bluuebunny/crossref_metadata_2025 huggingface dataset:
Angular distribution of characteristic X-ray emission from Fe and V following photoionization
Authors: Liu Yu , Xu Zhong-Feng , Wang Xing , Zeng Li-Xia , Liu Ting ,   School of Science, Xi’an Jiaotong University, Xi’an 710049, China,   Ion Beam and Optical Physical Laboratory, Xianyang Normal University, Xianyang 712000, China
Published: December 2020

 The de-excitation process of vacancy in the inner shell of the target atom caused by collision ionization produces the characteristic X-ray or Auger electrons. The precise measurement of ionization cross sections plays an important role in many basic research fields, as well as in practical fields, such as chemical analysis of Particle Induced X-ray Emission (PIXE), atomic and nuclear processes, and X-ray fluorescence (XRF) spectroscopy. As we know, when ionization cross sections are measured precisely, whether the emission of X-ray is isotropic in collision process must be considered. However, there have been few experimental results for angular dependence of Kβ/Kα intensity ratios in the literature until now. Therefore, this study aims to verify that the Kα and Kβ X-rays originated from filling of the K shell vacancies with total angular momentum quantum number 1/2 (J = 1/2) are isotropic.

 In this work, the typical K-shell X-ray spectra for Fe and V, which induced by bremsstrahlung with central energy of 13.1 keV, have been measured at emission angles varied from 120° to 170° at intervals of 10°. The characteristic X-ray spectra obtained by the detector are fitted by Gauss function, where the absorption of incident X-rays by the detector, the absorption of emitted X-rays by the atmosphere and the self-absorption correction factor of incident and emitted X-rays by the target are all taken into account.

 The experimental results of Kβ/Kα intensity ratio in this experiment coincide with those of theoretical calculation, as well as the Ertuğral’s experimental result. The experimental results show that the intensity ratio of Kβ/Kα is a constant at different detection angles. Therefore it can be concluded that the emission of Kα and Kβ is isotropic in the detection range. Since the K shell has no sub-shell, there is no Coster-Kronig transition in the collision ionization process. In the process of photoionization, the vacancies in the K shell are produced by direct ionization. As a result, the cross section ratio of K shell X-ray generation is independent of the K shell photoionization cross section. In addition, the experimental results show that the Kβ/Kα characteristic X-ray intensity ratio of target Fe is 8% higher than that of target V, which are consistent with the theoretical analysis results that the characteristic X-ray intensity ratio depends on the target atomic number Z.
Influence of incident illumination on optical scattering measurement of typical photoresist nanostructure
Authors: Dong Zheng-Qiong , Zhao Hang , Zhu Jin-Long , Shi Ya-Ting ,   Hubei Key Laboratory of Manufacture Quality Engineering, Hubei University of Technology, Wuhan 430068, China,   State Key Laboratory for Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Optical scatterometry, as a fast, low-cost, and non-contact measurement instrument, is widely used in the profile characterization of nanostructure in the semiconductor manufacturing industry. In general, it involves two procedures, i.e. the forward optical modeling of sub-wavelength nanostructures and the reconstruction of structural profiles from the measured signatures. Here, the general term signature means the scattered light information from the diffractive grating structure, which can be in the form of reflectance, ellipsometric angles, Stokes vector elements, or Mueller matrix elements. The profile reconstruction process is an inverse problem with the objective of optimizing a set of floating profile parameters (e.g., critical dimension, sidewall angle, and height) whose theoretical signatures can best match the measured ones through regression analysis or library search.

During solving the inverse problem, the refractive index and distinction coefficient of the material of nanostructure are assumed to be constants and they are generally fixed. This assumption is valid for most of the materials in semiconductor industry, but not for certain materials that are very photosensitive. That is, the optical constants of photosensitive materials may vary with the illumination time of the incident light beam in spectroscopic ellipsometer, and the error caused by the variation of optical constants propagates to the final extracted results of structural profiles, which should not be neglected, especially for high precision and accuracy metrology.

Experiments performed on SiO2 and polymethyl methacrylate (PMMA) thin films are conducted and demonstrate that the extracted geometric parameters and optical constants of SiO2 film do not change with illumination time increasing, while the twenty groups of values of extracted refractive index n and distinction coefficient k of PMMA resist film vary obviously, and the difference between the extracted maximum and minimum film thickness has reached 40.5 nm, which to some extent illustrates that the above assumption is not valid for PMMA resist, so that the incident light beam of spectroscopic ellipsometer has a great influence on the extracted film thickness. Further, simulations based on a three-dimensional PMMA grating also indicate that the error of optical constant has considerably transferred to the extracted profile parameters. This finding is of significance for improving the accuracy of nanostructure characterization in optical scatterometry.
Efficiency improvement in solution-processed multilayered phosphorescent white organic light emitting diodes by silica coated silver nanocubes
Authors: Zhang Ya-Nan , Zhan Nan , Deng Ling-Ling , Chen Shu-Fen ,   School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China,   College of Electronic and Optical Engineering & College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing 210023, China,   Key Laboratory of Organic Electronics and Information Displays, College of Materials Science and Engineers, Nanjing University of Posts & Telecommunications, Nanjing 210023, China
Published: December 2020

