation. The calculated enthalpies of formation indicate that the W-Mg3Y2Zn3 and X-Mg12YZn phases have negative enthalpies of formation, which are-0.2787 eV/atom and-0.0268 eV/atom respectively. Both phases can form stable structures relative to single crystals Mg, Y and Zn, and the enthalpy of formation of W-Mg3Y2Zn3 phase is lower than that of X-Mg12YZn phase. The results for density of states show that the bonding of W-Mg3Y2Zn3 phase occurs mainly among the valence electrons of Mg 2p, Zn 3p and Y 4d orbits, the bonding peaks between-2.53 and 0 eV are derived from the hybridization of Mg 2p, Zn 3p and Y 4d orbits, the peaks between 5.07 and 7.51 eV predominantly originate from the hybridization of Mg 2p and Y 4d orbits. However, the bonding of X-Mg12YZn phase is mainly among the valence electrons of Mg 3s, Mg 2p, Zn 3p and Y 4d orbits. The bonding peaks between-2.30 and 0 eV originate mainly from 2p, 3p, and 4d orbit hybridization of Mg, Zn and Y, the peaks between 0 and 2.08 eV originate from the hybridization of Mg 3s, Mg 2p, Zn 3p and Y 4d orbits. At the same time, there is a pseudo-gap near each Fermi level of W-Mg3Y2Zn3 and X-Mg12YZn phases, which implies the presence of covalent bonding in the two phases. In addition, the charge densities respectively on (011) plane of W-Mg3Y2Zn3 phase and (0001) plane of X-Mg12YZn phase are analyzed, and the results indicate that the Zn-Y band exhibits covalent features in W-Mg3Y2Zn3 phase and X-Mg12YZn phase, the covalent bonding of W-Mg3Y2Zn3 phase is stronger than that of X-Mg12YZn phase. Compared with X-Mg12YZn phase, W-Mg3Y2Zn3 phase has a good phase stability attributed to its more bonding electron numbers in a low-energy region of the Fermi level.
Recent progress in Rashba spin orbit coupling on metal surface
Authors: Gong Shi-Jing  , Duan Chun-Gang  ,   Key Laboratory of Polar Materials and Devices, Ministry of Education, School of Information Science Technology, East China Normal University, Shanghai 200241, China
Published: December 2020

Spin-orbit coupling (SOC) is a bridge between the spin and orbital of an electron. Through SOC, spin of the electron can possibly be controlled throuth external electric fields. It is found that many novel physical phenomena in solids are related with SOC, for example, the magnetic anisotropy of magnetic materials, the spin Hall effect, and the topological insulator, etc. In the surface of solid or at the interface of heterostructure, Rashba SOC is induced by the structure inversion asymmetry. It was observed first in semiconductor heterostructure, which has an inversion asymmetric potential at the interface. Because Rashba SOC at the interface can be easily controlled through gate voltage, it is of great significance in the field of electric control of magnetism. Metal surface subsequent to semiconductor becomes another main stream with large Rashba SOC. In this paper, we review the recent progress in Rashba SOC in metal surfaces, including both the magnetic and nonmagnetic metal surfaces. We demonstrate the findings in Au(111), Bi(111), Gd(0001), etc., and discuss the possible factors that could influence Rashba SOC, including the surface potential gradient, atom number, the symmetry of the surface wavefunction, and the hybridization between the different orbitals in the surface states, etc. We also discuss the manipulation of Rashba SOC through electric field or surface decoration. In addition, on magnetic surface, there coexist Rashba SOC and magnetic exchange interaction, which provides the possibility of controlling magnetic properties by electric field through Rashba SOC. The angle-resolved photoemission spectroscopy and the first-principles calculations based on density functional theory are the two main methods to investigate the Rashba SOC. We review the results obtained by these two approaches and provide a thorough understanding of the Rashba SOC in metal surface.
Phase separation induced by density-spin interaction in one-dimensional extended t-J model
Authors: Mao Bin-Bin  , Cheng Chen  , Chen Fu-Zhou  , Luo Hong-Gang  ,   Center of Interdisciplinary Studies of Department of Physics, Lanzhou University, Lanzhou 730000, China;,   Beijing Computational Science Research Center, Beijing 100084, China
Published: December 2020

t-J model is one of important theoretical models in the study of high temperature superconductivity. Recent cold molecule experiments indicate that t-J model can be simulated by ultracold polar molecules. In the simulated t-J model, besides long-range dipolar interaction, density-spin interaction has also been introduced. In the present we study the effect of density-spin interaction in the one-dimensional extended t-J model by using the density matrix renormalization group method. We choose three sets of representative parameters, which correspond to three different phases in the ground state phase diagram of t-J model, to calculate the charge and spin density distribution in real space and the structure factor of density-density and spin-spin correlation functions. The results indicate that the nature of the system will not change if the intensity of the density-spin interaction is small, however if the intensity is large enough, the system enters the phase separation, in which the character is quiet different form that of the phase separation in the traditional t-J model.
