bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite difference time domain simulation of optical properties of annular cavity arrays
Authors: Zhou Jing  , Wang Ming  , Ni Hai-Bin  , Ma Xin  ,   Key Laboratory on Opto-Electronic Technology of Jiangsu Province, School of Physics Science and Technology, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

Optical properties of two-dimensional periodic annular cavity arrays in hexagonal packing are investigated by finite difference time domain simulation method in this paper. According to simulated reflectance/transmission spectra, electric field distribution and charge distribution, we confirm that multiple cylindrical surface plasmon resonances, which result in reflectance dips, can be excited in annular cavities by linearly polarized light. Mechanism of the cylindrical surface plasmons is investigated. A coaxial waveguide mode TE11 is excited in the annular cavities and a Fabry-Perot resonance is fulfilled along the depth direction of the annular cavities at the resonance wavelengths. While the number of reflectance dips and wavelengths of these dips in reflectance spectra are dependent on the geometric sizes of the annular cavities, the periodicity and polarization of incident light do not affect their reflectance spectra dramatically. Incident light beams with resonant wavelengths are localized in annular cavities with large electric field increasing and dissipate gradually due to metal loss. Reflectance dips can be tuned from 350 to 2000 nm by adjusting geometric size parameters of the annular cavities, such as outer and inner radii of the annular gaps, gap sizes and metal film thickness values. Reflectance dips shift toward longer wavelength with increasing inner and outer radii of the annular gaps, metal film thickness and with reducing the gap distance. In addition, infiltrate liquids in the annular gaps will result in a shift of the resonance wavelengths, which makes the annular cavities good refractive index sensors. A refractive index sensitivity up to 1850 nm/RIU is demonstrated. The refractive index sensitivities of annular cavities can also be tuned by their geometric sizes. Annular cavities with large electric field enhancement and tunable cylindrical surface plasmons can be used as surface enhanced Raman spectra substrates, refractive index sensors, nano-lasers and optical trappers.
Fractal dimensions and escape rates in the two-dimensional Hénon-Heiles potential and its deformation form
Authors: Zhang Yan-Hui  , Shen Zhi-Peng  , Cai Xiang-Ji  , Xu Xiu-Lan  , Gao Song  ,   College of Physics and Electronics, Shandong Normal University, Jinan 250014, China;,   College of Physics, Shandong University, Jinan 250100, China
Published: December 2020

From the beginning of the twentieth century the development of nonlinear theory has guided us into a new field of exploration; chaos and fractals are important tools widely used in studying the nonlinear system. Fractal focuses on the description of the physical geometry while Chaos emphasizes the research on the developing process of dynamics coupled with geometry. We have studied the nonlinear behavior of the particles in non-integrable system by means of chaos and fractals.#br#There are fractal structures in a Hénon-Heiles system, by which we can investigate the general escape law of particles in chaotic systems. The motion of particles is traced by dynamical algorithm within the framework of Chin and Chen (2005 Celestial Mechanics and Dynamics Astronomy 91 301). For the first time, we study the escape property of particles in Hénon-Heiles system and make a comparison with it in its hexagon-shaped form. Particles with energy higher than the threshold (1/6) can escape from the Hénon-Heiles system. The self-similar structures are found by calculating the escape time of particles with an energy higher than the threshold for different exit angles. We calculate the escape rate of particles with different energies and make a statistical analysis on the fractal dimensions by ‘box-counting' method. It is that the escape rate and fractal dimensions change with the energy of particles in the Hénon-Heiles system. Moreover, we find that the fractal dimensions are strongly linear with the escape rate.#br#To testify the universality of the conclusion, we calculate the escape rate and fractal dimensions of particles in the hexagon-shaped Hénon-Heiles system. Unlike the motion of particles in the Hénon-Heiles system, the escape of particles is divided into two ranges of energy. In low energy range, the escape rate and fractal dimensions of particles change with energy, which is similar to that in the Hénon-Heiles system. However, the escape rate and fractal dimensions tend to become stable in high energy range. But the general law is still valid–the fractal dimensions are strongly linear with the escape rate.#br#Therefore, the fractal dimensions can be served as a tool to study the escape features of particles in a chaotic system. We can characterize the transport behaviors in a chaotic electronic equipment by investigating the fractal dimensions in the design of mesoscopic devices.
Generation of a family of Pearcey beams and their optical structure
Authors: Ren Zhi-Jun  , Li Xiao-Dong  , Jin Hong-Zhen  ,   Key Laboratory of Optical Information Detecting and Display Technology, Zhejiang Normal University, Jinhua 321004, China;,   Institute of Information Optics, Zhejiang Normal University, Jinhua 321004, China
Published: December 2020

