bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulse duration effect on photoelectron spectrum of atom irradiated by strong high frequency laser
Authors: Guo Jing  , Guo Fu-Ming  , Chen Ji-Gen  , Yang Yu-Jun  ,   Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China;,   Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy(Jilin University), Changchun 130012, China;,   Department of Physics and Materials Engineering, College of Physics and Electronic Engineering, Taizhou University, Taizhou 318000, China
Published: December 2020

With the development of high harmonic generation and the free electron laser,one can obtain the laser pulses whose frequencies range from XUV to X ray.Using these novel light sources,one can investigate the electron dynamics with attosecond resolution.With the increase of intensity,a lot of nonlinear processes have been found,such as high harmonic generation, above threshold ionization and dynamic stabilization of atomic ionization.When the atom is irradiated by an ultra-intense short laser pulse,many additional sub-peaks appear in the original photoelectron peaks.The original peaks of the photoelectron spectra are formed by the ionization interference from different optical cycles.The formation of sub-peaks are attributed to the shift energy level by the action of strong laser electric field.In previous studies,the sub-peak phenomenon was mainly observed in the short pulse.In this work,we investigate the duration effect of laser pulse on this phenomenon.The photoelectron is calculated from the time-dependent wavefunction in momentum by using generalized time dependent pseudo spectral scheme.At small laser intensity,there is only main photoelectron peak near the position whose energy is the difference between the central frequency of the laser and ionization energy.As the laser duration decreases,the width of the photoelectron peak gradually increases.For the higher laser intensity,many sub-peaks appear in the photoelectron spectra.The width of the sub-peak is also decreasing with the increase of the laser pulse's duration. The amplitude of these sub-peaks is decreasing with the increasing of the duration of laser pulse.For the longer pulse (50 optical cycles),these sub-peaks disappear.The variation of the amplitude and energy position for the first sub-peak with the laser intensity is analyzed.As the increase of laser pulse width,the energy of the sub-peak increased.Comparing with the longer pulse,the short pulse has a larger enhancement.In order to understand the profiles of the photoelectron spectra,we investigate the time-dependent ionization profile of the atom.The results show that the ionization occurs in the whole duration of the laser pulse for small incident intensity.The ionization mainly occurs at the raising edge of the laser pulse for the large laser intensity.For the longer pulse,the gradient of laser intensity is small.Its energy level shift effects on the ground state of the atom is small.Thus, one can not observe any sub-peak in the photoelectron spectrum of atom irradiated by the long laser pulse.
Broadband Rydberg atom-based radio-frequency field sensor
Authors: Jiao Yue-Chun  , Zhao Jian-Ming  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Significant progress has been made in atom-based measurements of length, time, gravity and electromagnetic fields in recently years. Rydberg atom-based microwave electric field measurement, using electromagnetically induced transparency (EIT) in room temperature alkali-metal vapors, has been extensively investigated and aroused the broad interest. This approach may establish a new standard for the measurements of microwave (MW) and radio frequency (RF) electric fields.In this review, we describe the work on a new method of measuring electric fields based on quantum interference by using either cesium or rubidium atoms contained in a dielectric vapor cell. Rydberg atoms with principal quantum number n >>1 have large direct current (DC) polarizabilities and microwave transition dipole moments, thereby making them extremely sensitive to external electric fields. Using the Rydberg three-level EIT to detect the level splitting and shift that is induced by the external field, we can realize a rapid and robust self-calibration method of measuring the electric field in a frequency range from 0.01 GHz to 1000 GHz. For the MW electric field (frequency range > 1 GHz), the MW field causes the Rydberg states to split, known as an Autler-Townes splitting (A-T) effect when the applied microwave can resonate with adjacent Rydberg states. The MW coupled A-T splitting is proportional to the applied electric field strength, from which the field strength is measured. Using the EIT window, a high sensitivity of 3 μV·cm-1·Hz-1/2 and small electric field of 1 μV/cm are expected to be achieved with a modest setup, and the limitations of the sensitivity are also addressed in the review. For the RF field at frequency mj EIT lines, and avoided crossings formed with the fine-structure levels of equal mj and different J's, which is used to calibrate and measure the RF field amplitude. On the other hand, the dependence of the EIT-line strength on the RF field polarization provides a fast and robust polarization measurement of RF fields based on matching experimental data with a theoretical simulation. The measurements of minimum strengths and sensitivity of RF fields based on Rydberg atoms are one order magnitude below the values obtained by traditional antenna methods. The atom-based field measurement paves the way for determining fields through calibration-free, invariable atomic properties and miniaturization. We also propose its various potential applications in the future.
Principle and noise performance of optical phase arithmetic devices using four wave mixing
Authors: Cao Ya-Min  , Wu Bao-Jian  , Wan Feng  , Qiu Kun  ,   Key Laboratory of Optical Fiber Sensing and Communication, Ministry of Education, School of Communication and Information Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