Localized surface plasmon resonance (LSPR) effect of metal nanoparticles (MNs) has been widely applied in organic light-emitting diodes (OLEDs) to improve the radiation of excitons. The LSPR wavelength and intensity of MNs and the coupling between MNs and excitons greatly affect the LSPR effect on exciton radiation. In this work, silica coated silver nanocubes (Ag@SiO2 NCs) were doped in the electron transport layer (ETL) of a solution-processed multilayered white OLED (WOLED). Due to the sharp edges and corners, Ag NCs have strong LSPR effect and can effectively enhance the radiation of nearby excitons. With an appropriate concentration of Ag@SiO2 NCs, the WOLED achieved two fold improvement in the current efficiency comparing with the control device without Ag@SiO2 NCs incorporated. The working mechanism of the Ag@SiO2 NCs based WOLED was investigated in detail. For the solution-processed OLED, excitons usually form and recombine near the interface of emission layer and electron transport layer (EML/ETL) because the commonly used host material (such as polyvinylcarbazole, PVK) has the unipolar hole transport property. So the Ag@SiO2 NCs in ETL greatly enhanced the radiation of the excitons located near the EML/ETL interface, which mostly contributed to the performance enhancement of the Ag@SiO2 NCs based WOLED. Study on a group of devices with Ag@SiO2 NCs doped in different locations indicated that Ag@SiO2 NCs in ETL showed more effective LSPR effect than those in hole injection layer. Electroluminescence and photoluminescence spectra of the WOLEDs declared that the Ag@SiO2 NCs simultaneously improved the radiation intensities of the blue and yellow excitons and helped the WOLED maintain the good chromaticity stability, which was mainly attributed to the wide LSPR wavelength range (450–650 nm) of the Ag@SiO2 NCs. The SiO2 coating layer of the Ag@SiO2 NCs played the important role in the LSPR enhanced emission. On the one hand, it formed an appropriated distance between the Ag NCs and the extions, helping to generate the strong coupling between them. On the other hand, it suppressed the effect of Ag NCs on charge trapping, keeping the stability of the carrier transport in the device. Our research demonstrate MNs can effectively improve the performance of OLEDs by carefully designing the device structure.
Tight focus and field enhancement of terahertz waves using a probe based on spoof surface plasmons
Authors: Wang Xiao-Lei , Zhao Jie-Hui , Li Miao , Jiang Guang-Ke , Hu Xiao-Xue , Zhang Nan , Zhai Hong-Chen , Liu Wei-Wei ,   Institute of Modern Optics, College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300350, China,   Key Laboratory of Optoelectronic Technology of Jiangsu Province, School of Physical Science and Technology, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

In order to improve the resolution of terahertz near-field microscopic imaging technology, an ultra-thin thickness-graded silver-plated strip probe with the same duty cycle is designed to realize the excitation of spoof surface plasmons. By comparing with two other probes with different structures, it can be found that the thickness-graded silver-plated strip probe can produce a strong electric field enhancement effect. Thereafter, the influence of the polarization direction of the incident electric field and the number of periodic metal stripes on the electric field which are generated at the tip of the probe is investigated. It is found that this case is highly consistent with the electric field distribution in Richards-Wolf vector diffraction theory when the incident light is linearly polarized. The electric field intensity generated at the tip of the thickness-graded silver-plated strip probe can be flexibly and effectively manipulated by changing the polarization direction of the incident electric field. When the number of thickness-graded silver-plated strips is 12, the minimum size of the focal spot is 20 μm, which is λ/150. When the number of thickness-graded silver-plated strips is 4, the electric field intensity enhancement factor at the focal spot is 849. The electric field intensity enhancement factor at the focal spot increases continuously as the number of periodic metal stripes increases, and the size of focal spot decreases continuously as the number of periodic metal stripes decreases. This result shows that the tight focusing and electric field enhancement of terahertz waves can be achieved by using an ultra-thin thickness-graded silver-plated strip probe. The research results in this paper have important guiding significance for manipulating the electric field in the terahertz band.
Spatial resolution of novel liquid scintillating capillary array
Authors: Zhang Mei , Li Kui-Nian , Li Yang , Sheng Liang , Zhang Yan-Hong ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi’an 710024, China
Published: December 2020