Based on differential geometry and optical diffraction theory, the determinants of optical structure of Pearcey beams are examined. We theoretically propose and experimentally observe a bundle of Pearcey beams with different optical topology structures. Besides, we have studied their properties and the results show that the structure of Pearcey beams can be flexibly controlled, hence they will be expected to play a new role in some research fields.
Simulation study of the colliding bulge and surface micro-jet of metal flyers driven by detonation
Authors: Liu Jun  , Fu Zheng  , Feng Qi-Jing  , Wang Pei  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

In the cylindrical implosion problem, the phenomenon of colliding bulge and surface micro-jet formation of two-layer metal flyers, which are driven by two slip detonations in opposite direction of the pole, is studied by simulation using Euler's program. Simulation results of the inner surface travel times of the lead flyer coincide well with the experimental results. In the polar position, there is a fracture cavity in the lead flyer, and a blunt bulge is formed on the inner surface. At the equator, large-scale fracture particles are generated as the inner surface of the lead flyer is growing. It is considered that the colliding bulge at the equator which seem to be continuous in the X-ray images is actually discontinuous, and it is composed of large-scale fracture particles and small-scale micro-jet particles. By analysis of the inner surface position on the optical images at different times, the maximum velocity of the lead micro-jet particles is obtained. It is found that the maximum velocity of the micro-jet particles is declined in the pole region, but at the equator its maximum velocity is increased with time. It is considered that the subsequent loading waves on the colliding bulge area may cause higher speed of micro-jet particles than the first loading wave. And then, the groove micro-jet model of the lead, which is loaded by impact, is used to be equivalent to the uniform disfigurement surface micro-jet. It is proved that both the micro-jet maximum velocity in the pole region and the velocity at the equator can be formed by the same uniform disfigurement surface, and the correctness of the experimental optical image is also verified. Finally, the restrained method of the colliding bulge and surface micro-jet in this problem is studied by simulation. The micro-jet maximum velocity of the lead flyer can be declined by changing the two opposite initiation points to the points close to the metal flyers in the pole region, and the main cause of collision bulge at the equator is that the Mach reflection is formed in the collision area because of the low sound velocity of lead.
Preparation and charge storage property of FEP thin film electret with grid electric field distribution in millimeter scale
Authors: Zhang Lin-Cheng  , Chen Gang-Jin  , Xiao Hui-Ming  , Cai Ben-Xiao  , Huang Hua  , Wu Ling  ,   Hangzhou Dianzi University, Lab of Electret and Its Application, Hangzhou 310018, China
Published: December 2020

Electret has caught wide attention because it can produce a lasting and stable electrostatic field in the application of MEMS devices such as miniwatt electret generator, electret motor, electret sensor, electret transducer, and so on. Of all the above applications, a remarkable feature is that the electrostatic field distribution on electret surface is patterned in millimeter size or even smaller. However, the charge storage performance of electret in miniature size will dramatically get worse in contrast with the macro-electret. Therefore, it is very important to develop an applicable preparing method to maintain the stability of electrostatic field distribution in micro-patterned electret. In this paper, it is reported that a fluorinated ethylene propylene copolymer (FEP) with evaporated aluminum grid electrode a 25 m thickness topped with at a step of 2 or 3 millimeter are successfully prepared to form the electret with well grid distribution of electric field(abbreviated as grid electret) by means of corona charging and thermal charging technology. Effect of grid width and charging temperature on the charge storage performance is studied. After stored for 150 days, the grid distribution of electric field on the FEP surface becomes clear and organized. The potentials of the area covered by aluminum electrode are close to zero, while that of uncovered area still remain high. The potential differences between the covered and uncovered by aluminum electrode area are identical in different charging methods, it is 110 V (electric field 44 kV/cm) for the sample with an electrode width of 2 mm, and 130 V (electric field 52 kV/cm) for the sample with an electrode width of 3 mm. Results also show that the initial surface potentials of the grid electrets prepared by corona charging is higher than that by thermal charging, but the former decays more rapidly. For the same charging method, the narrower the aluminum electrode area can lead to the lower initial surface potential, and the higher charging temperature causes the larger initial surface potential. According to the principle of corona charging and thermal charging technology it is concluded that the difference of charge storage capability between FEP and aluminum can account for the grid distribution of electric field on the FEP surface.
Polarization-insensitive and broad-angle gradient metasurface with high-efficiency anomalous reflection
Authors: Liu Tong-Jun  , Xi Xiang  , Ling Yong-Hong  , Sun Ya-Li  , Li Zhi-Wei  , Huang Li-Rong  ,   Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China;,   College of Physics Science and Technology, Yangzhou University, Yangzhou 225002, China
Published: December 2020