The valley degree of freedom of an electron
Authors: Sun Jia-Tao  , Meng Sheng  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Collaborative Innovation Center for Quantum Matter, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Under the periodic potential of solid, the movement of an electron obeys the Bloch theorem. In addition to the charge and real spin degree of freedom, Bloch electrons in solids are endowed with valley degree of freedom representing the local energy extrema of the Bloch energy bands. Here we will review the intriguing electronic properties of valley degree of freedom of solid materials ranging from conventional bulk semiconductors to two-dimensional atomic crystals such as graphene, silicene, and transition metal dichalcogenides. The attention is paid to how to break the valley degeneracy via different ways including strain, electric field, optic field, etc. Conventional semiconductors usually have multiple valley degeneracy, which have to be lifted by quantum confinement or magnetic field. This can alleviate the valley degeneracy problem, but lead to simultaneously more complex many-body problems due to the remnant valley interaction in the bulk semiconductor. Two-dimensional materials provide a viable way to cope with the valley degeneracy problem. The inequivalent valley points in it are in analogy with real spin as long as the inversion symmetry is broken. In the presence of electric field, the nonvanishing Berry curvature drives the anomalous transverse velocity, leading to valley Hall effect. The valley degree of freedom can be coupled with other degree of freedom, such as real spin, layer, etc, resulting in rich physics uncovered to date. The effective utilization of valley degree of freedom as information carrier can make novel optoelectronic devices, and cultivate next generation electronics–valleytronics.
Changes of micro zone luminescent properties and stress of GaN-based light emitting diode film grown on patterned silicon substrate, induced by the removal of the substrate and AlN buffer layer
Authors: Zhang Chao-Yu  , Xiong Chuan-Bing  , Tang Ying-Wen  , Huang Bin-Bin  , Huang Ji-Feng  , Wang Guang-Xu  , Liu Jun-Lin  , Jiang Feng-Yi  ,   National Engineering Technology Research Center for LED on Si Substrate, Nanchang University, Nanchang 330047 China;,   LED Light Source and Lighting Research Center, Minnan Normal University, Zhangzhou 36300, China
Published: December 2020

At present, there are mainly two kinds of methods to prevent crack and reduce tensile stress of the silicon substrate GaN based light emitting diode (LED) epitaxial films: one is to use the patterned silicon substrate and the other is to grow a thick AlGaN buffer layer. The two kinds of methods have their own advantages and disadvantages. Although the patterned silicon substrate GaN based LED has industrialized and is gradually accepted by the market, there remain many scientific and technical problems, to be resolved, and a lot of research gaps worth studying deeply. Among these problems, to clearly investigate the different micro zone photoluminescence and the stress states in a single-patterned GaN based LED film grown on patterned silicon substrate. The studies of the stress interaction between the buffer layer and the quanturn well layer and the effect on the luminescent properties have important guiding significance for improving the quality and performance of the devices. Different micro zone photoluminescence (PL) properties in single-patterned GaN-based LED films grown on patterned silicon substrates, nondestructive free-standing LED thin film after removing away the silicon substrate, and the free-standing LED films after removing away the AlN buffer layer are studied. The variations of the bending degree of the free-standing LED thin films before and after removing away AlN buffer layer are inverstigated by using fluorescence microscopy and scanning electron microscopy. The results show as follows. 1) After removing away the silicon substrate, the free-standing LED film bends to the substrate direction in a cylindrical bending state. After removing away the AlN buffer layer, the LED film bends into flat. 2) For LED thin films on silicon substrates or off silicon substrates, their PL spectra have significant differences in different micro zones for the same pattern. When the AlN buffer layer is removed from the substrate its PL spectrum tends to be consistent in the different micro zones of the same pattern. When the patterned silicon substrate GaN-based LED thin film is removed from the silicon substrate, the PL spectrum is redshifted in each micro zone. After AlN buffer layer is removed from the substrate, the PL spectra present different degrees of blueshift in each micro zone. 3) The LED films before and after removing away the AlN buffer layer show some differences in droop effect.