Scintillating array image plates are allowed high resolution through a thicker detector which increases quantum efficiency without degrading the imaging resolution substantially. Due to limitations imposed by process capability, scintillator fiber array with pixel diameter less than 0.2 mm is hardly manufactured to improve performance. Therefore, a liquid scintillator capillary array with 0.1 mm pixel is developed to improve the detection efficiency and spatial resolution of image plate for low intensity radiation imaging. Its performances are studied and tested by simulation and experiment, and are compared with those of scintillating fiber array. Especially in order to gain high fidelity representation of modulation transfer function of the array image plate, a method of simulating and measuring the slanted knife edge response and an iterative algorithm are introduced. For 14 MeV neutron and 1.25 MeV gamma, the slanted knife edge responses of these array image plates with pixel dimensions in a range from 0.1 mm to 0.5 mm are respectively simulated by MCNPx program and the modulation transfer function (MTF) are obtained. The simulation results show that compared with scintillating fiber array, the liquid scintillator capillaries array has an obvious merit in spatial resolution because of greater stopping power for secondary charged particle in the capillary quartz glass wall with 0.02 mm in thickness. Its ultimate resolution can reach to 1.8 lp/mm for 14 MeV neutron by simulation. At the 4000 Ci 60Co facility, a 5-cm-thick tungsten bar, one side of which has a curvature of 0.1 radian to minimize the misalignment effect, is made a knife edge. The MTF of the scintillating fiber array with 0.3 mm and 0.5 mm pixel and newly developed liquid scintillator capillary array is measured through this tungsten knife edge. Experimental measurement results have also verified that the liquid scintillator capillary array performs well in spatial resolution and luminescent uniformity for 1.25 MeV gamma. The ultimate spatial resolution, 0.9 lp/mm is gained, and those of other scintillating fiber arrays are all less than 0.5 lp/mm. Moreover, experimental test validates the simulating method and simulated results, although the measured value is slight less than the simulated value because of the effect of dimension of 60Co source.
Experimental research on influence of turbine guide vane on propagation characteristics of rotating detonation wave
Authors: Wei Wan-Li , Weng Chun-Sheng , Wu Yu-Wen , Zheng Quan ,   National Key Laboratory of Transient Physics, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

Detonation is a supersonic combustion in which a shock wave propagates driven by an energy release in a reaction zone. Compared with deflagration, detonation has high thermodynamic efficiency and fast heat release rate. The traditional propulsion system based on the isostatic combustion is relatively mature, and its performance is very difficult to further improve. Therefore, detonation is expected to improve the performance of the propulsion system. Replacing the isobaric combustion chamber of turbojet engine with rotating detonation combustor can not only improve the combustion chamber efficiency, but also reduce the number of compressor stages, reduce the weight of engine and simplify the structure of engine. In order to study the operation characteristics of rotating detonation combustor with a turbine guide vane, a series of experiments is conducted, with hydrogen used as fuel and air as oxidant at different equivalence ratios. Based on the signals of high frequency pressure sensor and static pressure sensor, the operation mode of rotating detonation combustor and the effect of a turbine guide vane on the inhomogeneous and unstable detonation products are analyzed in detail. The experimental results show that when the equivalent ratio is less than 0.5, the rotating detonation combustor operates in a rapid deflagration mode and the pressure of combustion wave is about 0.6 bar (1 bar = 105 Pa). The rotating detonation combustor begins to operate in an unstable rotating detonation mode when the equivalence ratio increases to 0.6, and the pressure of detonation wave is about 6 bar. The rotating detonation combustor operates in a stable rotating detonation mode when the equivalence ratio reaches 0.82, and the pressure of detonation wave is about 16.3 bar. In addition, the propagation velocity gradually increases and the stability improves with the increase of the equivalence ratio. The oblique shock wave interacts with the turbine guide vane, and part of the oblique shock wave is reflected back to combustor, which causes some small pressure fluctuations in combustor. The turbine guide vane can obviously suppress the amplitude of pressure oscillation, but has little effect on the frequency of pressure oscillation. The upstream and downstream static pressure of the turbine guide vane increase simultaneously with equivalence ratio increasing. Furthermore, the static pressure of detonation products decreases obviously after passing through the turbine guide vane.
Microstructure and thermoelectric property of (Bi1–xTbx)2(Te0.9Se0.1)3 fabricated by high pressure sintering technique
Authors: Zou Ping , Lü Dan , Xu Gui-Ying ,   School of Materials Science and Engineering, Guizhou Minzu University, Guiyang 550025, China,   School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