Polarization-insensitive metasurfaces are of great value in practical applications. In this paper, we present a polarization-insensitive reflective phase-gradient metasurface operating in optical communication band which has almost the same electromagnetic (EM) responses for both x-and y-polarized incident waves with high-efficiency anomalous reflection.The reflective metasurface employs a typical metal (Au)-insulator (SiO2)-metal (Au) structure, in which the top metal layer consists of periodic arrays of isotropic cross-shaped gold antennas, i.e. unit cells. The supercell of the metasurface is composed of five unit cells with their dimensions different from each other. The normally incident waves are reflected by the metal-grounded plane, but the reflection phases of both x-and y-polarized waves are controlled by changing the dimensions of their unit cells. Based on the finite-difference time-domain simulations, we investigate the polarization-dependent EM responses of this metasurface under the illumination of linearly polarized incident plane waves. Selecting carefully five cross-shaped gold antennas in different dimensions, we obtain polarization-insensitive metasurface with high-performance anomalous reflection in optical communication band.First, in order to investigate the polarization sensitivity of the proposed metasurface, we study the EM responses for x-and y-polarized incident waves, since arbitrary linearly-polarized EM waves can be separated into two orthogonally-polarized components. We find that the two orthogonally-polarized incident EM waves have almost the same phase and amplitude response with the phase nearly linearly changing from 0 to 2up within a supercell, hence a constant gradient of phase discontinuity is introduced and anomalous reflection will occur. We further analyze the reflected electric-field patterns and the far-field intensity distributions, from which we find that the reflected beams exhibit low-distortion wavefronts and the scattered light is predominantly reflected into the anomalous mode. As a consequence, high-efficiency anomalous reflection is realized, with a 70% reflectivity at the operating wavelength of 1480 nm. Furthermore, we look into the incident-angle dependence of the proposed metasurface, and find that the designed metasurface can exhibit polarization insensitivity within a broad incident angle ranging from -30 to 0.In conclusion, we propose a broad-angle polarization-insensitive reflective gradient metasurface with high-efficiency anomalous reflection, which has potential applications in optical communications, signal processing, displaying, imaging and other fields.
Ultrasound imaging algorithm based on generalized sidelobe canceller
Authors: Wang Ping  , Cheng Na  , Gong Zhi-Hui  , Wang Lin-Hong  ,   State Key Lab. of Power Transmission Equip. & System Security and New Tech., Chongqing University, Chongqing 400044, China
Published: December 2020

The traditional delay and sum (DAS) algorithm is the most widely adopted method in medical ultrasound imaging; although it can produce images quickly, it sacrifices the resolution and the contrast ratio. The adaptive method such as the minimum variance (MV) continuously updates the apodization weighting vectors according to the received signals, so that the variance of the weighted signals is minimized, and thus the quality of the ultrasound imaging can be improved, especially its resolution. Although the image quality may be improved in the contrast ratio as well as the resolution after combining the minimum variance with the coherence factor (MV-CF), it complicates the algorithm, and the robustness against noise is enhanced but a little. An improved ultrasound imaging algorithm based on the generalized side lobe canceller (GSC) is proposed, which is constructed according to the minimum variance principle. The canceller is designed to classify the signal into desired and noise signals, combined with wiping off the big interferential eigenvectors, so that the robustness against noise can be enhanced. Firstly, the canceller divides the weighting vector into non-adaptive and adaptive weights, then the eigenstructure subspace is established according to the covariance matrix of the received signals, and the renewed weighting vector is achieved finally by projecting the weighting vector into the left singular space of the eigenstructure subspace. Simulations of the point targets and the cyst phantom through the simulation tool Field II demonstrate that the ultrasound image acquired through the proposed method is better than the traditional DAS and MV-CF algorithms in terms of the contrast ratio and resolution. In practice, the contrast ratio increases by roughly 7 dB compared to DAS and 5 dB to MV-CF. Furthermore, the proposed method gives a more satisfactory lateral resolution as well as the lowest side lobe peak level. From the sound-absorbing speckle simulation, the contrast ratio increases by 3 dB more than that of DAS and over 4 dB than that of MV-CF when noise exists. In addition, MV-CF performs the worst in the robustness aspect while the proposed GSC method makes improvement on the basis of it. Besides, the image quality can be further improved by combining the proposed method with sign coherence factor (GSC-SCF). After such a combination, the noise added to the data sets is almost invisible in point targets simulation. It also possesses the maximum mean power in cyst region in sound-absorbing speckle simulation. Finally, an experiment is conducted on the basis of the complete data sets which are offered by the University of Michigan. Results indicate that the proposed methods can perform better than the conventional DAS and MV-CF in resolution, contrast ratio and the robustness against noise.
Three dimensional Born geometrical factor of multi-component induction logging in anisotropic media
Authors: Wang Lei  , Fan Yi-Ren  , Huang Rui  , Han Yu-Jiao  , Wu Zhen-Guan  , Xing Dong-Hui  , Li Wei  ,   School of Geosciences in China University of Petroleum, Qingdao 266580, China;,   CNPC Key Laboratory for Well Logging in China University of Petroleum, Qingdao 266580, China;,   China National Oil and Gas Exploration and development Corporation, Beijing 100034, China;,   China Oilfield Services Limited Geophysical, Tianjin 300451, China
Published: December 2020

