通讯机构：
[Wei-Bing Zhang] H;Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering, School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha 410114, People's Republic of China
摘要：
Ferrovalley materials with spontaneous valley polarization are crucial to valleytronic application. Based on first-principles calculations, we demonstrate that two-dimensional (2D) YX2(X= I, Br, and Cl) in a 2H structure constitutes a series of promising ferrovalley semiconductors with large spontaneous valley polarization and high magnetic transition temperature. Our calculations reveal that YX2 are dynamically, energetically, thermally and mechanically stable 2D ferromagnetic semiconductors with a magnetic transition temperature about 200 K. Due to the natural noncentrosymmetric structure, intrinsic ferromagnetic order and strong spin orbital coupling, the large spontaneous valley polarizations of 108.98, 57.70, and 22.35 meV are also predicted in single-layer YX2(X = I, Br, and Cl), respectively. The anomalous valley Hall effect is also proposed based on the valley contrasting Berry curvature. Moreover, the ferromagnetism and valley polarization are found to be effectively tuning by applying a biaxial strain. Interestingly, the suppressed valley physics of YBr2 and YCl2 can be switched on via applying a moderate compression strain. The present findings promise YX2 as competitive candidates for the further experimental studies and practical applications in valleytronics.
期刊：
PHYSICAL CHEMISTRY CHEMICAL PHYSICS,2023年25(22):15271-15278 ISSN：1463-9076
通讯作者：
Wang, Yanxia;Chen, ZY
作者机构：
[Wang, Yanxia; Tang, Yu; Li, Tao; Chen, Zhaoyong; Wen, Junhao; Li, Zihua; Lin, Feng] Changsha Univ Sci & Technol, Sch Mat Sci & Engn, Changsha 410114, Peoples R China.;[Wang, Yanxia; Zhu, Huali; Chen, Zhaoyong] Changsha Univ Sci & Technol, Inst New Energy & Power Battery, Changsha 410114, Hunan, Peoples R China.;[Zhu, Huali] Changsha Univ Sci & Technol, Sch Phys & Elect Sci, Changsha 410114, Peoples R China.
通讯机构：
[Wang, YX; Chen, ZY ] C;Changsha Univ Sci & Technol, Sch Mat Sci & Engn, Changsha 410114, Peoples R China.;Changsha Univ Sci & Technol, Inst New Energy & Power Battery, Changsha 410114, Hunan, Peoples R China.
摘要：
Li-rich Mn-based layered materials are considered the most promising next-generation high-energy-density cathode materials due to their high capacity, but their large irreversible capacity loss and severe voltage attenuation hinder their practical application. The limited operating voltage also makes it difficult to satisfy the increasing demand of high energy density in future applications. Inspired by the high voltage platform of Ni-rich LiNi(0.8)Co(0.1)Mn(0.1)O(2), we design and prepare a Li(1.2)Ni(0.32)Co(0.04)Mn(0.44)O(2) (LLMO811) cathode material with increased Ni content via the acrylic acid polymerization method and regulate the amounts of excess lithium of LLMO. It is found that LLMO-L3 with 3% excess lithium has the highest initial discharge capacity of 250 mA h g(-1) with a coulombic efficiency of 83.8%. Taking advantage of a high operating voltage of about 3.75 V, the material achieves an impressive high energy density of 947 W h kg(-1). Moreover, the capacity at 1C reaches 193.2 mA h g(-1), which is higher than that of ordinary LLMO811. This large capacity is attributed to the highly reversible O redox reaction, and the strategy used to achieve this would throw some light on the exploration of high-energy-density cathodes.
作者机构：
[Gao, Enduo; Li, Hongjian] Cent South Univ, Sch Phys & Elect, Changsha 410083, Peoples R China.;[Chen, Xiaoshaung; Jin, Rong; Fu, Zhenchu; Chen, Jian; Li, Guanhai] Chinese Acad Sci, Shanghai Inst Tech Phys, State Key Lab Infrared Phys, Shanghai 200083, Peoples R China.;[Cao, Guangtao] Changsha Univ Sci & Technol, Sch Phys & Elect Sci, Changsha 410004, Peoples R China.;[Deng, Yan] Hunan First Normal Univ, Sch Phys & Chem, Changsha 410205, Peoples R China.;[Li, Guanhai] Univ Chinese Acad Sci, Hangzhou Inst Adv Study, Hangzhou 310024, Peoples R China.