The existing theoretical equations cannot provide an excellent guidance for developing four-wave mixing (FWM)-based optical logic devices, though the experiments have been done in several researches. The optimization of noise figure performances of such devices should be further investigated. In the paper, the universal analytic expressions for the amplitude and phase of the idler in degenerate or non-degenerate FWM process under pump depletion are derived in detail from the nonlinear coupled-mode equations for guiding optical waves propagation in highly nonlinear fiber. The universal analytic expressions are obtained by the first-and the third-kind of elliptic integrals. By using equivalent infinitesimal to calculate the limit of phase sensitive amplification, we find out the initial phase relationship between the idler and the input guided wave for phase-independent amplification, which is crucially important for explaining the operating principles of the FWM-based adder and subtracter. As an example, the configuration of non-degenerate FWM-based hybrid arithmetic device with three logic functions of A+B-C, A+C-B, and B+C-A for QPSK signals is presented, and then the noise transfer characteristics in terms of signal-to-noise ratio (SNR) and error vector magnitude (EVM) are taken into account by adjusting the fiber length, input wavelength, and optical power. The calculation results show as follows. 1) This kind of arithmetic device has a noise figure of about 1.1 dB and an input SNR of more than 24 dB is necessary for the symbol error rate of 10-3 without forward error correction, corresponding to an output EVM of 23.2%. 2) The length of highly nonlinear fiber used in the hybrid arithmetic device may be taken flexibly, provided that the variation of FWM conversion efficiency is controlled in a range of 1 dB relative to the maximum, with an EVM fluctuation of less than for the idlers. 3) The hybrid arithmetic device has an operating optical bandwidth of about 16 nm for the SNR degradation of 1.3 dB. 4) The output EVM increases with the increase of input power, and the allowable input power should be no more than 100 mW for an input SNR of 28 dB, noting that the larger the input SNR, the higher the allowable input power is.
Simulink modeling of memristor, memcapacitor, meminductor and their characteristics analysis
Authors: Wang Xiao-Yuan  , Yu Jun  , Wang Guang-Yi  ,   Institute of Modern Circuits and Intelligent Information, Hangzhou Dianzi University, Hangzhou 310018, China
Published: December 2020

Memristor, memcapacitor and meminductor are novel nonlinear circuit elements with memory, which are also known as the memory elements. Based on the mathematical models of these three circuit elements, from the point of view of mathematical analysis, memristor, memcapacitor and meminductor Simulink based models are established. Simulink models of the memory elements reflect that their values are dependent on their historical states and their state variables, and correctly show their unique memory properties. A series of simulation analyses are done, and the typical characteristics of the three memory elements are obtained, showing the validities of these models. In addition, by studying the circuit characteristics under different parameters and excitations, the changing laws of these equivalent models with frequency and amplitude are obtained, which lay the foundation for research and application based on memristor, memcapacitor and meminductor's Simulink simulator.
Binding process between E.coli SSB and ssDNA by single-molecule dynamics
Authors: Lu Yue  , Ma Jian-Bing  , Teng Cui-Juan  , Lu Ying  , Li Ming  , Xu Chun-Hua  ,   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 100049, China
Published: December 2020