Nanocrystalline bulk materials n-type (Bi1–xTbx)2(Te0.9Se0.1)3 (x = 0, 0.002, 0.004, 0.008) are fabricated by high pressure sintering (HPS) technique. The HPS samples are then annealed for 36 h in a vacuum at 633 K. The phase compositions and crystal structure of HPS sample are analyzed by X-ray diffraction. The microscopic morphology of HPS sample is observed by field-emission scanning electron microscopy. The electric conductivity, Seebeck coefficient, and thermal conductivity of the HPS sample and annealed sample are measured in a temperature range from room temperature to 473 K. The effects of Tb content on crystal structure and thermoelectric properties of the sample are systematically studied. The results show that HPS sample consists of nanoparticles. With the increase of content of Tb, the cell volume increases. Besides, the power factor increases but thermal conductivity decreases through doping Tb, thus the optimal figure of merit (ZT) value increases. The Tb doping amount of x = 0.004 is an optimal doping amount. At this doping amount, the maximum ZT of 0.29 is achieved, which is enhanced by 32% compared with the ZT value of undoped sample. The thermoelectric performance can be improved significantly by annealing. The thermal conductivity of the annealed sample with x = 0.004 is 0.9 W·m–1·K–1 at 373 K, decreased by 23% compared with the thermal conductivity of HPS sample. Consequently, the ZT value of annealed sample is significantly higher than that of HPS sample. The maximum thermoelectric ZT of 0.99 is achieved for annealed sample with x =0.004 at 373 K. Furthermore, it is worthwhile to note that this annealed sample possesses a ZT value larger than 0.8 when the temperature is higher than 323 K.
Monitoring of ambient methane and carbon dioxide concentrations based on wavelength modulation-direct absorption spectroscopy
Authors: Wang Zhen , Du Yan-Jun , Ding Yan-Jun , Peng Zhi-Min ,   State Key Laboratory of Power Systems, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

Wavelength modulation-direct absorption spectroscopy (WM-DAS) integrates the advantages of measuring absolute absorbance profile from calibration-free direct absorption spectrum (DAS) with the enhanced noise rejection and high sensitivity of wavelength modulation spectrum (WMS). This method can be used to precisely recover the crucial absorbance profile via the extraction of the characteristic frequency of the modulated transmitted light. In this paper, the WM-DAS method with non-calibration and high signal-to-noise ratio is integrated with a Herriott cell (about 128 m). Under the condition of atmospheric pressure and room temperature, the absorptance functions of two spectral lines of CO2 (6330.821 cm–1) and CH4 (6046.964 cm–1) in air are measured, and their standard deviations of spectral fitting residual are 5.6 × 10–5 and 7 × 10–5, respectively. Subsequently, the concentration of CO2 and CH4 in air are monitored on-line by the WM-DAS method integrated with the Herriott cell, and compared with those by the highly sensitive continuous wave cavity ring down spectroscopy (CW-CRDS). The experimental results show that the measured results of the long optical path WM-DAS method are consistent with those by the CW-CRDS method, and the linear correlation between the two methods is above 0.99. The detection limit of CO2 and CH4 by the WM-DAS method are 170 ppb and 1.5 ppb respectively, which are slightly higher than those by the CW-CRDS. However, the measurement speed by WM-DAS is much higher than that by CW-CRDS, and possesses the advantages of simpler operation, lower environmental requirements, long-term stability, etc.
Pulsar candidate selection based on self-normalizing neural networks
Authors: Kang Zhi-Wei , Liu Tuo , Liu Jin , Ma Xin , Chen Xiao ,   College of Computer Science and Electronic Engineering, Hunan University, Changsha 410082, China,   College of Information Science and Engineering, Wuhan University of Science and Technology, Wuhan 430081, China,   College of Instrument Science and Opto Electronic Engineering, Beihang University, Beijing 100191, China,   Shanghai Institution of Satellite Engineering, Shanghai 200240, China
Published: December 2020

Pulsar candidate selection is an important step in the search task of pulsars. The traditional candidate selection is heavily dependent on human inspection. However, the human inspection is a subjective, time consuming, and error-prone process. A modern radio telescopes pulsar survey project can produce totally millions of candidates, so the manual selection becomes extremely difficult and inefficient due to a large number of candidates. Therefore, this study focuses on machine learning developed in recent years. In order to improve the efficiency of pulsar candidate selection, we propose a candidate selection method based on self-normalizing neural networks. This method uses three techniques: self-normalizing neural networks, genetic algorithm and synthetic minority over-sampling technique. The self-normalizing neural networks can improve the identification accuracy by applying deep neural networks to pulsar candidate selection. At the same time, it solves the problem of gradient disappearance and explosion in the training process of deep neural networks by using its self-normalizing property, which greatly accelerates the training process. In addition, in order to eliminate the redundancy of the sample data, we use genetic algorithm to choose sample features of pulsar candidates. The genetic algorithm for feature selection can be summarized into three steps: initializing population, assessing population fitness, and generating new populations. Decoding the individual with the largest fitness value in the last generation population, we can obtain the best subset of features. Due to radio frequency interference or noise, there are a large number of non-pulsar signals in candidates, and only a few real pulsar signals exist there. Aiming at solving the severe class imbalance problem, we use the synthetic minority over-sampling technique to increase the pulsar candidates (minority class) and reduce the imbalance degree of data. By using k-nearest neighbor and linear interpolation to insert a new sample between two minority classes of samples that are close to each other according to certain rules, we can prevent the classifier from becoming biased towards the abundant non-pulsar class (majority class). Experimental results on three pulsar candidate datasets show that the self-normalizing neural network has higher accuracy and faster convergence speed than the traditional artificial neural network in the deep structure, By using the genetic algorithm and synthetic minority over-sampling technique, the selection performance of pulsar candidates can be effectively improved.
Dual mirror evolutions of Airy beams propagating through uniaxial crystals induced by added spherical phase
Authors: Zhu Kai-Cheng , Liang Rui-Sheng , Yi Ya-Jun , Liu Wei-Ci , Zhu Jie ,   Department of Electronics and Information Engineering, Guangzhou College of Technology and Business, Guangzhou 510850, China,   School of Physics and Electronics, Central South University, Changsha 410083, China,   College of Science, Guizhou Institute of Technology, Guiyang 550003, China
Published: December 2020