通讯机构：
[Guanhai Li] S;State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China<&wdkj&>Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China
摘要：
Dynamical control of perfect absorption plays an indispensable role in optical switch and modulators. However, it always suffers from the limited modulation range, small depth, and susceptible absorption efficiencies. Here, we propose a new strategy based on Friedrich–Wintgen bound states in the continuum (F–W BICs) to realize a tunable perfect absorber with large dynamic modulation range. For proof of concept, we demonstrate a pentaband ultrahigh absorption system consisting of graphene gratings and graphene sheets through elaborately tuning F–W BIC. The nature of the F–W BIC arises from the destructive interference between Fabry–Perot resonance and guided mode resonance modes in the coherent phase-matching condition. The radiation channels are avoided from crossing. The BIC can be dynamically modulated by engineering the Fermi level of graphene gratings, which breaks the traditional modulation methods with an incidence angle. Remarkably, the perfect absorber with this F–W BIC approach achieves the largest modulation range of up to 3.5 THz. We believe that this work provides a new way to dynamically engineer perfect absorption and stimulates the development of multiband ultracompact devices.
通讯机构：
[Wu, D ] C;[Liu, JH ] H;Hunan Inst Technol, Dept Math & Phys, Hengyang 421002, Peoples R China.;Changsha Univ Sci & Technol, Sch Phys & Elect Sci, Changsha 410114, Peoples R China.
摘要：
By using density functional theory calculations combined with the nonequilibrium Green's function method and machine learning, we systematically studied the thermoelectric properties of four kinds of porous graphene nanosheets (PGNS) before and after nitrogen doping. The results show that the thermoelectric performance of porous graphene nanosheets along the armchair or zigzag chiral direction is improved due to the dramatically enhanced power factor caused by nitrogen doping. The calculated ZT values of nitrogen-doped porous graphene nanosheets are boosted by about one order of magnitude compared with those of undoped porous graphene nanosheets at room temperature. More importantly, an anisotropic thermoelectric transport is found in the nitrogen-doped porous graphene nanosheets. The results show that the ZT values of nitrogen-doped porous graphene nanosheets along the zigzag transport direction are nearly 11 times larger than those of them along the armchair transport direction. These results reveal that the thermoelectric properties of porous graphene nanosheets can be well regulated by nitrogen doping, and provide a good theoretical guidance for their application in thermoelectric devices.
通讯机构：
[Lijun Tang] S;School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114, China<&wdkj&>Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering, Changsha 410114, China<&wdkj&>Key Laboratory of Electromagnetic Environment Monitoring and Modeling in Hunan Province, Changsha 410114, China<&wdkj&>Author to whom correspondence should be addressed.
关键词：
quartz flexible accelerometer;electric field coupling noise;lock-in amplifier circuit
摘要：
The internal electric field coupling noise of a quartz flexible accelerometer (QFA) restricts the improvement of the measurement accuracy of the accelerometer. In this paper, the internal electric field coupling mechanism of a QFA is studied, an electric field coupling detection noise model of the accelerometer is established, the distributed capacitance among the components of the QFA is simulated, the structure of the detection noise transfer system of different carrier modulation differential capacitance detection circuits is analyzed, and the influence of each transfer chain on the detection noise is discussed. The simulation results of electric field coupling detection noise show that the average value of detection noise can reach 41.7 mu g, which is close to the effective resolution of the QFA, 50 mu g. This confirms that electric field coupling detection noise is a non-negligible factor affecting the measurement accuracy of the accelerometer. A method of adding a high-pass filter to the front of the phase-shifting circuit is presented to suppress the noise of electric field coupling detection. This method attenuates the average value of the detected noise by about 78 dB, and reduces the average value of the detected noise to less than 0.1 mu g, which provides a new approach and direction for effectively breaking through the performance of the QFA.
