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A Review on Band Unfolding Technique and Its Applications CHEN Jia-xin, CHEN Ming-xing Progress in Physics    2023, 43 (2): 25-40.   DOI: 10.13725/j.cnki.pip.2023.02.001 Abstract （2025）      PDF （58451KB）（2000）       First-principles methods based on the density-functional theory have been widely applied to investigate structures and properties of materials and further to design new functional materials. The supercell method is usually used for the modeling of doped systems and interfaces. Unfortunately, the use of supercells leads to band foldings. As a result, the nature of electronic bands may be hidden, which brings difficulties in understanding the effects of doping and interfacing on the band structure of materials. This review provides recent advances in band unfolding technique within the plane-wave method and the linear combination of atomic orbitals. It also gives unfolding of phononic bands and lists a number of codes for band unfolding calculations. Finally, it presents a few applications of the technique and an outlook on further research options. Related Articles | Metrics

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Historic Origin of Quantum Entanglement in Particle Physics SHI Yu Progress in Physics    2023, 43 (3): 57-67.   DOI: 10.13725/j.cnki.pip.2023.03.001 Abstract （1540）      PDF （1284KB）（1452）       The historic origin of quantum entanglement in particle physics is studied systematically and in depth. In 1957, Bohm and Aharonov noted that the 1950 Wu-Shaknov experiment had realized the discrete version of the Einstein-Podolsky-Rosen correlation. Indeed this experiment was definitely the first experimental realization of spatially separated quantum entanglement in history. Such an experiment had been proposed by Wheeler, as a test of quantum electrodynamics, but his calculation was erroneous. The correct theoretical calculations were made by Ward and Pryce and also by Snyder, Pasternack and Hornbostel. The entangled state of the photons also satisfies the selection rule of C. N. Yang in 1949. After the publication of Bell inequality in 1964, discussions on whether Wu-Shaknov experiment can be exploited in testing the inequality inspired the progress of this field, and a new experiment was done by Wu’s group. In 1957, Lee, Oehme and Yang established the quantum mechanical formulation of the kaons, and discovered that neutral kaon is a two-state system. The following year，Goldhaber, Lee and Yang wrote down entangled states of a pair of kaons for the first time, in which each kaon is allowed to be charged or neutral, as the entanglement in internal degrees of high energy particles beyond photons written down for the first time. In 1960, as an unpublished work, Lee and Yang discussed an entangled state of a pair of neutral kaons. Such entangled kaons widely exist in meson factories later on. Several physicist are also introduced, especially Ward. Related Articles | Metrics

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Gauge Field and Fiber Bundle：Its Contents, Methods, and Meanings  ZHAO Song-nian , LU Bo, CHEN Ken, HUANG Xu Progress in Physics    2023, 43 (1): 10-24.   DOI: 10.13725/j.cnki.pip.2023.01.002 Abstract （1507）      PDF （708KB）（2328）       Related Articles | Metrics

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Types and Properties of Copper-Oxide Superconductors with Critical Temperatures Above 110 K TONG Shu-yun, CAI Chuan-bing Progress in Physics    2023, 43 (3): 68-83.   DOI: 10.13725/j.cnki.pip.2023.03.002 Abstract （1366）      PDF （4571KB）（1117）       Oxide superconductor is one of the most important forms of unconventional superconductors, in which the transition temperatures of thallium series, mercury series and copper-carbon series superconductors can reach 110 K or above. High superconducting transition temperature and irreversible magnetic field in liquid nitrogen temperature region have attracted much attention. Obviously, the high superconducting critical temperature increases the choice of cooling medium for superconducting applications. Economical and practical coolants are expected to expand the application fields of these high superconducting transition temperature (Tc ) superconductors and increase the feasibility of long-term operation. In this paper, the development and superconducting properties of 110 K superconducting materials including thallium, mercury and copper-carbon superconductors are introduced and summarized, and the factors affecting the superconducting transition temperature are analyzed theoretically to qualitatively explain the reasons for the high Tc  of high temperature superconductors. Special attention is paid to the analysis of the differences of their irreversible fields, and the possible new applications of these high critical temperature superconductors are prospected. Related Articles | Metrics