Geometrical factor has been widely used in the design of induction tool and analysis of complex logging responses, as well as the high resolution processing of logging data. Works in this area are usually limited to two-dimensional isotropic medium and are only available to cases of coaxial transmitter and coaxial receiver coupling. For a more thorough understanding of multicomponent induction logging in the presence of transverse anisotropy, a knowledge of anisotropic geometrical factor is often necessary. In this paper, the two-dimensional and isotropic geometrical factors are extended to the anisotropic media using Born approximation, and the expressions of 3D Born geometrical factors for multicomponent induction logging are derived. Then the sensitivity and detectability of coaxial, coplanar and cross-coupling measurements are investigated. Numerical results show that with increasing coefficients of conductivity anisotropy, the spatial distribution of geometrical factors becomes increasingly complicated, and more sensitivity information can be detected by multicomponent induction tools. The multicomponent induction tool is sensitive to conductivity anisotropy at arbitrary dipping angles. In vertical wells, coplanar measurements are significantly affected by the conductivity anisotropy. Compared with coaxial and coplanar measurements, cross-coupling component offers superior sensitivity information to the conductivity anisotropy with the dipping angle being 40～ 60°. In horizontal wells, coaxial measurements are the most sensitive to the conductivity anisotropy. The extended 3D Born geometrical factor directly exhibits the anisotropy sensitivity in terms of spatial contribution, and has made up for the shortage of previous geometrical factors. The new geometrical factor will create favorable conditions for the development of new multicomponent induction tool and the interpretation of anisotropic formations.
Fractal and statistical properties of the geometrical structure of natural pores within plasma sprayed coatings
Authors: Chen Shu-Ying  , Wang Hai-Dou  , Ma Guo-Zheng  , Kang Jia-Jie  , Xu Bin-Shi  ,   National Key Laboratory for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072, China;,   School of Engineering and Technology, China University of Geosciences, Beijing 100083, China
Published: December 2020

Pores, which have remarkable influence on many properties of coatings such as wear resistance, anti-corrosion, thermostability, etc. are the natural structure formed in plasma sprayed coatings, and have been regarded as one of the most important indexes in spraying parameter refining. Hence, it is of great significance to comprehensively characterize the structural parameters of pores in the coatings, especially for the accurate evaluation of the coating quality. In this paper, probability statistics method, fractal method and digital image analysis technique are used to investigate the number, shape, size and distribution of the pores. Besides, the formation mechanism of the coatings is discussed. First, Fe-based coatings with different porous structures are fabricated at different spraying powers. Second, the digital image analysis technique is used to process the scanning electron microscope micrographs of coatings with different pores. Finally, the Weibull statistical model is utilized to analyze the distribution law of perimeter and area of the pores. The power law of area-perimeter which originats from fractal theory is employed to quantitatively characterize the irregular morphology of the pores. In order to investigate the formation mechanism of the pores, the Spraywatch is used to monitor the flying condition of the spraying particles in the whole experimental process. The result shows that fractal dimension (FD) can characterize the irregular morphology of pores. The area becomes bigger and the border becomes more complex when the FD is larger, and there is a good relationship between FD and the formation mechanism of the pores. Besides, the areas and perimeters of the pores obey the binomial Weibull distribution obviously, namely, the shape parameter (β) turns larger as pore size becomes smaller. The spraying power has a different effect on the distribution law of pore size. With the increase of the spraying power, the molten state is improved. As a result, the size of the pore decreases obviously. When the area or the perimeter is less than their corresponding characteristic values, the probability density of the pores with the same area or perimeter becomes closer to each other, which indicates that the effect of spraying power on the pores of small size is much lower.
Absolute calibration of an analog InSb detector based on multimode spatial correlation of correlated photons
Authors: Xia Mao-Peng  , Li Jian-Jun  , Gao Dong-Yang  , Hu You-Bo  , Sheng Wen-Yang  , Pang Wei-Wei  , Zheng Xiao-Bing  ,   Key Laboratory of General Optical Calibration and Characterization Technology of Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