通讯机构：
[Xiang, D ] N;[Fan, ZQ ] C;Nankai Univ, Inst Modern Opt, Ctr Single Mol Sci, Key Lab Microscale Opt Informat Sci & Technol, Tianjin 300350, Peoples R China.;Changsha Univ Sci & Technol, Sch Phys & Elect Sci, Changsha 410114, Peoples R China.;Nankai Univ, Smart Sensing Interdisciplinary Sci Ctr, Sch Mat Sci & Engn, Tianjin 300350, Peoples R China.
摘要：
The molecular binding orientation with respect to the electrode plays a pivotal role in determining the performance of molecular devices. However, accomplishing in situ modulation of single-molecule binding orientation remains a great challenge due to the lack of suitable testing systems and characterization approaches. To this end, by employing a developed STM-BJ technique, we demonstrate that the conductance of pyridine-anchored molecular junctions decreases as the applied voltage increases, which is determined by the repeated formation of thousands of gold-molecule-gold dynamic break junctions. In contrast, the static fixed molecular junctions (the distance between two electrodes is fixed) with identical molecules exhibit a reverse tendency as the bias voltage increases. Supported by flicker noise measurements and theoretical calculations, we provide compelling evidence that the orientation of nitrogen-gold bonds (a universal coordinate bond) in the pyridine-anchored molecular junctions can be manipulated to align with the electric field by the synergistic action of the mechanical stretching force and the electric fields, whereas either stimulus alone cannot achieve the same effect. Our study provides a framework for characterizing and regulating the orientation of a single coordinate bond, offering an approach to control electron transport through single molecular junctions.
关键词：
impurity magnetization;localized magnetic states;parity anomaly;quantum anomalous Hall systems
摘要：
We investigate the local magnetic states of impurities in quantum anomalous Hall (QAH) systems and observe that with an increasing band gap, the magnetic region of impurities expands in the QAH phase, while it contracts in the ordinary insulator (OI) phase. During the transition between the QAH and the OI phase, the magnetization area undergoes a significant transformation from a broad region to a narrow strip, which serves as a distinctive characteristic of the parity anomaly in the localized magnetic states. Furthermore, the presence of the parity anomaly leads to notable alterations in the dependence of the magnetic moment and magnetic susceptibility on the Fermi energy. Additionally, we analyze the spectral function of the magnetic impurity as a function of Fermi energy for both the QAH and OI phases.
摘要：
Exceptional points (EPs) in non-Hermitian systems embody abundant new physics and trigger various novel applications. In the optical force system, the motion of a particle near its equilibrium position is determined by the optical force stiffness matrix (OFSM), which is inherently non-Hermitian when the particle is illuminated by vortex beams. In this study, by exploiting the rapid variations in eigenvalues and the characteristics of particle motion near EPs of the OFSM, we propose a method to sort particles with subtle differences in their radii or refractive indices based on their trajectories in air. We demonstrate that the trajectory of a particle with parameters slightly larger than those corresponding to certain EPs closely resembles an ellipse. The increase in the major axis of the ellipse can be several orders of magnitude larger than the increase in particle radius. Furthermore, even a slight change in the refractive index can not only significantly alter the size of the ellipse but also rotate its orientation angle. Hence, particles with subtle differences can be distinguished by observing the significant disparities in their trajectories. This approach holds promise as a technique for the precise separation of micro and nanoscale particles.
摘要：
为了研究当单层石墨烯位于多层Fabry-Pérot(F-P)谐振腔中时, 系统近全吸波模式与多层F-P谐振腔数目之间的关系, 同时提高系统对吸波模式的调控能力, 采用严格耦合波分析法, 对石墨烯多层F-P谐振腔系统的吸波响应进行了研究, 分析了临界耦合条件下双层和3层F-P谐振腔结构的光谱响应特征。结果表明, 双层和3层F-P谐振腔可调谐近全吸波体, 分别形成了两个99%以上和3个96%以上的近全吸波模式; 通过对石墨烯掺杂可以实现对3层F-P谐振腔系统吸波特性的调节, 通过改变3层谐振腔的结构可以控制系统吸收模式的数量和相对位置。该研究为可调近全吸波系统引入更丰富的吸波线型。 To find the connection between the number of near-full absorbing mode and the Fabry-Pérot (F-P) multilayer F-P cavity when single-layer graphene is located in the multilayer F-P cavity and to improve the system’s controlling ability to the diversity of absorbing modes, rigorous coupled-wave analysis was adopted. The response characteristics of two-layer and three-layer F-P resonator under critical coupling conditions were analyzed. The results show that perfect absorbing modes of more than 99% and 96% can be respectively formed in two-layer and three-layer F-P cavity systems. Among them, the absorption characteristics of three-layer F-P nested cavity system can be adjusted by doping graphene, and the number and relative positions of absorption modes of three-layer nested cavity can be controlled by changing the structure of three-layer F-P cavity. The system introduces a richer absorbing line type.