Airy beams have received considerable attention due to their unique features on propagation, including non-spreading, self-healing, self-accelerating, and parabolic trajectories. Here in this work we study the propagation of linearly polarized Airy beams with an added spherical phase in uniaxial crystal orthogonal to the optical axis. Based on the beam transmission theory in uniaxial crystals, the analytical expressions for the intensity distribution of the beams in different view planes are derived. Numerical calculations are performed and some novel propagation features are presented graphically. It is shown that the Airy beam with an added spherical phase remains linearly polarized but cannot keep other properties unchanged during propagation in uniaxial crystal. Such a beam maintains its intensity profile in the near-field, then with the propagation distance increasing, converts into the Gaussian-Airy beams with different orientations at two specified distances which are codetermined by the extraordinary and ordinary refractive index of the crystal (namely ne and no) and the radius of the spherical phase, and most impressively, forms a mirror-like reflection profile in the far field, i.e., the intensity pattern in the far field returns to the initial Airy beam profile while its orientation on the transversal plane is reversed along the bisector line of the second and fourth quadrant. Note that the intensity pattern successively experiences two mirror transformations along the x and y coordinate axis when passing through these two critical positions, which can give rise to the mirror reflection effect for the whole Airy beam. Moreover, we further demonstrate that the sequences of these two mirror transformations are in close relation with the relative size between ne and no. Therefore, the results obtained in this paper reveal new propagation features in anisotropic medium of Airy beams with added spherical phase and provide a novel route to controlling propagation properties like the pattern profile and orientation of the Airy beams through choosing appropriate anisotropic materials and the radius of the spherical phase factor. Considering that it is easy to obtain an Airy beam with an added spherical phase which can be realized with an Airy beam through an ideal lens, our investigation may lead to potential applications in many fields where the ability to change profile and orientation of the intensity pattern and the ability to determine the refractive index of anisotropic medium are both required.
Near-field infrared microscopy of graphene on metal substrate
Authors: Cen Gui , Zhang Zhi-Bin , Lü Xin-Yu , Liu Kai-Hui , Li Zhi-Qiang ,   College of Physics, Sichuan University, Chengdu 610065, China,   School of Physics, Peking University, Beijing 100871, China
Published: December 2020

Graphene plasmons, collective oscillation modes of electrons in graphene, have recently attracted intense attention in both the fundamental researches and the applications because of their strong field confinement, low loss and excellent tunability. The dispersion of graphene plasmons can be significantly modified in the system of graphene on metal substrate, in which the screening of the long-range part of the electron-electron interactions by nearby metal can lead to many novel quantum effects, such as acoustic plasmons, quantum nonlocal effects and renormalization of band structure. Scattering-type scanning near-field optical microscopy (s-SNOM) which consists of a laser coupled to the tip of an atomic force microscopy (AFM), is an effective technique to directly probe plasmons in two-dimensional materials including graphene, and the graphene plasmons can be observed visually by real-space imaging. But so far the detailed s-SNOM studies of graphene/metal system have not been reported. One potential challenge is that the near-field response of highly conductive metal substrate may partially or entirely obscure that of graphene, making it difficult to further explore graphene by using s-SNOM. Here in this paper, we report the direct observation of near-field optical response of graphene in a graphene/metal system excited by a mid-infrared quantum cascade laser. From a close examination of the data of graphene/Cu compared with that of h-BN/Cu, we are able to identify experimental features due to the near-field response of graphene. Surprisingly, two completely different behaviors are observed in the s-SNOM data for different graphene samples on Cu substrates with similar surface step geometries. These results suggest that the near-field response of graphene/metal system is not completely dominated by the metal substrate, and that two completely different near-field response behaviors of graphene may be attributed to their intrinsic properties affected by metal substrates themselves rather than surface step geometries of metal substrate. In addition, following this approach it is possible to distinguish the near-field optical responses of graphene from that of graphene/metal system. Our work reveals the clear signatures of the near-field optical response of graphene on metal substrate, which provides the foundation for probing plasmons in these systems by using the s-SNOM and understanding many novel quantum phenomena therein.
Ferromagnetic resonance frequency and spin wave mode of asymmetric strip nanomagnet
Authors: Chen Ya-Bo , Yang Xiao-Kuo , Wei Bo , Wu Tong , Liu Jia-Hao , Zhang Ming-Liang , Cui Huan-Qing , Dong Dan-Na , Cai Li ,   Department of Foundation, Air Force Engineering University, Xi’an 710051, China,   Department of Wired Communications, Air Force Communications NCO Academy, Dalian 116100, China
Published: December 2020