Single-stranded DNA binding proteins (SSBs) widely exist in different kinds of creatures. It can bind single-stranded DNA (ssDNA) with high affinity. The binding is sequence independent. SSB can also interact with different kinds of proteins, and thus leading them to work at the special sites. It plays an essential role in cell metabolism. E.coli SSB is a representative of SSB among all kinds of SSBs, it is a homotetramer consisting of four 18.9 kD subunits, the homotetramer is stable under low concentration. E.coli SSB has different binding modes under different salt concentrations (for example NaCl). When NaCl concentration is higher than 200 mM, E.coli SSB can bind 65 nt ssDNA, when NaCl concentration is lower than 20 mM, it can bind 35 nt ssDNA, and when the NaCl concentration is between 20 mM and 200 mM, it can bind 56 nt ssDNA. The characteristics of E.coli SSB are so attractive that a large number of researches have been done to distinguish its binding process. Earlier researchers tried to use stop flow technology to study the interaction between SSB and ssDNA in bulk. However, the high affinity between SSB and ssDNA makes this interaction too rapid to be observed at all, and the dissociate interaction even could not be measured. Single molecule technology which combines with low and accurate force offers researchers another way to achieve this goal. Some researchers observed the unwrapping phenomenon in an optical tweezers pulling experiment. However, they did not find the detailed process of binding or dissociation. In our work, we use a magnetic tweezer to pull the SSB/ssDNA complex and find a special phenomenon like double-state jump. Using the single molecule dynamics to analyse the data, we find that this phenomenon is the combination and dissociation between SSB and ssDNA. After comparing the pulling curve of ssDNA only and SSB/ssDNA complex, we find that the SSB binding process consists of two stages, one is rapid combination/dissociation under the action of a critical force; the other is continuous wrapping following the reduced force. According to Bell formula and SSB/ssDNA complex binding model, we obtain the interaction rate and free energy parameters under 0 pN, and we calibrate the free energy to obtain its continuous wrapping part, so we can obtain the whole free energy landscape and understand the binding process. Our analysis way is also applicable to the case of similar interactions to obtain their interaction details and free energy characteristics.
Influence of source size and spectral bandwidth on the imaging of a zone plate
Authors: Lu Zhong-Wei , Wang Xiao-Fang ,   Department of Engineering and Applied Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Direct X-ray imaging by a Fresnel zone plate (FZP) has achieved a spatial resolution of 10 nm on a synchrotron beamline. It may be used to obtain submicron-resolution X-ray images of laser-plasma sources or fusion targets. However, none of previous imaging experiments with laser-plasma kilo-elelctron-volt X-ray sources shows such a high resolution. In comparison with the FZP imaging on a synchrotron, we consider a case of imaging an extended object with a laser-plasma X-ray source that the illumination monochromaticity is lower and the field of view larger. Our simulations show that the spatial resolution is affected by both the object size and the spectral bandwidth of the source, which can explain the previous experiments. We conclude that by using a 100-zone FZP to image an object with up to 700 μm in size, a spatial resolution better than 1 μm can be realized by using X-rays of several kilo-electron volts and a spectral bandwidth just less than 3%. In this paper, we report a proof-of-principle study in simulation and experiment in an optical range centered at 632.8 nm. The simulation is performed with the same method as that previously used for X-ray imaging but with a 100-zone FZP working in the optical range. Simulations show that with the increase of the object size, the field-of-view contrast is degraded, but the spatial resolution is nearly unchanged. With the increase of the spectral bandwidth for the illumination, both the contrast and the resolution are degraded. In the experiments, different spectral bandwidths are realized by band-pass filters and different object sizes by an adjustable aperture. The experimental results are confirmed to be in agreement with the simulations. These results reveal that given a satisfied spectral bandwidth of laser-plasma X rays, the FZP imaging will be a promising approach to 1 μm or higher resolution X-ray imaging of a 1-mm-size object.
Hydrogen storage capacity of expanded sandwich structure graphene-2Li-graphene
Authors: Zhou Xiao-Feng , Fang Hao-Yu , Tang Chun-Mei ,   College of Science, Hohai Univeisity, Nanjing 210098, China
Published: December 2020