关键词：
ECH wave;frequency-chirping fine structure;spatial distribution
摘要：
Electron cyclotron harmonic (ECH) waves can scatter electrons into the atmosphere causing diffuse aurora with diffusion coefficients depending on the wave frequency. Here we report the Van Allen Probe observations of chirping ECH elements, which are fine structures with a frequency-chirping rate of ∼kHz/s. 1,834 samples are identified in the 51-month database and over 93 percent of them exhibit a falling tone pattern. ECH elements cover a broad region from 18 Magnetic Local Time (MLT) through dawn to 14 MLT with L = 4 − 7, and mainly occur in the region of 00–07 MLT with L = 5 − 6. More ECH elements are observed with the occurrence region extending to lower L-shells during the geomagnetic activity period. Chirping ECH elements can propagate to |MLAT| ∼ 20°, but be confined by the contour of magnetic field strength. The statistical results can be applied on the global simulation of ECH-induced electron penetration.
All chirping electron cyclotron harmonic (ECH) elements (1,834 samples) occur in the first harmonic band, showing a distinct preference to falling tone structures (>93%)
The chirping ECH elements cover a broad region of radiation belts, with a higher occurrence in the region of 00–07 Magnetic Local Time (MLT) with L = 5 − 6
As the AE index increases, the occurrence region of chirping ECH elements extends to lower L-shells
Electron cyclotron harmonic (ECH) wave plays a critical role in the magnetospheric dynamics by diffusing energetic electrons into the atmosphere. Previous studies show that the diffusion coefficients are very sensitive to the wave frequency. Here based on the Van Allen Probes data, we report the presence of ECH frequency chirping structures (so-called chirping ECH elements) in the magnetosphere. The duration of ECH elements is comparable with the well-known chorus elements. Adopting a 51-month database, we study the statistical properties of such ECH elements. All of the ECH elements occur in the first harmonic band and more than 93 percent of them are falling tones. ECH elements cover a broad range of L = 4 − 7 from 18 MLT through dawn to 14 MLT, and mainly appear in the region L = 5 − 6 at the midnight to dawn sector. It is widely accepted that ECH waves generally occur in the equatorial region. Here the ECH elements can propagate to |MLAT| ∼ 20°. Moreover, when the geomagnetic activities get more intense, more ECH elements can be observed and they can extend to lower L-shells. The current results could be important for investigating their generation mechanism and quantifying the ECH-electron resonance process.
通讯机构：
[Junlong Tang] S;School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114, China<&wdkj&>Author to whom correspondence should be addressed.
摘要：
Surface defects, which often occur during the production of aluminum profiles, can directly affect the quality of aluminum profiles, and should be monitored in real time. This paper proposes an effective, lightweight detection method for aluminum profiles to realize real-time surface defect detection with ensured detection accuracy. Based on the YOLOv5s framework, a lightweight network model is designed by adding the attention mechanism and depth-separable convolution for the detection of aluminum. The lightweight network model improves the limitations of the YOLOv5s framework regarding to its detection accuracy and detection speed. The backbone network GCANet is built based on the Ghost module, in which the Attention mechanism module is embedded in the AC3Ghost module. A compression of the backbone network is achieved, and more channel information is focused on. The model size is further reduced by compressing the Neck network using a deep separable convolution. The experimental results show that, compared to YOLOv5s, the proposed method improves the mAP by 1.76%, reduces the model size by 52.08%, and increases the detection speed by a factor of two. Furthermore, the detection speed can reach 17.4 FPS on Nvidia Jeston Nano’s edge test, which achieves real-time detection. It also provides the possibility of embedding devices for real-time industrial inspection.