Absolute calibration can be realized by means of correlation photon which is generated by the parametric down conversion. The main difficulty lies in obtaining correlation information about photon flux when this method is applied to analog detector calibration process. A novel method of processing the photocurrent on the basis of detecting multimode spatial correlation is proposed. By converting the charge quantity contained in the photocurrent detected in a certain time interval into the photon counting, and by using double channels balance detection and measuring mean photon counts of each model to correct the dual channels fluctuations, the high accuracy calibration of quantum efficiency can be achieved. The photon fluxes of two channels are balanced by inserting an adjustable attenuator in one optical path. The cross section of pumping beam is comparable to the detection area to ensure three-wave colinearity, and the coherent area of the correlation photons is obtained by measuring pump beam waist and lens focus length. With the known detection area, coherence time and coherence area, the average photon number of each mode is computed. This process should be performed under the average photon number of each mode as a reference which could be used for the proportional scaling of equivalent photons of two channels. Based on this new approach, the absolute power responsivity of an InSb detector is calibrated at 3390 nm with correlated photon pairs at 631 and 3390 nm. The calibration procedure and experiments are described and the uncertainty of this method is analyzed. The results show a relative combination uncertainty of about 7.785% for this calibration method, which agrees well with the result independently obtained in the national photoelectronic metrology laboratory within a relative difference of about 3.6%. This result verifies that the quantum efficiency of an analog detector can be calibrated by the correlated photon method, which has potential applications in highly accurate radiometric calibration without external standards.
Three-dimensional photoacoustic imaging technique based on acoustic lens
Authors: Zhang Yu  , Tang Zhi-Lie  , Wu Yong-Bo  , Shu Gang  ,   School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China;,   School of Electronic Engineering, South China Agriculture University, Guangzhou 510642, China;,   School of Animal Science, South China Agriculture University, Guangzhou 510642, China
Published: December 2020

Reconstruction of a sample photoacoutic (PA) image is the research focus in PA imaging system that is based on acoustic lens. Among all existing reconstruction methods, the reconstructing PA image is usually obtained by the projection of the absorption distribution which is regarded as PA signal of a sample. However, this equivalent relationship is just approximate and not accurate in theory. In this paper, the accurate relationship between the absorption coefficients of the sample placed on the object plane and its PA pressure signals focused on the image plane is successfully demonstrated. Both the integral and the extraction envelope methods are firstly proposed to reconstruct the axial PA image of an absorbent sample. The resolution of the reconstructed PA image obtained by Hilbert transform is theoretically higher than that by integral method, and the reason is explained. Different samples are chosen to experiment on the acoustic lens PA imaging system. A three-dimensional fast PA imaging of the absorbent sample is realized by combining its axial imaging capability with its lateral imaging capability of acoustic lens. The reconstruction result shows that both the lateral and the axial resolutions of the reconstruction image are both about 1 mm. The quality of a sample PA image obtained by Hilbert transform is better than that by integral method.
Ptychographic iterative engine with the incoherent illumination
Authors: Yu Wei  , He Xiao-Liang  , Liu-Cheng  , Zhu Jian-Qiang  ,   School of Science, Jiangnan University, Wuxi 214122, China;,   Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Published: December 2020

Ptychographic iterative engine (PIE) is an ideal phase microscopic method for imaging with short wavelength including X-ray and electron beam. The traditional PIE algorithm requires a purely coherent illumination. Since the coherencies of X-ray and electron beam are always much lower than coherency of the laser, it is greatly important to develop new algorithm for enhancing the capability of PIE in handling the incoherence of the illumination. A method, named polyCDI (coherent diffraction imaging), which can generate clear reconstruction with the illumination of partial coherency, was proposed recently, however due to the use of tiny pinhole in the data acquisition the view field of the reconstructed image is limited. The polyPIE algorithm, which combines the principles of polyCDI with PIE, can realize the imaging of large object with partially coherent illumination. In this paper, an improved polyPIE algorithm is developed to realize the high-resolution phase imaging under incoherent illumination by bringing the shape of the illuminating pinhole and the spectral distribution of the light source into the iterative computation. The image of the object and the illuminating probe are reconstructed for each spectral component, and the shape of the pinhole forming the illumination is used as the same spatial constraint for all the reconstructed probes on the pinhole plane. With this method a very high convergence speed and reconstruction accuracy as well as a wide view field can be achieved. This method can find many applications in the imaging with X-ray and electron beam, which are of low coherence in most of cases. The influence of the spectral width on reconstruction accuracy is also analyzed by imaging the object with illuminations of different spectral widths. It is found that the improved polyPIE algorithm can accurately reconstruct the phase and modulus images of the object when the width of the incoherent illuminating source is smaller than 10% of the central wavelength, otherwise, the convergence speed and reconstruction accuracy will become remarkably lower. By bringing the shape of the pinhole into the iterative computation, the relevance of the reconstructed illuminating probes of different spectral components is used and accordingly the reconstruction speed can be obviously accelerated. The feasibility of this suggested method is verified by a series of numerical simulations.
Superluminal and slow light of high-order harmonic for rectangle signal in erbium-doped fiber
Authors: Wang Fu  , Wang Zhi  , Wu Chong-Qing  , Liu Guo-Dong  , Mao Ya-Ya  , Sun Zhen-Chao  , Li Qiang  ,   Key Laboratory of Education Ministry on Luminescence and Optical Information Technology, Institute of Optical Information, School of Science, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