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Vortex state in a nematic triplet superconductor YANG Miao-miao, XIANG Ke, WANG Da, WANG Qiang-hua Progress in Physics    2023, 43 (5): 131-141.   DOI: 10.13725/j.cnki.pip.2023.05.001 Abstract （1132）      PDF （452KB）（432）       The discovery of nematic triplet superconductivity in doped topological insulators CuxBi2Se3 triggers interest in the identification of the d-vector of the triplet, which is related to the antinodal direction of the gap function and determines whether the superconductor is topological. We perform self-consistent analysis of the vortex state properties in a nematic spin-triplet px-wave superconductor. We first derive a Ginzburg-Landau theory to determine the shape of the vortex and vortex lattice. We find the spatial profile of the isolated vortex is elongated along the antinodal direction, and the vortex lattice is a distorted triangular lattice elongated along x, becoming square in the specific case of a small circular Fermi surface. Finally, we calculate the local density of states self-consistently for an isolated vortex and the vortex lattice using the microscopic Bogoliubov-de Gennes equation. We find that the profile of the local density of states at low in-gap energies is always elongated along the antinodal direction. Our findings are valuable for the experimental detection of the antinodal direction of the gap function in nematic triplet superconductors, and subsequently the identification of the topological character of the superconducting state as in CuxBi2Se3. Related Articles | Metrics

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Perovskite Solar Cells Stability Factors And Encapsulaiton For Performance Enhancement DAI Jiaqi, ZHANG Dong, WU Xiaoshan Progress in Physics    2024, 44 (1): 19-48.   DOI: 10.13725/j.cnki.pip.2024.01.003 Abstract （1020）      PDF （5083KB）（768）       Perovskite solar cells, which are considered the third generation of new concept solar cells, are known for their high photoelectric conversion efficiency, low cost, and flexible processing advantages, and have been rapidly development in recent years. its photoelectric conversion efficiency is gradually comparable to that of silicon cells and has been close to the level required for industrial applications. However, the main problem with the industrial application of perovskite solar cells is their stability. Researchers need to solve the biggest problem of how to maintain high efficiency for a long time in perovskite solar cells. Encapsulation is currently being widely studied as a solution to the external stability issue of perovskite solar cells. A good encapsulation can not only solve the stability problem of the device but also ensure the safety of the device and extend the service life. The stability of perovskite solar cells and the conditions for testing it are briefly described in this paper. In the end, the various encapsulation structures, techniques, and materials for perovskite solar cells are explained. The continuous advancement of encapsulation research will lead researchers to optimize and solve existing problems, leading to the eventual industrialization of perovskite solar cells on a large scale.  Related Articles | Metrics

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High-Performance Physiological Signal Sensors Based on Stretchable Organic Electrochemical Transistors ZHANG Chen-hong , CHEN Yan-ping , WANG Gang ∗ , ZHANG Qing-hong , LI Yao-gang , WANG Hong-zhi Progress in Physics    2023, 43 (1): 1-9.   DOI: 10.13725/j.cnki.pip.2023.01.001 Abstract （961）      PDF （1055KB）（885）       Recently, organic electrochemical crystals (OECT) using conjugated polymers as channel materials have become a hot research topic due to their ease of preparation, ionelectron conversion capability and biointerface compatibility. However, most of the reported OECT channel materials for OECT are p-type conjugated polymers (hole transport), while few OECTs have been developed based on n-type conjugated polymers (electron transport), and the unbalanced development hinders the realization of complex complementary circuits. The recently reported n-type Poly (benzimidazobenzophenanthroline) (BBL) OECT of polyconjugated polymers provides an effective solution to the above problem. However, BBL films are inherently brittle and cannot be stretched to meet the use of flexible devices, which greatly hinders their application and development. In this work, we propose the preparation of a device stretchable n-type BBL OECT device and verify its feasibility for sweat sensing. Related Articles | Metrics