The growth of population and the limited supply of fossil fuels have forced the world to seek for new kinds of alternative energy sources which are abundant, renewable, efficient, secure and pollution-free. In this regard, hydrogen is generally considered as a potential candidate. However, it is a great challenge to find hydrogen storage materials with large hydrogen gravimetric density under ambient thermodynamic conditions. The most effective way to improve the hydrogen storage capacity is to decorate the pure nanomaterials with transition metals, alkaline metals, and alkaline earth metals. The generalized gradient approximation based on density functional theory is used to study the hydrogen storage capacity of the expanded sandwich structure graphene-2Li-graphene. It is calculated that the structure with the Li atom located above the face site of the hexagonal ring of the graphene has the maximum binding energy (1.19 eV), which is less than the experimental cohesive energy of bulk Li (1.63 eV). However, the calculated binding energy values of the Li atom to the upper and lower graphene layer are both 3.43 eV, which is much larger than the experimental cohesive energy value of bulk Li, so it can prevent the Li atoms from clustering between graphene layers. Each Li atom in the graphene-2Li-graphene structure can adsorb 3 H2 molecules at most. Thus, the hydrogen gravimetric density of graphene-2(Li-3H2)-graphene is 10.20 wt.%, which had far exceeded the gravimetric density of the target value of 5.5 wt.% by the year 2017 specified by the US Department of Energy. The average adsorption energy values of H2 adsorbed per Li are 0.37, 0.17, and 0.12 eV respectively for 1−3 H2 molecules, which are between the physical adsorption and chemical adsorption(0.1−0.8 eV), therefore, it can realize the reversible adsorption of hydrogen. Each Li atom can adsorb 3 H2 molecules at most by the electronic polarization interaction. The dynamic calculations and GFRF calculations show that the interlayer Li atom doped double-layer graphene has good reversible adsorption performance for hydrogen. This research can provide a good research idea for developing good hydrogen storage materials and theoretical basis for experimental worker. These findings can suggest a way to design hydrogen storage materials under the near-ambient conditions.
Structure and properties of nature clathrate and its application in energy and enviromental science
Authors: Zhu Jin-Long  , Zhao Yu-Sheng  , Jin Chang-Qing  ,   1. Center for High Pressure Science and Technology Advanced Research, Beijing 100094, China;,   2. Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China;,   3. Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Clathrate hydrates are energy and environmental related materials for energy storage and extraction, as well as for waste gas sequestration. The three general structures of natural clathrates, structure I, structure Ⅱ and structure H are reviewed in the aspects of stability, cage size, and preferred guest molecule encapsulation. Neutron scattering technique has its unique advantage of clathrate hydrates characterization, such as large bulk property determination, penetration of high pressure vessel and the clathrate sample inside, sensitive to light elements (clathrate hydrates mainly containing C, H, and O atoms). Neutron diffraction and inelastic neutron scattering of clathrate hydrates are covered on the abilities of H/D atoms positions and anisotropic thermal parameters, pressure-temperature-dependent guest molecule occupancy, the disordered distributions of guest molecules and the nuclear density distributions, the thermodynamic and kinetic process of formation and decomposition, the translational and rotational vibration models of guest molecules and their quantum state transitions. Using CO2 to gently replace CH4 in methane hydrate is one of the most attractive exploiting schemes for its benefits to both geologic hazard consideration and cost efficiency (energy extraction and CO2 sequestration).
Definition and quantification of hydration water in aqueous solutions
Authors: Wang Qiang  , Cao Ze-Xian  ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Water molecules in the very proximity to the solute differ a lot from those in the far and the bulk water in both structure and property, they are usually referred to as hydration water or bound water. There is no doubt about the effect of hydration water on the property and structure of solute in solution, in particular when biological macromolecules are of concern. However, by far, there are even significant controversies over the understanding of hydration water, including the accurate definition and quantification of hydration water, the quantitative evaluation of the difference in the properties between the hydration water and free water, and how the hydration water is involved in the various biological processes, etc. For resolving the aforementioned issues, it would be of essential importance to formulate a quantification scheme for the hydration water on a sound footing. In the present article, the principles of various spectrometric techniques for determining hydration water are briefly examined, and the main deficiency in quantification of hydration water for the individual techniques is analyzed. Those techniques based on the inflection point of the concentration dependence of some physical properties of the solution are also scrutinized. Finally, we present in detail a quantification scheme for hydration water based on the concentration dependence of glass transition temperature, which leads to quite a universal categorization of an aqueous solution into three distinct zones. Also the crystallization dynamics thus revealed might be helpful for understanding the water-involved processes in other circumstances.
Dynamics of A-exciton and spin relaxation in WS2 and WSe2 monolayer
Authors: Yu Yang  , Zhang Wen-Jie  , Zhao Wan-Ying  , Lin Xian  , Jin Zuan-Ming  , Liu Wei-Min  , Ma Guo-Hong  ,   1. Department of Physics, Shanghai University, Shanghai 200444, China;,   2. School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China;,   3. STU & SIOM Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, China
Published: December 2020

Two-dimensional transitional metal dichalcogenide (2D TMD) emerges as a good candidate material in optoelectronics and valleytronics due to its particular exciton effect and strong spin-valley locking. Owing to the enhancement of quantum confinement effect and the decline of dielectric shielding effect, the optical excitation of electron-hole pair is enhanced substantially, which makes large TMD exciton binding energy and makes excitons observed easily at room temperature or even higher temperature. Optical response of 2D TMD is dominated by excitons at room temperature, which provides an ideal medium for studying the generation, relaxation and interaction of excitons or trions. By employing ultrafast time resolved spectroscopy, we investigate experimentally the dynamic behaviors of A-exciton and spin relaxations for two types of TMDs, i.e. WS2 and WSe2 monolayers, respectively. By tuning the excitation wavelength of the degenerate pump and probe laser beam, the WS2 monolayer and WSe2 monolayer are excited at their A-exciton resonance transition position or near their A-exciton resonance transition position in order to compare the dynamical evolutions of band structure and exciton polarization of the two similar WS2 and WSe2 monolayer structures. Our experimental results reveal that the relaxation of A exciton in WS2 shows biexponential decay, while that of WSe2 shows triexponential decay, and the A-exciton life time in WSe2 is much longer than that of WS2 counterpart. The spin relaxation of A exciton in WS2 shows a monoexponential feature with a lifetime of 0.35 ps, which is dominated by the electron-hole exchange interaction. For the case of WSe2, the spin relaxation can be well fitted with biexponential function, the fast component has a lifetime of 0.5 ps and the slow one has a lifetime of 28 ps. The fast relaxation is dominated by the electron-hole exchange interaction, and the slow one comes from the formation of dark exciton via spin-lattice coupling. By tuning the excitation wavelength around A-exciton transition, the formation of dark exciton in WSe2 is demonstrated to be much more effective than that in WS2 monolayer. Our experimental results provide qualitative physical images for an in-depth understanding of the relationship between exciton and TMD structure, and also provide reference for further designing and regulating the TMDs based optoelectronic devices.
Design of 100-MeV proton beam spreading scheme with double-ring double scattering method
Authors: Han Jin-Hua , Guo Gang , Liu Jian-Cheng , Sui Li , Kong Fu-Quan , Xiao Shu-Yan , Qin Ying-Can , Zhang Yan-Wen ,   Department of Nuclear Physics, China Institute of Atomic Energy, National Innovation Center of Radiation Application, Beijing 102413, China
Published: December 2020