关键词：
Breakdown voltage;LDMOS;Multi -dimensional accumulation gate;Specific on -resistance
摘要：
A novel multi-dimensional accumulation gate (MDAG) lateral double-diffused MOS (LDMOS) with ultra-low specific on-resistance (Ron,sp) is proposed and investigated by simulation. The MDAG LDMOS is composed of the MDAG, the trench source, and the N-Buffer. In the on-state, the bulk electron channels are formed in the P -well and the multi-dimensional electron layers are formed in the drift region. Meanwhile, the trench source shortens the current path length. Thus, the Ron,sp is greatly reduced. In the off-state, the N-Buffer is used to form a PN junction with the P-Substrate to obtain the ideal reverse characteristics of the accumulation model LDMOS, and thus the high breakdown voltage (BV) is achieved. The simulation results show that the proposed MDAG LDMOS has a Ron,sp of 0.33 m & omega; cm2 and a BV of 181.4 V. The figure of merit (FOM) is as high as 99.7 MW/cm2. Hence, the tradeoff between Ron,sp and BV is greatly improved, and the silicon limit of RESURF is broken.
关键词：
nonlinear Hall effect;third harmonic generation;Dirac system
摘要：
We theoretically investigate the third-order nonlinear Hall effect by employing the quantum kinetic equation and present an analytic formula for the third-order harmonic conductivity, where the intraband and the mixed inter-band contributions caused by the external electric field as well as the multiphoton process dressed Berry curvature are unveiled. These results are applied in a two-dimensional (2D) Dirac system. We find that the third-order harmonic conductivity exhibits a crossover from the negative to positive value due to the intraband transition of the electrons in the low-frequency region, whereas a kink or dip structure due to the multiphoton process between the conduction and valence bands in the high-frequency region. In experiment, these features can be identified by detecting the transverse current. Our work deepens the understanding of the multiphoton process in the nonlinear transport of topological materials and enlightens a possible way to its characterization in experiments.
作者机构：
[Kuang, Hui-Ling; Wu, Cheng-Wei; Zhou, Wu-Xing; Zhou, WX; Liu, Long-Ting; Li, Shi-Yi; Zeng, Yu-Jia; Xie, Guofeng] Hunan Univ Sci & Technol, Sch Mat Sci & Engn, Hunan Prov Key Lab Adv Mat New Energy Storage & Co, Xiangtan 411201, Peoples R China.;[Wu, Dan] Changsha Univ Sci & Technol, Sch Phys & Elect Sci, Hunan Prov Key Lab Flexible Elect Mat Genome Engn, Changsha 410114, Peoples R China.
通讯机构：
[Wu, D ] C;[Zhou, WX ] H;Hunan Univ Sci & Technol, Sch Mat Sci & Engn, Hunan Prov Key Lab Adv Mat New Energy Storage & Co, Xiangtan 411201, Peoples R China.;Changsha Univ Sci & Technol, Sch Phys & Elect Sci, Hunan Prov Key Lab Flexible Elect Mat Genome Engn, Changsha 410114, Peoples R China.
摘要：
In this study, we employ a machine-learning potential approach based on first-principles calculations combined with the Boltzmann transport theory to investigate the impact of lithium-ion de-embedding on the thermal conductivity of LiFePO4, with the aim of enhancing heat dissipation in lithium-ion batteries. The findings reveal a significant decrease in thermal conductivity with increasing lithium-ion concentration due to the decrease in phonon lifetime. Moreover, removal of lithium ions from different sites at a given lithium-ion concentration leads to distinct thermal conductivities, attributed to varying anharmonicity arising from differences in bond lengths and bond strengths of the Fe-O bonds. Our work contributes to a fundamental understanding of the thermal transport properties of lithium iron phosphate batteries, emphasizing the pivotal role of lithium-ion detachment and intercalation in the thermal management of electrochemical energy storage devices.