Design and verification of microwave low frequency band-pass and high frequency band-stop composite structure
Authors: Huang Da-Qing  , Kang Fei-Yu  , Zhou Zhuo-Hui  , Liu Xiang  , Cheng Hong-Fei  ,   School of Material, Tsinghua University, Beijing 100084, China;,   Beijing Institute of Aeronautical Materials AVIC, Beijing 100095, China
Published: December 2020

It is important and urgent to develop microwave low frequency band-pass and high frequency band-stop composite structures according to the needs of marine environment stealth weapons and equipment constructions. In this paper, a hollow hexagonal periodic structure is originally designed and the microwave band-pass and band-stop characteristics are investigated through the CST software simulation. As an optimization result, the numerical periodic structure parameters of hexagon ring are as follows: hexagon ring side length is 2.7 mm, line width 0.5 mm and gap width 0.15 mm, which shows a transmission of 83% at 0-2 GHz, and meanwhile a shielding efficiency of more than 10 dB at 8-18 GHz, thereby basically justifying our design target. On this basis, a new type of double-layers' composite frequency selective surface (FSS) structure which is composed of facial layer, hollow hexagon ring array 1, middle spacer layer, hollow hexagon ring array 2 and another facial layer stacked layer by layer, is creatively designed, which displays excellent microwave low frequency band-pass and high frequency band-stop performances compared with a single layer hollow hexagonal periodic structure, and by simulation and optimization, structural parameters of the upper FSS structure are as follows: hexagon ring side length is 3.0 mm, line width 0.5 mm, gap width 0.4 mm, and the lower FSS structure parameters are as follows: hexagon ring side length is 3.2 mm, line width 0.5 mm, gap width 1.0 mm; simulation results show itself that dual different layers' FSS design presents itself excellent low frequency band-pass and high frequency band-stop transformation characteristics, and the fast switch capacity is the basic foundation for both excellent low frequency band-pass and outstanding high frequency band-stop characteristics. The effects of wave incidence angle (TE) on electrical performance of dual-layers FSS are investigated and the results indicate that the designed dual-layers' FSS possesses a wide angle insensitivity in a range of 0-45°, which is especially beneficial to engineering applications. Finally the composite structures with dual-layers' FSSs are manufactured and verified, and high transmission up to 95.6% at 0-2 GHz frequency band and more than 10 dB shielding efficiency at 7.05-18 GHz are obtained, which strongly testifies our design idea and has important significance for developing the high performance band-pass and band-stop composite structure and new electromagnetic functional composite materials.
Mechanism of neural information processing of sound localization by interaural level difference
Authors: Zhang Hong  , Ding Jiong  , Tong Qin-Ye  , Cheng Qian-Liu  ,   Department of Biomedical Engineering, Zhejiang University, Hangzhou 310027, China;,   Key Laboratory of Biomedical Engineering of Ministry of Education, Zhejiang University, Hangzhou 310027, China;,   Institute of Industry and Trade Measurement Technology, College of Metrology and Measurement Engineering, China Jiliang University, Hangzhou 310018, China;,   Key Laboratory of Sonar Technology, 715th Research Institute of China Shipbuilding Industry Corporation, Hangzhou 310023, China
Published: December 2020

More attention should be paid to the neural system, which is a quantitative system. There are few reports about the quantitative research on neural system. It will hinder the quantitative studies on animal binaural sound localization. The existing physiological experiments have found that there is a monotonic increase/decrease relationship between the input sound levels and the output spike frequencies of auditory neurons, so the variations of input sound level can be simplified into the change of output spike frequency of auditory neurons. In this paper, based on the theory of circle map and symbolic dynamics, a quantitative model of auditory neural circuitry is presented. In this neural circuit model, the neurons of ipsilateral input circuit propagate the action potentials as excitatory inputs, the neurons of heterolateral input one propagate the action potentials as inhibitory inputs. We also use a chemical neuronal model, which shows that the neurotransmitters released from pre-synapse vesicles have characteristics of quantitative release. The strength of the coupling between two neurons is represented by a coupling coefficient. The relationship between the input/output spike sequences of neural circuitry is simulated by using an Hodgkin-Huxley equation. In the range of simulating parameters, there is a monotonic increase/decrease phenomenon between input and output spike frequency. For the neuron with a single input and output structure, it is symbolized according to the method of symbolic dynamics; for the neurons with multi-input and single output structure, the output spike time will be used to detect the input spike frequency variations which are caused by the changes of interaural level difference (ILD), and the binaural level differences from those spike sequences are analyzed to locate the source of the sounds. With the increase of output spikes, the length of symbolic sequence increases, the symbolic sequence is sensitive to the variation of input signal. The simulation results show that the quantitative model proposed in this paper is able to detect the ILD signals by neural spike sequences.