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Second-Order Nonlinear Optics in Transition Metal Dichalcogenides WU Hui , QIN Chun-bo , ZHANG Chun-feng Progress in Physics    2023, 43 (3): 84-95.   DOI: 10.13725/j.cnki.pip.2023.03.003 Abstract （866）      PDF （5051KB）（1222）       Second-order nonlinear optics is a crucial technique for light frequency conversion with broad applications in scientific research and technological advancements. Monolayer transition metal dichalcogenides exhibit extraordinarily high second-order nonlinear susceptibilities, indicating their significant potential for efficient nonlinear optical response. Maintain the giant nonlinear coefficient of monolayer, expand material thickness and frequency response region, and improve nonlinear response is an important challenge. This paper presents an overview of the regulation of second-order nonlinear optical effects based on monolayer transition metal dichalcogenides. We discuss the frequency dependence of monolayer transition metal dichalcogenides, as well as multi-layer stacking of different symmetric phases. Additionally, we summarize the potential applications of their nonlinear optical effects.  Related Articles | Metrics

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Self-trapped Excitons in Metal Halide Perovskites  ZHANG Qin-kai , WANG Yu-xiao , ZHANG Chun-feng Progress in Physics    2023, 43 (6): 161-177.   DOI: 10.13725/j.cnki.pip.2023.06.001 Abstract （776）      PDF （9908KB）（1002）       In polar crystals, excited electron-hole pairs can be captured by the deformation potential field created by lattice distortion upon photoexcitation, due to strong electron-phonon interactions, thereby forming self-trapped excitons. Metal halide perovskites are semiconductors that display efficient self-trapped exciton luminescence in various systems due to their ionic crystal nature with strong electron-phonon interactions and a deformable lattice. Consequently, they are considered ideal for creating high-quality white light sources. However, the understanding of the self-trapped exciton luminescence mechanism in metal halide perovskites is still relatively scarce and lags far behind the development of devices. To this end, this paper summarizes the recent research progress on the formation conditions, formation mechanism and related excited state dynamics of self-trapped excitons in metal halide perovskites semiconductors from the perspective of the fundamental physics of self-trapped excitons, and gives an outlook on the future research based on the self-trapped exciton mechanism in this system, so as to provide a clearer physical image for the study of self-trapped excitons in this system Related Articles | Metrics

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Environmental Stability of 2D Transition Metal Dichalcogenides ZHOU Zhen-jia , XU Jie , GAO Li-bo Progress in Physics    2023, 43 (4): 97-116.   DOI: 10.13725/j.cnki.pip.2023.04.001 Abstract （736）      PDF （837KB）（934）       Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with a unique unity of favorable electronic and mechanical properties have been developed for fundamental studies and applications in electronics, spintronics, optoelectronics, energy harvesting and catalysis. However, as they are unstable under harsh conditions, and prone to degradation in the ambient environment, most TMDCs applications are limited. In this review, we analyze the recent advances in the research of environmental stability in TMDCs, covering the latest growth methods, the fundamental mechanisms for stability and kinds of routes to protect 2D TMDCs materials from aging and deterioration. By analyzing key factors that affect TMDCs stability from the growth process, we present a short review of optimizing growth methods for improving the stability of TMDCs. Finally, by providing insights into existing factors, this review is expected to guide the growth of stable TMDCs, which could lead to a new potential approach to growing advanced materials and designing more unexplored heterostructures.  Related Articles | Metrics