To obtain a large uniform beam field for proton single event effect (SEE) experiments, the double-ring double scattering method (DDSM) is employed for spreading the 100 MeV proton beam provided by the 100 MeV proton cyclotron at China Institute of Atomic Energy. With the Geant 4 simulations, the fundamentals of the DDSM are further explored, the achieved effect of our DDSM scheme design is presented, and the influences of some possible factors in practice on the produced beam field are discussed. We find that the the outer part of the second scatter plays an important role in enlarging the area of the uniform field and improving its uniformity. We also find that the first scatter and the inner part of the second scatter play a decisive role in determining the proton flux of the uniform area. The scattering between the spread proton beam and the accelerator tube behind the second scatter damages the uniformity and leads the energy of the produced beam field to straggle. Therefore, the tube should be made as short as possible. The size of the initial beam spot on the first scatter affects the produced beam field to some extent. The spot should be focused as much as possible in a circle with a radius of 0.5 cm. At a larger distance, a larger uniform field can be produced due to the spreading of the proton beam along the space. The decrease in the incident proton energy causes the flux and uniformity to decrease, and also leads the energy loss to increase and the energy of the produced proton beam field to straggle. Using our DDSM schematic design, the simulations show that an 8-cm-diameter beam field with a uniformity of ±1.89% can be produced at a distance of 2.4 m, thereby meeting the need for an SEE experiment of a device-level sample, and that a 20-cm-radius beam field with a uniformity of ±5.32% can be created at a distance of 5.0 m, thereby meeting the need for an SEE experiment of a system-level sample of comparable size. By taking into consideration the uniformity and energy straggling, our design is basically applicable to the protons in the 70−100 MeV energy region that the accelerator can provide directly.
An accurate inversion method of aerosol extinction coefficient about ground-based lidar without needing calibration
Authors: Liu Hou-Tong , Mao Min-Juan ,   College of Mathematics, Physics and Engineering, Anhui University of Technology, Maanshan 243002, China,   Zhejiang Meteorology Science Institute, Hangzhou 310017, China
Published: December 2020

 How to accurately calibrate the lidar data about haze in the presence of some cloud layers over the haze has always been a subject to be solved for data inversion of Mie scattering lidar. It is difficult for laser to penetrate the haze and clouds simultaneously, so the backscattering signal of lidar cannot be calibrated by using a clear air layer when the haze is under the low clouds. For the portable Mie scattering lidar with a detecting range of less than 6 km, it is also difficult to calibrate the lidar signals by using a clear air layer. An iterative algorithm for aerosol extinction coefficient is proposed based on the characteristics of the Fernald forward integral equation in this paper. By specific settings for the inversion process, the difference between the inversion value and the expected one of aerosol extinction coefficient is reduced after each iteration. After several iterations, the difference between the inversion value and the expected one of aerosol extinction coefficient is small enough to be negligible.

The disadvantage of the iterative algorithm for aerosol extinction coefficient is that the inversion results are affected by the overlap factor of lidar. The errors of lidar overlap factor measured experimentally at different times are slightly different. However, the influence about the overlap factor of lidar measured experimentally at different times on the inversion results is slightly different when the iterative algorithm for aerosol extinction coefficient is used to calculate aerosol extinction coefficient.