The slow light technology of the rectangle signal propagating in erbium-doped fiber (EDF) has potential applications in the fields of all optical communication and optical fiber sensing. The method of using harmonics fractional delay to evaluate the slow/fast light of rectangle signal propagating in the EDF is proposed, and the characteristics of phase delay for fundamental and high order harmonics components are analyzed for the first time based on the rate equations and the theory of the coherent population oscillations (CPO). We experimentally demonstrate the dependences of fundamental fractional delay on input power and optical gain. The maximum fractional delay 20% is obtained when the input power is about 8 mW without pump. The negative fractional delay-20% is also achieved and it will increase with the rising of the optical gain. The Nth-order fractional delays (N=1, 3, 5, 7) of rectangle signal propagating in EDF without pump are investigated. Their maximum fractional delays are all about 0.07 and the corresponding fundamental modulation frequencies are 22, 7, 5 and 3 Hz, respectively. What is more, the Nth-order fractional delays (N=1, 3, 5, 7) with pump are also investigated. Their maximum fractional delays are all about-0.135 and the corresponding fundamental modulation frequencies are 175, 58, 35 and 25 Hz, respectively. The experiments indicate that the maximum Nth-order fractional delays are equal and they will be achieved at the frequency f/N (the fundamental harmonic fractional delay is maximum at the modulation frequency f). The results show good agreement with CPO and the frequency is also located in the spectral burning hole.
Localized surface plasmon resonance modes in Ag nanowires with pentagonal cross sections
Authors: Xu Tian-Ning  , Li Xiang  , Jia Wen-Wang  , Sui Cheng-Hua  , Wu Hui-Zhen  ,   Zhijiang College of Zhejiang University of Technology, Hangzhou 310024, China;,   State Key Laboratory of Silicon Materials, Department of Physics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Ag nanowires have attracted much attention due to their potential applications in spontaneous emission amplifiers, logic gates, single photon sources, and biomolecule detection. Single crystal Ag nanowires are prepared by chemical method. The Ag nanowires exhibit pentagonal cross sections with an average radius of 80 nm. Two enhanced emission peaks (345 and 383 nm) are observed in ZnO quantum dots when mixing with Ag nanowires. To explore the origination of the enhancement, the localized surface plasmon resonance modes of Ag nanowires are investigated theoretically by the finite difference time domain method. The extinction spectrum, electric field distribution and electric field enhancement factor versus excitation wavelength of Ag nanowires are simulated. The results show that the Ag nanowires have two extinction peaks in the ultraviolet region: the 340 nm peak originating from the transverse dipole resonance (DR) and the 375 nm peak belonging to the transverse quadrupole resonance (QR). The same extinction peaks are also observed in the experimental measurement, which are consistent with the emission enhancement peaks of ZnO quantum dots. Compared with that of the DR peak, the red shift of the QR peak becomes more obvious with the increase of Ag nanowire radius. The resonance mode of the extinction peak depends on the cross sectional shape of the Ag nanowire. In the case of the traditional Ag nanowire with circular cross section, DR is excited by long wavelength light while QR is excited by short wavelength light. According to the curves of electric field enhancement factor vs excitation wavelength, the maximum enhanced electric field is observed at the apex of the pentagonal section of Ag nanowire, and the enhancement factor reaches 180 times for excitation wavelength of 377 nm. However, the electric field at the pentagon edge is enhanced only by several times. The simulation results give a reasonable explanation to the emission enhancement in Ag nanowire/ZnO quantum dot system, and indicate that Ag nanowires can be applied to improving the luminescent efficiency of semiconductor materials, biological detection, etc.
Manipulation of Hund's rule coupling and orbital-selective Mott transition
Authors: Sun Jian  , Liu Yang  , Song Yun  ,   Department of Physics, Beijing Normal University, Beijing 100875, China
Published: December 2020