Recently, the operating frequency of nanomagnetic logic device has reached the spin wave frequency of nanomagnets. Therefore, the dynamic magnetic properties of nanomagnets, which are excited by microwave magnetic field, have been explored by many researchers. In this paper, the micro-magnetic model of asymmetric strip nanomagnets under microwave excitation is established. By using the anisotropic stress field (along the x-axis direction) that is generated by a constant voltage and the SINC function microwave magnetic field (along the y-axis direction) to excite the nanomagnets at the same time, the effects of tilt angle and defect angle on the ferromagnetic resonance (FMR) spectrum and spin wave mode of the asymmetric strip nanomagnets are studied. Spectral analysis is performed on the micromagnetic simulation data. Simulation results show that as the tilt angle of the asymmetric strip nanomagnet increases, the ferromagnetic resonance frequency increases. What is more, this phenomenon is independent of the defect angle of the nanomagnet. When the tilt angle is constant, there exists a monotonically increasing relation between the ferromagnetic resonance frequency of the asymmetric strip nanomagnet and the defect angle. The spin wave modes of the nanomagnets differ a lot as defect angle changes. The asymmetric strip nanomagnet is compared with the rectangle nanomagnet, and the spin wave mode of the asymmetric strip nanomagnet is localized. Specifically, the spin wave mode of the asymmetric strip nanomagnets is asymmetric and the high precession region exists at the edge, which is termed asymmetric edge mode. The changes of the tilt angle lead to the changes in the demagnetizing field inside the nanomagnet, which gives rise to the movement of the edge mode. However, the center mode is not sensitive to the change of tilt angle. Finally, the magnetic loss of the model under the excitation of high frequency microwave magnetic field is analyzed and the reliability of the model is verified. These findings indicate that the defect angle and tilt angle can be used to tune the spin wave mode and the ferromagnetic resonance frequency of nanomagnets, and thus providing an important theoretical basis for designing the tunable microwave nanomagnetic devices.
Superconductivity in topological materials
Authors: Gu Kai-Yuan , Luo Tian-Chuang , Ge Jun , Wang Jian ,   International Center for Quantum Material, School of Physics, Peking University, Beijing 100871, China,   Collaborative Innovation Center of Quantum Matter, Beijing 100871, China,   CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China,   Beijing Academy of Quantum Information Sciences, Beijing 100193, China
Published: December 2020

In recent years, by introducing topological invariants into condensed matter systems, new phases of mater are revealed. Of these new phases, the topological insulator, topological semimetal and topological superconductor are the most important. They are called topological materials due to nontrivial topological parameters. Topological superconductors hold Majorana zero modes at the edges, satisfying non-abelian statistics, which makes them major candidate for realizing topological quantum computation. Besides exploring intrinsic topological superconductor, a promising way to realize topological superconductor is to induce superconductivity into other kinds of topological materials. Up to now, experimentalists have developed some techniques, such as gating, doping, high pressure, interface effect and hard point contact to introduce superconductivity into various topological materials, and also they have studied the topological properties of the induced superconductivity. In this review, we summarize the representative researches on intrinsic topological superconductor candidates and induced superconductivities in topological insulators and semimetals. The advantages and disadvantages of different techniques are discussed. Besides, the potential evidences of topological superconductors are analyzed. In the end, the outlook of this actively pursued research field is given.
Observation of the anisotropic exceptional point in cavity magnonics system
Authors: Zhang Gao-Jian , Wang Yi-Pu ,   Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou 310027, China
Published: December 2020

 We theoretically and experimentally demonstrate the anisotropic exceptional points (EPs) in the cavity magnonics system where magnons in a one millimeter-diameter yttrium iron garnet (YIG) sphere are coherently coupled with the microwave photons in a three-dimensional microwave cavity. The damping nature makes the cavity magnonics system inherently non-Hermitian. By solving the eigenvalues and eigenvectors of non-Hermitian Hamiltonian, a series of interesting and essential characteristics of the system can be obtained. Therefore, non-Hermitian physics has received more and more attention in both theory and experiment communities. Among them, exceptional points correspond to the non-Hermitian system’s degenerate states where the eigenvalues of the non-Hermitian system are identical, and the eigenvectors are parallel. The coupled cavity photon-magnon system has high tunability of coupling strength and cavity external damping rate, which is very suitable for studying EPs -related physics.