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Low-Frequency Raman Detection of Antiferromagnetic Spin Waves in Cr 2O 3 Dong Biao , CUI Jun , TIAN Yuan-zhe , WU Di , ZHANG Qi Progress in Physics    2023, 43 (5): 142-150.   DOI: 10.13725/j.cnki.pip.2023.05.002 Abstract （642）      PDF （4272KB）（547）       The antiferromagnetic (AFM) spin waves are promising for being utilized in highspeed and energy-efficient information processing. However, the excitation and detection of terahertz spin waves in AFM systems is challenging. Here, we demonstrate low-frequency Raman spectroscopy as a powerful tool for spin-wave detection in AFM systems. We present a systematic study of AFM magnons in Cr2O3, a prototypical uniaxial antiferromagnet, via Raman measurements down to 2.3 cm−1 (69 GHz). We resolved the magnon Zeeman splitting and the spin-flop transition. We further determined the sign of angular momentum of the magnon branches via polarization-resolved Raman processes. We also obtained the anisotropy energy, the g-factor, and the spin-flop field of Cr2O3 as a function of temperatures and magnetic fields. A spin-wave renormalization theory accounts for all experimental observations.  Related Articles | Metrics

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Research Progress on Single-Mode Regulation Methods for Whispering Gallery Mode Microcavities LIU Shuo, WANG Yu-chen, WANG Xiu-hua, HOU Rui Progress in Physics    2023, 43 (4): 117-130.   DOI: 10.13725/j.cnki.pip.2023.04.002 Abstract （618）      PDF （483KB）（1398）       Whispering gallery mode (WGM) microcavities have attracted wide attention due to their small mode volume, ultra-high Q value, and low threshold. However, in rotationally symmetric WGM microcavities, multiple longitudinal mode laser radiation can be generated, and the directionality of the radiation is poor, which limits its practical applications. Finding effective methods to achieve single-mode radiation of WGM lasers is a key issue for microcavity lasers to move toward practical applications. This review focuses on several methods of single-mode modulation of WGM lasing in recent years, including reducing cavity size, adding mode selection structure, based on the vernier effect, parity-time symmetry breaking, deformed microcavity, etc. This review aims to provide a reference for researchers in related fields and deepen their understanding of the physical mechanism of single-mode modulation of WGM lasing. Related Articles | Metrics

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Cell Tissue Simulations Based on Active Network Models LI Zhu-qin, LEI Qun-li, MA Yu-qiang Progress in Physics    2023, 43 (2): 41-55.   DOI: 10.13725/j.cnki.pip.2023.02.002 Abstract （613）      PDF （9233KB）（1008）       In the last decade, motivated by advances in cell biology, theoretical studies of the cell tissue as active matter have emerged as a new area in soft matter physics. This article reviews recent theoretical progresses based on the active network (AN) model of cell tissue. In the mesoscopic scale, the non-equilibrium dynamics of cell tissue is mainly driven by the self-propulsion of cells and non-propulsion activities, like active contractility or cellular tension/volume oscillation. AN models of self-propelled cells can reproduce complex dynamics of cell tissue in vivio, such as activity/adhesion driven solid-liquid transition, flocking and active turbulence. The AN model incorporating cellular tension fluctuation can also simulate the cell volume oscillation waves in embryo of Drosophila, and predict the fluctuation-driven solid-liquid transition of cell tissue. The structural phase transition and density fluctuation of cell tissue were also studied by using AN models, which deepens our understanding of this unique non-equilibrium soft matter system. Related Articles | Metrics

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Attractor Dynamics in Spatial Cognition WANG Zi-qun , WANG Tao , LIU Feng Progress in Physics    2023, 43 (6): 188-201.   DOI: 10.13725/j.cnki.pip.2023.06.003 Abstract （560）      PDF （3411KB）（757）       The mammalian navigation system comprises various kinds of neurons responsible for position perception and spatial path planning, involving the integration of multiple information sources. As a unified brain theory capable of providing explanations for complex cognitive functions like memory and decision-making, the theory of attractor dynamics can elucidate the firing dynamics of neurons and path integration in the navigation system. This review describes recent advances in attractor dynamics in spatial cognition. First, it provides a brief overview of computational neuroscience and the general theory of attractor dynamics. Subsequently, focusing on the continuous attractor dynamics, it delves into the dynamical characteristics and functional significance of head direction cells and grid cells. Finally, an extension and prospects of the attractor theory for spatial cognition are presented. Related Articles | Metrics