Using the dynamical mean field theory with Lanczos method as its impurity solver, we study the orbital-selective Mott transition (OSMT) in the two-orbital J model and Jz model. In the multi-orbital systems, the Mott metal-insulator transition occurs successively when the widths of the bands are different. As the narrow orbital becomes Mott insulator while the wide orbital is still in metallic phase, we find an orbital-selective Mott phase (OSMP). There are two different Hubbard models that are frequently used to describe the OSMT, which are named J model and Jz model, respectively. The J Model is composed of the whole Hund's rule coupling terms, including the spin-flip term, the pair-hopping term and the Ising type Hund's rule coupling term. However, there is only Ising type Hund's rule coupling term in the Jz model.#br#We study the ratio of bandwidth W2/W1 on the OSMT by analyzing the results of the density of states and quasi-particle weight. Comparing the phase diagrams obtained from the J and Jz models with the Hund's rule coupling J(Jz)=U/4, we find that the OSMP region of the J model is much larger than that of the Jz model when W2/W1=0.5 or W2/W1=0.2. When the ratio of bandwidth increases to W2/W1=0.8, the OSMP disappears completely in the Jz model. However in the J model, we can still find the OSMT but the area of the OSMP shrinks significantly. Therefore, the OSMT happens more easily in the J model than in the Jz model.#br#In order to discuss the cooperative effect of the bandwidth and Hund's rule coupling on the OSMT, we compare the phase diagrams for different Hund's rule couplings J(Jz)=U/4 and J(Jz)=U/2. We find that when the bandwidth W2/W1≥q 0.7, the OSMT disappears in Jz model in the case of either Jz=U/4 or Jz=U/2. However, the OSMP always exists in the J model if the bandwidths of the two orbitals are different, suggesting that the rotation invariances of the Hund's rule couplings can protect the OSMP. Therefore, one should be more careful when using the Jz model instead of the J model to study the OSMP.
Effect of BaFe12O19 nanoparticles doped on the properties of single domain GdBa2Cu3O7-δ high-temperature superconductors
Authors: Zhang Xiao-Juan  , Zhang Yu-Feng  , Peng Li-Qi  , Zhou Wen-Li  , Xu Yan  , Zhou Di-Fan  , Izumi Mitsuru  ,   Department of Mathematics and Physics, Shanghai University of Electric, Shanghai 201300, China;,   Laboratory of Applied Physics, Tokyo University of Marine Science and Technology, Tokyo 135-8533, Japan
Published: December 2020

The flux pinning performance of the superconductor is important for the applications of the GdBa2Cu3O7-δ superconductor bulk. To introduce the suitable secondary phase into the GdBa2Cu3O7-δ matrix is an important way to enhance the performance of flux pinning. By using top-seeded melt texture growth process, single domain GdBa2Cu3O7-δ superconductor bulks (20 mm in diameter) doping with different quantities of BaFe12O19 nano-particles (12O19(x=0, 0.2 mol%, 0.4 mol%, 0.8 mol%)+ 10 wt% Ag2O+ 0.5 wt% Pt. The effects of different quantities of BaFe12O19 nano-particles on superconducting properties and microstructure are also investigated. The result shows that the critical current density, JC, with 0.2 mol% BaFe12O19 additions reaches a maximum value in the zero field, which is about 5.5 × 104 A/cm2. And the critical current density JC, almost increases in the whole field compared with those of the undoped bulks. The microstructure and chemical composition of GdBa2Cu3O7-δ bulk with BaFe12O19 nano-particles are implemented by the SEM-EDS technique. It is found that BaFe12O19 nano-particles keeps a similar form to that of the precursor in the final superconductor bulk. The average size of Gd2BaCuO5 particles is reduced from 1.4 μm in the undoped bulk to 0.79 μm in the bulk with 0.2 mol% BaFe12O19 nano-particles. We suggest that BaFe12O19 nano-particles may form effective magnetic flux centers in the bulks, which affects the homogeneous distribution and refinement of Gd2BaCuO5 particles. Therefore, the improvements in the critical current density and the trapped field are observed in the GdBa2Cu3O7-δ bulk with low-level doped content. The superconducting transition temperature TC, can be maintained at around 92.5 K. However, with the addition of 0.4 mol% BaFe12O19 nano-particles, the critical current density and superconducting transition temperature decrease obviously. It indicates that the excessive addition of BaFe12O19 nano-particles may affect the superconductivity properties to reduce the critical current density, JC. The result indicates that the low-level content BaFe12O19 nano-particles can be an effective second phase for the improvement of the GdBa2Cu3O7-δ superconductor bulks, which is very important for the further enhancing the superconducting properties of GdBa2Cu3O7-δ bulks by introducing the flux pinning of nano-particles.
Effects of bimodal random crystal field on the magnetization and phase transition of Blume-Capel model on nanotube
Authors: Li Xiao-Jie  , Liu Zhong-Qiang  , Wang Chun-Yang  , Xu Yu-Liang  , Kong Xiang-Mu  ,   Shandong Provincial Key Laboratory of Laser Polarization and Information Technology, Department of Physics, Qufu Normal University, Qufu 273165, China
Published: December 2020