 Exceptional points (EPs) are crucial in all kinds of non-Hermitian physical systems, which have both fundamental and applicational importance. For instance, it can be used for sensitive detection by monitoring spectrum splitting of degenerate modes when a perturbation to be sensed occurs. The EPs can be anisotropic, which means that it has a different function relation when the system approaches the EPs along different parameter paths of the system. In this paper, by carefully designing the parameter space, we observe the anisotropic exceptional point in the coupled cavity photon-magnon system. It shows the linear and square-root behavior when the EPs are approached from different directions in the parameter space. One of the parameters is the position of the YIG sphere in the cavity, which determines the coherent coupling strength between the cavity mode and the magnon mode. Another parameter is the number of the gasket between the cavity signal loading port and the cavity external surface, which determines the external damping rate of the cavity mode. Both of these parameters can be easily and accurately adjusted experimentally.

 Our study paves the way for exploring anisotropic EPs based sensing technologies and more non-Hermitian related physics in the cavity magnonics system.
Numerical simulation of beam deflection for smoothed laser beams
Authors: Li Bin , Liu Zhan-Jun , Hao Liang , Zheng Chun-Yang , Cai Hong-Bo , He Min-Qing ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

When it reaches high energy density state, new features of laser propagation in plasma arises in the contrast to that of research field in classical optics. Such as beam deflection, a laser beam can change its propagation direction while it comes across a transverse plasma flow. On the other hand, employment of all sorts of smoothed laser beams becomes very common in high power laser facilities for high energy density physics experiments. Therefore, on what condition beam deflection comes into play for smoothed beams are necessary to be investigated. This paper presents numerical simulation results for that, which is performed by laser plasma interaction code LAP3D. It is a three dimensional massively parallel code, including a laser paraxial envelope solver and a nonlinear Eulerian hydrodynamics package, and models for filamentation, stimulated Raman scattering and stimulated Brillouin scattering, with beam smoothed by continuous phase plate (CPP), spectral dispersion (SSD), separately. For simplicity in this study, numerical simulations perform in a about 700 μm × 700 μm × 700 μm plasma using isotropic conditions (Te = 3 keV, Ti = 1 keV, n = 0.1 nc) and only include refraction and diffraction effects, namely, with filamentation model excluding scattering models. Simulation employs the CPP and the SSD beam as representatives of spatial and temporal smoothed beams, respectively, and uses an oval like focused spot with extension in the long axis direction about 200 μm in the focus plane propagating through the left boundary into the simulation domain. Based on our previous investigations, we assume that beam deflection of a smoothed beam becomes effective when it satisfies two following conditions as that for a Gaussian beam, namely, suffering filamentation and facing a transverse plasma flow at ion sound speed. Simulation results of LAP3D confirm that both spatial and temporal smoothed beams suffer beam deflection when two above conditions are both satisfied. For the case of CPP smoothed beam, simulation results show that it suffers evident beam deflection under the conditions that it suffers filamentation when its average intensity is larger than that of filamentation threshold, and faces a transverse plasma flow at ion sound speed. For the case of SSD smoothed beam, simulation results show that the beam can avoid beam deflection even if it faces a transverse plasma flow at ion sound speed when filamentation is suppressed as beam bandwidth is much larger than the growth rate of filamentation, otherwise it suffers beam deflection.
Macroscopic basic characteristics of a road network under the influence of traffic generation and attraction source agglomeration
Authors: Ding Heng , Zhou Jing-Wen , Zheng Xiao-Yan , Bai Hai-Jian , Zhang Wei-Hua ,   School of Automobile and Traffic Engineering, Hefei University of Technology, Hefei 230009, China
Published: December 2020