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Progress in First-Principles Methods for Simulation of Warm Dense Matter ZHANG Hang, CHEN Mo-han Progress in Physics    2024, 44 (2): 49-72.   DOI: 10.13725/j.cnki.pip.2024.02.001 Abstract （530）      PDF （2466KB）（473）       Warm Dense Matter (WDM) represents a transitional state of matter situated between condensed matter and plasma, emerging as a cutting-edge research direction within the realms of planetary physics, laboratory astrophysics, and inertial confinement fusion in the field of high-energy density physics. WDM is characterized by significant quantum effects, partial ionization, strong coupling, electron degeneracy, and thermal effects, necessitating a description based on fundamental quantum mechanical theories. In recent years, simulations and calculations based on quantum mechanics’ first principles have rapidly advanced, increasingly becoming an effective tool for a deeper understanding of WDM properties. On one hand, applying First Principles widely used in condensed matter physics and materials science to WDM poses considerable challenges, especially under extreme conditions such as broad temperature ranges and high pressures, which require continuous improvements to existing first-principle algorithms and software. On the other hand, the rapid development of machine learning-based molecular dynamics methods offers new tools for simulating WDM. In this review, we initially revisit traditional first principles applicable to WDM simulations, including Kohn-Sham Density Functional Theory and Orbital-free Density Functional Theory. Subsequently, we introduce newly developed methods and software, such as Extended First Principles Molecular Dynamics and Stochastic Density Functional Theory, the latter of which has been implemented in the domestically developed open-source density functional theory software, Atomic-orbital Based Ab-initio Computation at UStc (ABACUS). These innovative approaches significantly boost the computational scale and efficiency of WDM studies, thereby elevating the precision of structural, dynamical, and transport coefficient calculations related to WDM Related Articles | Metrics

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Recent Progress on the Effect of the Electronic Structure on Electrocatalytic Performance of Single Atom Catalysts HE Yue-xuan, WANG Tong-hui, WEN Zi, JIANG Qing Progress in Physics    2024, 44 (3): 136-156.   DOI: 10.13725/j.cnki.pip.2024.03.004 Abstract （484）      PDF （2081KB）（231）       Single atom catalysts (SACs) are promising candidates for various catalytic systems due to their unique electronic structures and the highest atom utilization. Modulating the electronic structure of SACs catalysts is the key to its further development, can optimize the adsorption and bonding energies of the catalysts by regulating the electronic properties, and thus improves the catalytic activity and stability. Herein, we provide a comprehensive understanding of SACs in catalysis through their electronic structures and their associated knowledges. Various electronic properties have been discussed, such as energy band structure, orbital hybridization and associated spin states, etc. Electrocatalysis as a technology for reducing carbon emissions and utilizing renewable energy sources which can address growing pollution problems, is receiving increasing attention, making the design of high-performance catalysts critical. From this review, we discusse how the electronic structure of SACs affects their electrochemical catalytic performance and explore its relationship with activity and stability of SACs. The understanding of the fundamentals of electronic structures in catalytic processes can provide rational guidance for the design of catalysts in various catalytic reactions in the future Related Articles | Metrics

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Research Progress on the Regulation of Metal-Site Bismuth Doping in Halide Perovskites HUANG Xiao-rui, SUN Yue, HE Sheng-rong, XING Jun Progress in Physics    2024, 44 (2): 73-95.   DOI: 10.13725/j.cnki.pip.2024.02.002 Abstract （473）      PDF （8816KB）（633）       Related Articles | Metrics