The results of preliminary calculation show that the iterative algorithm of aerosol extinction coefficient can accurately reproduce aerosol extinction coefficient profile without needing calibration of the lidar data. For the haze detection signal that cannot be calibrated by a clear air layer, the vertical distribution of the haze extinction coefficient can be accurately retrieved by the iterative algorithm for aerosol extinction coefficients. The vertical distribution of aerosol extinction coefficients can also be accurately retrieved by using the iterative algorithm of aerosol extinction coefficients for the Mie backscattering lidar data with the measuring height less than 6 km. Through comparative analysis and research, it is found that for the same lidar data, the aerosol extinction coefficient obtained by the iterative algorithm for aerosol extinction coefficient is closer to the actual value than that by the slope method.
Memory capacitance behavior at single resistance state in memristor and multi-state characteristic
Authors: Liu Ru-Xin , Dong Rui-Xin , Yan Xun-Ling , Xiao Xia ,   Shandong Key Laboratory of Optical Communication Science and Technology, School of Physics Science and Information Technology, Liaocheng University, Liaocheng 252059, China
Published: December 2020

With the advent of the information age, big data put forward higher requirements for capacity of storage devices. Compared with the method of reducing the size of the device to enhance the integration level, the high density storage of increasing the memory state of the single device will be very beneficial to solving the problem. In this work, we propose an idea of two-parameter and multi-state memory device involved in both resistance and capacitance operation levels. At first, a new donor-acceptor (D-A)-type copolymer is designed and synthesized. Then, the memory device of Al/copolymer/ITO structure is fabricated, and the current-voltage (I-V) and capacitance-voltage (C-V) curves are measured by a KEITHLEY 4200 semiconductor characterization system. The device not only displays the obvious memory resistance characteristics, but also has the memory capacitance behavior in single resistance state, which results in two resistance states and four capacitance states, so that the device has the capability of two-parameter and multi-state memory. In addition, the device shows more capacitance states after the switching behavior has been modulated by the voltage amplitude, which provides an effective method to control the memory states. In order to study the conductive mechanism of the device, we test the relationship between resistance and temperature. It is found that the resistance decreases with the increase of temperature, indicating that the device has the obvious semiconductor properties. Furthermore, the fitting results of I-V data show that the mechanism of resistance switching is in good consistence with the classical trap-controlled space charge limited current theory. The capacitance switching in single resistance state is closely related to the polarization characteristic of D-A structure in the copolymer film. The polarization force microscopy phase image shows that the copolymer film has obvious polarization and depolarization characteristics under the external electric field. Based on the polarization characteristics of copolymer, the correlation between memory resistance and memory capacitance is established by introducing a polarization operator of molecules, and the matrix model describing the two-parameter and multi-state memory characteristics is given. The above results show that the multi-state memory characteristics will store more information than 2-bits mode in a single cell, which will provide a reference for improving the storage density of information.
Ultrafast spin dynamics in double-magnetic-center endohedral fullerene Y2C2@C82-C2(1)
Authors: Huang Rui , Li Chun , Jin Wei , Georgios Lefkidis , Wolfgang Hübner ,   School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an 710072, China,   School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, China,   Department of Physics and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67653 Kaiserslautern, Germany
Published: December 2020

Spin switching and spin transfer are essential prerequisites for designing the spin-logic devices based on endohedral fullerenes. In this paper by combining the theoreticalΛ-process model with a self-designed genetic algorithm, we are able to theoretically observe spin-switching and spin-transfer scenarios on the subpicosecond time scale in the endohedral fullerene Y2C2@C82-C2(1) from first principles. The results show that the geometry of the optimized enclosed Y2C2 cluster is consistent with the experimental data. There exists a certain repulsive force between the external C82-C2(1) cage and the encaged cluster. However, the whole system still maintains its integral cage structure due to the excellent stability of the fullerene. In the Y2C2@C82-C2(1) system, it is found that the spin density is highly localized on the two Y atoms and only minimally distributed on the carbon cage. By analyzing the spin-density distribution and the evolution of the spin expectation values as influenced by the laser pulses, it is found that global spin switching can be achieved on the two Y atoms, while spin transfer between the two Y atoms actually results from the redistribution of the spin density among the two magnetic centers and the carbon cage under the action of the optimized laser pulses. The achieved spin-switching scenario completes within about 1000 fs and its fidelity reaches 97.8%, while the obtained spin-transfer process completes within 200 fs and its fidelity reaches 95.1%. The electron absorption spectra of the system verify that optical transitions are possible between the main intermediate states and the initial and final states involved in the spin-switching and spin-transfer scenarios. Therefore, by analyzing the electron absorption spectra corresponding to the initial and final states, the energy of the laser pulses adopted for the studied spin-dynamics process can be predicted, and the spin transferability can be evaluated. In addition, it is found that the smaller the detuning between the required energy difference and the applied laser pulse energy is, the greater the probability for spin switching/transfer scenarios becomes. The present results reveal the mechanisms of the laser-induced ultrafast spin dynamics in Y2C2@C82-C2(1) and can provide a theoretical basis for designing the spin-logic devices on realistic endohedral fullerenes.
Q-plate based dual image asymmetric polarization encryption
Authors: Xu Qi-Jun , Li De-Lin , Chang Chen-Liang , Yuan Cao-Jin , Feng Shao-Tong , Nie Shou-Ping ,   Key Laboratory for Opto-Electronic Technology of Jiangsu Province, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