Measurement of ion temperature by ion-acoustic waves Landau damping in oxide cathode plasma
Authors: Hu Guang-Hai  , Jin Xiao-Li  , Zhang Qiao-Feng  , Xie Jin-Lin  , Liu Wan-Dong  ,   CAS Key Laboratory of Plasma Physics, Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Ion temperature is one of the fundamental plasma parameters, which is important for studying the plasma behavior and instabilities. The measurement of ion temperature is very difficult especially in a low temperature plasma. The traditional passive and active (laser induced fluorescence) spectral diagnostics are complex and expensive because of the low value of the ion temperature, while the resolution of the retarding energy analyzer is not fine enough to measure the small T_i. Here we utilize the method of ion acoustic wave Landau damping to measure the ion temperature in the linear magnetized plasma device, where the 2 meter long plasma column with 12 cm in diameter is produced by an indirectly heated oxide cathode plasma source. The device provides a wide range of plasma parameters for many fundamental issues of plasma research. The typical plasma density is 2×1017 m-3 and neutral argon pressure is 0.02 Pa. Discharge pulse length is 5.8 ms with a plateau period of 4.8 ms. Ion acoustic waves (IAWs) are excited via biased plane stainless mesh grid with a high transparency of 80%. The grid with 10 cm in diameter is located in the center of the device (1.5 m away from the plasma source), while its normal axis is parallel to the magnetic field lines. Ion acoustic waves are excited during the discharge pulse via the sine signals applied to the grid. The biasing peak-peak voltage is 12 V with frequencies of 800 kHz and 1 MHz. IAW is also excited with biasing voltage 24 V and frequency 800 kHz, while the experimental results exclude the existence of the ion burst mode. A movable Langmuir probe controlled by a step motor is used to measure the spatial evolution of the IAW along the magnetic field. Thus the damping length and the phase velocity of the IAW propagating in the magnetic field are measured under different conditions. The measured phase velocity is around 3200 m/s in plasma coordinate. The electron temperature is measured to be 2.9 eV resulting from the V-I curve of single probe. Based on the measured damping length, the ion temperature is measured to be 0.3 eV, which is very consistent with the results measured by spectral diagnostics on other similar linear machines.
A new approach for influence maximization in complex networks
Authors: Hu Qing-Cheng  , Zhang Yong  , Xu Xin-Hui  , Xing Chun-Xiao  , Chen Chi  , Chen Xin-Hua  ,   Research Institute of Information Technology, Tsinghua National Laboratory for Information Science and TechnologyDepartment of Computer Science and Technology, Tsinghua University, Beijing 100084, China
Published: December 2020

Influence maximization modeling and analyzing is a critical issue in social network analysis in a complex network environment, and it can be significantly beneficial to both theory and real life. Given a fixed number k, how to find the set size k which has the greatest influencing scope is a combinatory optimization problem that has been proved to be NP-hard by Kempe et al. (2003). State-of-the-art random algorithm, although it is computation efficient, yields the worst performance; on the contrary, the well-studied greedy algorithms can achieve approximately optimal performance but its computing complexity is prohibitive for large social network; meanwhile, these algorithms should first acquire the global information (topology) of the network which is impractical for the colossal and forever changing network. We propose a new algorithm for influence maximization computing-RMDN and its improved version RMDN++. RMDN uses the information of a randomly chosen node and its nearest neighboring nodes which can avoid the procedure of knowing knowledge of the whole network. This can greatly accelerate the computing process, but its computing complexity is limited to the order of O(klog(n)). We use three different real-life datasets to test the effectiveness and efficiency of RMDN in IC model and LT model respectively. Result shows that RMDN has a comparable performance as the greedy algorithms, but obtains orders of magnitude faster according to different network; in the meantime, we have systematically and theoretically studied and proved the feasibility of our method. The wider applicability and stronger operability of RMDN may also shed light on the profound problem of influence maximization in social network.