Recently, the physical properties and applications of the magnetic nanotube have attracted a great deal of theoretical and experimental attention. The magnetization and phase transition of spin-1 Blume-Capel model on a cylindrical Ising nanotube with bimodal random crystal fields are investigated by using the effective field theory. Employing numerical calculations, we obtain the phase diagrams and the magnetization, which depend on the temperature and the parameters of random crystal fields. Our obtained results are as follows. (i) Changing the probability (p) and the ratio of the crystal fields (), the bimodal random crystal fields may describe different doped atoms acting on spins. Especially, for p = 0.5, choosing = 0,-1.0,-0.5 and 0.5, the bimodal random crystal fields can respectively degrade four typical distributions of random crystal fields, i. e., the distribution of diluted crystal fields, the distribution of symmetry staggered crystal fields, the distribution of non-symmetry staggered crystal fields, and the distribution of same-direction crystal field. (ii) The system exhibits different magnetic properties and phase transition behaviors in the diluted, staggered and same-direction crystal field. The diluted and staggered crystal fields may reduce the magnetization of the system, resulting in the ground state saturation value of magnetization, which is less than 1, while the same-direction crystal fields cannot result in a similar behavior. (iii) The system shows several phase transition temperatures, i.e., first-order and second-order phase transitions and reentrant phenomenon as the parameters of bimodal random crystal fields change. The tricritical point and reentrant phenomenon do exist for certain values of the probability, the negative crystal field and the ratio of the crystal fields in the system. The relevant experiment is needed to verify the above-mentioned theoretical results.
Influence of Mo capping layer on magnetic anisotropy of MgO/CoFeB/Mo
Authors: Yu Tao  , Liu Yi  , Zhu Zheng-Yong  , Zhong Hui-Cai  , Zhu Kai-Gui  , Gou Cheng-Ling  ,   School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China;,   Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China
Published: December 2020

In this paper, the influence of Mo capping layer on magnetic anisotropy of MgO/CoFeB/Mo with varying thickness is studied. It is found that Mo capping layer shows more saturated magnetic moments than Ta capping layer. The direction of the external magnetic field has a great influence on the magnetic anisotropy. The MgO/CoFeB/Mo sample prepared in an applied magnetic field parallel to the plane shows in-plane magnetic anisotropy (IMA). IMA becomes weak as the CoFeB thickness decreases, and it still exists when the thickness decreases to 1.1 nm. At the same time, the saturation field vertical to the plane decreases. When the thickness of CoFeB layer decreases to 0.9 nm or less, the IMA disappears. In our study, the saturated magnetization and magnetic dead layer are 1600 emu/cm3 and 0.26 nm at the annealing temperature 200 ℃, and the interface anisotropy is 0.91 erg/cm2, which is smaller than previous research results. Increasing the annealing temperature helps the sample keep the saturated state under a small magnetic field vertical to the plane, and makes IMA weak and transform into PMA. The variation of the Mo capping layer thickness affects the saturation magnetic moment of the sample. The magnetic moment shows a sharp downtrend when the Mo layer is between 1.2 and 1.6 nm, then it turns stabler with Mo capping layer thickening. Meanwhile, when the Mo capping layer is 1.6 nm, the external vertical saturation field becomes smallest. However under the parallel magnetic field, changing the thickness or annealing temperature, or changing both leads to no PMA occurring. When the magnetic field direction changes from parallel to vertical direction, some of the samples show PMA after the annealing process. The magnetic anisotropy of MgO/CoFeB/Mo varies with the thickness of Mo capping layer. IMA is present when the Mo capping layer is 1 nm or less while PMA is present when the Mo capping layer is between 1.2 and 5 nm. The sample coercive force in the vertical direction varies with thickness, and its magnetic hysteresis loss is much larger when the thickness of Mo capping layer is 1.4 nm.
Controlling of magnetic vortex chirality and polarity by spin-polarized current
Authors: Sun Ming-Juan  , Liu Yao-Wen  ,   School of Physical Science and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

For a nanodisk, magnetic vortex characterized by a curling magnetization is an energetically stable state. The magnetization in the center of the magnetic vortex is directed upward or downward, namely, the vortex core polarity p=+1 or p=-1 refers to up or down, respectively. The curling direction of magnetization, namely, the vortex chirality, is either counter-clockwise or clockwise. Thus, different combinations of chirality and polarity in a vortex structure demonstrate four stable magnetic states, which can be used to design a multibit memory cell. Such a multibit memory application requires the independent controlling of both the vortex chirality and vortex polarity, which has received considerable attention recently. Switching the vortex polarity has been achieved by using either a magnetic field or a current. The vortex chirality can be controlled by introducing asymmetric geometry of nanodisks. In this article, by using micromagnetic simulations, we present an effective method to simultaneously control the vortex chirality and polarity in a spin valve structure, in which the fixed spin polarizer layer is magnetized in the film plane when the free layer has a magnetic vortex configuration. The free layer is designed into a ladder shape with the right part being thicker than the left part. Our simulations indicate that a combination of desirable vortex chirality and polarity can be easily controlled by a Gaussian current pulse with proper strength and pulse duration through the spin-transfer torque effect. The insight into physical mechanism of the controllable vortex is demonstrated by a series of snapshots. If the magnetic moment of the free layer is saturated in the direction of 0θ θ is the angle between the magnetization and+x axis, the vortex with the counter-clockwise chirality will be generated after the pulse. In contrast, if the free layer magnetization is saturated along the direction πθ <2π, after the pulse, the vortex will have the clockwise chirality. The core polarity of the remanent vortex state is determined by the sign of the magnetic charges which are formed in the step-side of nanodisk during the current pulse.