The macroscopic fundamental diagram (MFD), which can describe the macroscopic state of a regional network intuitively, describes a unimodal, statistical and reproducible relationship between accumulation and the trip completion flow of a region. Existing researches have proved that using MFD characteristics can ‘metering’ the boundary flow and relieve the traffic congestion problem effectively. As the foundation of traffic control, existing studies on the characteristic of MFD have proved that external origin to destination demand does not influence the MFD distribution. However, the traffic generation and attraction sources in the regional road networkwill changes the distribution of traffic density of the road network, thus affecting the characteristic of MFD. However, to date, no related analysis explored the influence of the traffic generation and attraction sourcesin the regional road network. To solve this problem, according to the spatial and temporal distribution of traffic generation and attraction sources in the regional road network, this paper puts forward an aggregation degree index analysis model of traffic generation and attraction sources, based on the dynamic parameters of traffic generation and attraction sources, and section traffic impedance. Taking a square-format road network as the target, nine groups of schemes for different traffic generation and attraction sources are designed. Two conclusions can be drawn after comparing the MFD curve of the road network under different aggregation degree index of traffic generation and attraction sources: (1) when the traffic flow of the road network is in the state of free flow or critical flow, the aggregation effect of traffic generation and attraction sources has no effect on MFD distribution; (2) when the traffic flow of the road network is in the congestion flow state, the aggregation effect of traffic generation and attraction sources influences MFD distribution. Moreover, under the same road network flow conditions, the aggregation degree of traffic generation and attraction sources is lower in the road network (the distribution of traffic generation and attraction volume is more balanced), the trip completion flow of road network will be higher. Otherwise, the aggregation degree of traffic generation and attraction sources is higher in the road network (the distribution of traffic generation and attraction volume is more unbalanced), the trip completion flow of road network will be lower.
Enhanced optical absorption of graphene by plasmon
Authors: Zhao Cheng-Xiang , Qie Yuan , Yu Yao , Ma Rong-Rong , Qin Jun-Fei , Liu Yan ,   Modern College of Humanities and Sciences of Shanxi Normal University, Linfen 041000, China,   College of Physics and Information Engineering, Shanxi Normal University, Linfen 041004, China,   Binjiang College, Nanjing University of Information Science & Technology, Wuxi 214105, China
Published: December 2020

The plasmons in graphene have the superior properties to metal surface plasmons, such as high field confinement, low Ohmic loss and long wave propagation, highly tunable via electrostatic. More importantly, the frequency of plasmons ranges from terahertz to infrared which indicates that graphene is an ideal candidate for terahertz plamsonics. On the other hand, the strong coupling between incident photons and plasmons in graphene can lead the optical absorption to be enhanced. However, it is difficult for light to couple directly with plasmons in graphene, for the momentum of incident photons cannot match the plasmons in graphene. A metal grating can be used to compensate for the momentum of photons so that it can match that of plasmons in graphene. In this work, we theoretically investigate the effect of plasmons on the terahertz optical absorption of graphene with grating based on finite difference time domain. A great enhancement of electric field component of light field can be obtained near the gold grating strip in the sheet of graphene. Thus, the photons, of which the momentum is compensated for by the grating, can strongly couple with plasmons in graphene. An obviously decrease of the transmission of the graphene structure can be seen at the resonant frequency. The transmission peak corresponds to the resonant frequency spliting into two peaks due to the fact that two plasmon polariton modes are formed by the coupling of photons and palsmons. So we also study the plasmon polariton modes made by coupling photon with palsmon based on the many-body self-consistent method. Two plasmon polariton modes are obtained and an obviously splitting at the resonant frequency can be seen due to the coupling between photons and plasmons. The work conduces to deepening the understanding of the photoelectric properties of graphene and the terahertz plasmonics based on graphene.
Discrete integrable systems: Multidimensional consistency
Authors: Zhang Da-Jun ,   Department of Mathematics, Shanghai University, Shanghai 200444, China
Published: December 2020

In contrast to the well-established theory of differential equations, the theory of difference equations has not quite developed so far. The most recent advances in the theory of discrete integrable systems have brought a true revolution to the study of difference equations. Multidimensional consistency is a new concept appearing in the research of discrete integrable systems. This property, as an explanation to a type of discrete integrability, plays an important role in constructing the Bäcklund transformations, Lax pairs and exact solutions for discrete integrable system. In the present paper, the multidimensional consistency and its applications in the research of discrete integrable systems are reviewed.
The research progress of topological properties in spinor Bose-Einstein condensates
Authors: Wang Li , Liu Jing-Si , Li Ji , Zhou Xiao-Lin , Chen Xiang-Rong , Liu Chao-Fei , Liu Wu-Ming ,   College of Physics, Sichuan University, Chengdu 610065, China,   Beijing Jingshan School Chaoyang Branch School, Beijing 100012, China,   College of Physics, Taiyuan Normal University, Jinzhong, 030619, China,   School of Physics and Electronic engineering, Sichuan Normal University, Chengdu 610101, China,   School of Science, Jiangxi University of Science and Technology, Ganzhou 341000, China,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Most of the atoms that realize Bose-Einstein condensation have internal spin degree of freedom. In the optical potential trap, the internal spin of the atom is thawed, and the atom can be condensed into each hyperfine quantum state to form the spinor Bose-Einstein condensate. Flexible spin degrees of freedom become dynamic variables related to the system, which can make the system appear novel topological quantum states, such as spin domain wall, vortex, magnetic monopole, skymion, and so on. In this paper, the experimental and theoretical study of spinor Bose-Einstein condensation, the types of topological defects in spinor Bose-Einstein condensate, and the research progress of topological defects in spinor two-component and three-component Bose-Einstein condensate are reviewed.