With the rapid development of computer network technology, information security has drawn considerable attention in recent years. Owing to the characteristics of multi-dimensional operation and parallel processing capability, optical image encryption techniques are arousing great interest in many exciting fields. Since the pioneering work on optical image encryption using double random phase encoding technique, a large number of algorithms and architectures have been proposed and realized. However, with the further analysis of the securities of these schemes, most of them have been verified to be vulnerable to different types of attack algorithms. Recently, optical encryption schemes based on the polarization properties of light wave have been extensively studied, for an additional flexibility in the encryption key design is provided, which can achieve high robustness against brute force attack by a combination of multiple private keys. Nevertheless, optical encryption schemes based on the polarization properties of light wave could still be vulnerable to known- and chosen- plaintext attacks. Therefore, in this paper, a novel asymmetric polarization encryption method is implemented for dual images, and combined with interference-based optical image encryption method and a Q-plate. First, the information about the two images to be encrypted is separated into two pure phase plates by means of interference optical image encryption, which will be further encoded into two mutually orthogonally polarized light beams. Next, the Q-plate and pixelated polarizer are used for realizing different polarization distributions of the two light beam. Ultimately, the output intensity distribution is recorded by a charge coupled device (CCD) which will be treated as the final ciphertext. For actualizing the asymmetric encryption, one of the pure phase plates acts as a decryption key, which is different from the encryption key. We can control the polarization state of each pixel according to the parameter q, causing the Q-plate to be electrically controllable and the optic-axis orientation of each pixel to differ from one another. It should be emphasized that the value of q and the polarization angle of the pixelated polarizer play the role of two encryption keys, which improves the security of the algorithm extremely, due to their high sensitiveness. Theoretical analyses and numerical simulations verify the feasibility and effectiveness of the proposed encryption scheme.
Influence of plasma shielding effect on ground state and excited state energies of Ar16+
Authors: Ma Kun , Chen Zhan-Bin , Huang Shi-Zhong ,   School of Information Engineering, Huangshan University, Huangshan 245041, China,   School of Science, Hunan University of Technology, Zhuzhou 412007, China,   College of Physics and Electrical Information, Anhui Normal University, Wuhu 241000, China
Published: December 2020

A systematical knowledge of the atomic properties in plasma is of great interest for various research areas, such as the explanation of the X-ray radiation from universe, plasma diagnostics, extreme ultraviolet (EUV) and X-ray sources and so on. Among these researches, the detailed information about how the plasma influences the atomic energy level and transition spectrum are crucial for understanding the X-ray emission mechanism and the state of plasma. An analytic calculation method of treating the non-relativistic energy and its relativistic corrections for the multi-electron atoms embedded in weakly coupled plasma is developed based on the Rayleigh-Ritz variation method. The systematical investigations are performed for the ground state 1s2 1S, single excited states 1sns 1,2S (n = 2−5), 1snp 1,3P (n = 2−5) and double excited state 2s2p 1P of Ar16+ ion in weak coupled plasma. The analytic formulas for calculating the non-relativistic energy and its relativistic correction energy are derived, which include mass correction, one and two-body Darwin correction, spin-spin contact interaction and orbit-orbit interaction. All the angular integration spin sums involved in the problem are worked out explicitly by using the irreducible theory. The influence of plasma on non-relativistic energy and relativistic correction energy are discussed. The results show that the mass correction and the one-body Darwin correction are the main ones among the terms of relativistic correction, and are three orders of magnitude greater than the other relativistic terms. The plasma shielding effect mainly affects the non-relativistic energy, and has little effect on the relativistic correction. At the same time, it has a more significant selectivity for the electronic configuration. Further research shows that the influence of plasma on the energy of the outer shell electron is greater than that of the inner shell electron. With the increase of the plasma shielding parameters, the outer shell electron extends outward, and the higher the excited state, the greater the degree of extension is. This work should be useful for astrophysical applications where such a plasma environment exists.
Simulating Dirac, Weyl and Maxwell equations with cold atoms in optical lattices
Authors: Zhu Yan-Qing , Zhang Dan-Wei , Zhu Shi-Liang ,   National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China,   Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China
Published: December 2020