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Phase Transition in Black Phosphorus Induced by Thermal Driven Diffusion of Metal CAO Tianjun , SHAN Junjie , WANG Gang, LIN Junhao, LIANG Shijun, MIAO Feng Progress in Physics    2024, 44 (1): 1-8.   DOI: 10.13725/j.cnki.pip.2024.01.001 Abstract （469）      PDF （6736KB）（476）       Two-dimensional (2D) materials are atomically flat and can be stacked into van der Waals heterostructures, as well as contain abundant physical phenomena and excellent electrical properties. The study of phase transition behavior of 2D materials has been the frontier of condensed matter physics and materials science. In our study, the stage-controlled phase transition induced by thermal-driven metal diffusion in black phosphorus (BP) is realized for the first time. Through thermal annealing treatment of the BP-In interface, the phase transition phenomenon from BP pure phase to BP/InP mixed phase and then to InP pure phase is observed. Combined with the characterization techniques of transmission electron microscopy and Raman spectroscopy, the mechanism responsible for phase transition is deeply analyzed, revealing that the thermal-driven metal diffusion behavior in BP-In is the main inducement of phase transition. The two key threshold temperatures (initiation of phase transition and transformation of pure phase) during the stepwise phase transition are obtained by manipulating the two degrees of freedom (temperature and time) which affect the energy supply in the thermal driving, where are 300 and 350 °C , respectively. This study provides more possibilities for expanding the applications of BP-based electronic and optoelectronic devices.  Related Articles | Metrics

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Theoretical Insights into the Triplet-Pair State of Singlet Fissio TONG Lei, ZHANG Chun-feng Progress in Physics    2024, 44 (3): 112-122.   DOI: 10.13725/j.cnki.pip.2024.03.002 Abstract （416）      PDF （1708KB）（414）       Singlet fission is a photophysical process in organic materials where a photoexcited singlet exciton splits into two triplet excitons. This process has gained a lot of interest in the past decade for enhancing the efficiency of photovoltaic conversion. Precious work identified a crucial intermediate state in singlet fission, and the construction of the wave function for this correlated triplet-pair state poses a significant challenge. This article serves as a comprehensive introduction to theoretical models designed for constructing the wave function of the correlated triplet-pair. Subsequently, we delve into an exploration of the intricate effects of vibrational, orbital, and spin interactions on the formation and dissociation of the intermediate state. Finally, we conclude with a succinct summary of the challenges anticipated to shape the landscape of future theoretical research in this field. Related Articles | Metrics

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Wave Velocity Measurement and Modulation of Surface Acoustic Waves in Piezoelectric Materials  WANG Ren-fei, LIU Xiao, WU Meng-meng, LIN Xi, LIU Yang Progress in Physics    2024, 44 (3): 103-111.   DOI: 10.13725/j.cnki.pip.2024.03.001 Abstract （387）      PDF （4278KB）（599）       In addition to the well-known conventional acoustic wave propagation mode in three-dimensional solids, there exists the surface acoustic wave propagation mode where energy is only concentrated near the two-dimensional interface. In this work, utilizing the piezoelectric and inverse piezoelectric effects from GaAs substrates, we achieve the conversion between radiofrequency electromagnetic waves and surface acoustic waves with planar interdigital transducers, and successfully measure the surface acoustic wave velocity on a sample with a dimension of only 4 mm using superheterodyne-scheme lock-in technique, yielding a result of (2.9±0.1) km/s. We also fabricate a uniaxial stress cell with piezoelectric ceramics, capable of applying uniaxial strains up to approximately 10−4 to the sample, and observe the influence of strain on the surface acoustic wave velocity. We measure the surface acoustic wave velocity of the important semiconductor GaAs under stress, demonstrating the capability of this velocity measurement technique to probe the internal mechanical properties of solids in situ. The wave velocity measurements based on planar interdigital transducers overcome the macroscopic size requirements of traditional time-of-flight and standing wave methods. The superheterodyne-scheme lock-in technique established in this article has replaced the commercial vector network analyzers for measuring surface acoustic wave velocity, enabling possible future applications with low power input and high phase stability. As the measurement setup can also be used for experimental teaching related to solid-state physics, this work provides detailed parameters and fabrication processes for surface acoustic wave devices and homemade stress cell. Related Articles | Metrics