Relativistic wave equations, such as Dirac, Weyl or Maxwell equations, are fundamental equations which we use to describe the dynamics of the microscopic particles. On the other hand, recent experimental and theoretical studies have shown that almost all parameters in cold atomic systems are precisely tunable, so the cold atom systems are considered as an ideal platform to perform quantum simulations. It can be used to study some topics in high energy and condensed matter physics. In this article, we will first introduce the ideas and methods for engineering the Hamiltonian of atoms, mainly related to the theories of laser-assisted tunneling. Based on these methods, one can simulate the equations of motion of relativistic particles and observe some interesting behaviors which are hard to be observed in other systems. The article reviews these recent advances.
Manipulating longitudinal photonic spin Hall effect based on dynamic and Pancharatnam-Berry phase
Authors: Liu Jin-An , Tu Jia-Long , Lu Zhi-Li , Wu Bai-Wei , Hu Qi , Ma Hong-Hua , Chen Huan , Yi Xu-Nong ,   College of Physics and Electronic Information Engineering, Hubei Engineering University, Xiaogan 432000, China
Published: December 2020

Photonic spin Hall effect is generally described as a spin-dependent splitting. Previous studies have focused on the transverse spin-dependent splitting of light field. In this work, a method of manipulating the longitudinal photonic spin Hall effect which is based on dynamic and Pancharatnam-Berry phase is proposed. The theoretical analysis demonstrates that the lens group consisting of a Pancharatnam-Berry phase lens and a dynamic lens has two spin-dependent foci. Firstly, because Pancharatnam-Berry phase is spin-dependent, the left- and right-handed circularly polarized component can respectively acquire a Pancharatnam-Berry phase with opposite sign when a linearly polarized light beam passes through the Pancharatnam-Berry phase lens with phase retardation \begin{document}${\text{π}}$\end{document}. It leads one circularly polarized component to be focused and the other diverged. This is essentially the spin-dependent splitting of light field in momentum space, which is caused by Pancharatnam-Berry phase. And then, an ordinary lens is inserted behind the Pancharatnam-Berry phase lens to introduce a dynamic phase modulation. Due to dynamic phase being spin-independent, the constructed lens group can focus the photons with different spin states at different focal points longitudinally under the appropriate conditions. In other words, the lens group has two spin-dependent focal points. The two focal points split the photons with different spin states in the longitudinal direction. The longitudinal spin-dependent splitting is dependent on the focal lengths of the two lens and the distance between the two lenses. By changing the three parameters, arbitrary longitudinal spin-dependent splitting can be obtained. Lastly, an experimental system is set up to verify the theoretical results. The relationship between the spin-dependent splitting and the distance between the two lenses is measured. By introducing a Glan laser polarizer and a quarter wave-plate, the circularly polarized chirality of the light field at the focal point is also measured. These experimental results are all in good agreement with the theoretical analyses. These results are helpful in understanding the physical origin of photonic spin Hall effect and developing novel photonic devices based on photonic spin Hall effect.
Crystal structure and optical properties of GaAs nanowires
Authors: Wang Peng-Hua , Tang Ji-Long , Kang Yu-Bin , Fang Xuan , Fang Dan , Wang Deng-Kui , Lin Feng-Yuan , Wang Xiao-Hua , Wei Zhi-Peng ,   State Key Laboratory of High Power Semiconductor Laser, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

Gallium arsenide (GaAs) nanowires are epitaxially grown on an N-type Si (111) substrate by molecular beam epitaxy according to self-catalysis growth mechanism. Testing the grown nanowires by scanning electron microscope, it is found that the nanowires have high verticality and good uniformity in length and diameter. Variable temperature photoluminescence (PL) spectroscopy is used on nanowires. The test results show that the two luminescence peaks P1 and P2 at 10 K are located at 1.493 eV and 1.516 eV, respectively, and it is inferred that it may be the luminescence caused by WZ/ZB miscible structure and the free exciton luminescence peak. These two peaks present red-shift with temperature increasing. The temperature change curve is obtained by fitting the Varshni formula. The variable power PL spectroscopy test finds that the peak position of P1 position is blue shifted with power increasing, but the peak position of the P2 remains unchanged. By fitting, it is found that the P1 peak position is linearly related to power to the power of 1/3, and it is judged that it may be type-II luminescence caused by WZ/ZB mixed phase structure. At the same time, the peak position of the P2 position is fitted and parameter α approximately equals 1.56, therefore P2 is a free exciton luminescence. A Raman spectrum test is performed on the nanowires, and an E2 phonon peak unique to the GaAs WZ structure is found from the spectrum. It is proved that the grown nanowires possess WZ/ZB mixed phase structures, and the hybrid phase structure of nanowires is more intuitively observed by high resolution transmission electron microscopy.