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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 （2125）      PDF （58451KB）（2062）       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 （1763）      PDF （1284KB）（1546）       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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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 （658）      PDF （483KB）（1508）       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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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 （947）      PDF （5051KB）（1317）       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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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 （1424）      PDF （4571KB）（1282）       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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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 （876）      PDF （9908KB）（1072）       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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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 （652）      PDF （9233KB）（1024）       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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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 （800）      PDF （837KB）（968）       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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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 （632）      PDF （3411KB）（843）       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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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 （1156）      PDF （5083KB）（816）       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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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 （573）      PDF （8816KB）（751）       Related Articles | Metrics

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Halide Perovskite Single Crystals and Photodetectors: Research Progress and Challenges  SUN Yue, HUANG Xiao-rui , HE Sheng-rong, XING Jun Progress in Physics    2024, 44 (5): 209-242.   DOI: 10.13725/j.cnki.pip.2024.05.001 Abstract （492）      PDF （15745KB）（708）       In recent years, metal halide perovskite materials have made great scientific progress in the field of light detection, photoelectric conversion, and light emission due to their excellent optical and electrical properties (such as high absorption coefficient, long carrier diffusion length, small exciton binding energy, high defect tolerance, and adjustable band gap, etc.), and low-cost solution preparation process. In recent decades, scientific research on the preparation and optimization of perovskite single crystals has been promoted driven by their advantages compared to polycrystalline perovskite films. These advantages include longer carrier lifetime, higher carrier mobility, longer diffusion length, and lower trap density. High-quality halide perovskite single crystals have been widely used in important applications such as photodetection. This review focuses on the recent advancements in photodetector technology using various forms and chemical compositions of halide perovskite single crystals, including single crystal bulks and single crystal thin films. Firstly, we systematically review the preparation and optimization progress of halide perovskite single crystals, with a focus on the latest progress in triple cations hybrid perovskite single crystals. After that, a comprehensive introduction was given to the research status of various types of photodetectors based on perovskite single crystals. Finally, the current challenges and future development prospects in the research field of halide perovskite single crystal photodetector are summarized in order to promote rapid progress and development 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 （457）      PDF （4278KB）（674）       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

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Progress on High-Pressure Structure and Properties of Phosphorus and Phosphide HUANG Ye-hua, GUO Zhen-yuan, LI Jun-kai, YANG Xin, GOU Hui-yang Progress in Physics    2024, 44 (3): 123-135.   DOI: 10.13725/j.cnki.pip.2024.03.003 Abstract （386）      PDF （6131KB）（616）       Phosphorus，a group V non-metallic element, exhibits a unique electronic structure along with excellent optical, electrical and mechanical properties, and has a wide range of application prospects. Recent studies have demonstrated that phosphorus and phosphides are easily affected and regulated by external fields and have rich physical and chemical properties under high pressure. In addition, the unique structure and electronic properties of phosphorus and phosphides give them many physical properties that differ from those of traditional materials. Therefore, the use of high pressure to induce structural transformation and superconducting transformation in phosphorus and phosphides has become the focus of high-pressure research. In this paper, the structural, electrical, and optical responses of black phosphorus, germanium phosphide, and arsenic phosphide under high-pressure conditions are reviewed and discussed. Furthermore, we also explore the structure-activity relationships between the structures and physical properties and forecast the future research directions of phosphides under high pressure. Related Articles | Metrics

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The Research Progress on One-Dimensional Spin-Orbit Coupled Fermi Gas CAI Qi-peng, ZHANG Wei-wei, LIN Liang-wei, XU Yi-guang, CHEN Zi-xuan, WANG Xiao-sheng, YU Hai-peng, FANG Xiao-hong, ZHANG Yi-cai, LIU Chao-fei Progress in Physics    2024, 44 (4): 157-182.   DOI: 10.13725/j.cnki.pip.2024.04.001 Abstract （337）      PDF （3164KB）（597）       In ultracold Fermi gases, by adjusting the strength of spin orbit coupling to match Fermi energy, many novel quantum effects can be generated. In the past few decades, scholars have conducted extensive theoretical and experimental research on Fermi gases induced by one-dimensional spin orbit coupling. Compared with high-dimensional spin orbit coupling, one-dimensional spin orbit coupling, although relatively simple, is the most reliable and feasible tool for exploring basic quantum physical phenomena in experiments. This paper systematically summarizes the interesting physical phenomena of Fermi gas under one-dimensional spin orbit coupling in theoretical work. Including theoretical research on dynamic oscillation and soliton effect, topological superfluid, Majorana edge state, ferromagnetic phase transition, and quantum phase. How to achieve spin orbit coupling and observe singular phenomena in experiments is a hot and difficult research topic. We summarize several common experimental schemes and detection methods. Finally, we look forward to the research on Fermi gas induced by one-dimensional spin orbit coupling. One dimensional spin orbit coupling can provide reference for abecedarians and contribute to the study of multi body system regulated by spin orbit coupling. This paper aims to provide a reference for abecedarians in cold atomic physics to gain a deeper understanding of the physical mechanisms of multi-body systems under spin orbit coupling. 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 （698）      PDF （4272KB）（579）       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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Working Memory: Mechanisms and Modeling Approaches YANG Fan, QIAN Rui-xin, WANG Tao Progress in Physics    2024, 44 (5): 243-258.   DOI: 10.13725/j.cnki.pip.2024.05.002 Abstract （300）      PDF （2967KB）（544）       Working memory, a cornerstone of human cognition, allows us to temporarily hold and manipulate information. The delayed response experiment is a fundamental tool for understanding working memory. By inserting a delay between the presentation of stimuli and the behavioral decision, researchers can probe the neural mechanisms underlying information maintenance and manipulation during this delay period. This review delves into the delayed response paradigm and introduces attractor dynamics as a potential mechanism for working memory function. We then systematically explore two common methods for analyzing working memory networks: trajectory tracking, and energy landscape and flux theory. Finally, we summarize the key features of these two dynamical approaches and provide an outlook for future directions of working memory research. 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 （543）      PDF （6736KB）（528）       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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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 （656）      PDF （2466KB）（520）       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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Progress in Thin-Layer Quantization WANG Yonglong, DU Long Progress in Physics    2024, 44 (1): 9-18.   DOI: 10.13725/j.cnki.pip.2024.01.002 Abstract （438）      PDF （4146KB）（508）       With the rapid development of microtechnology, the low-dimensional materials are fabricated with nontrivial topological structures, and then the action of geometric properties on the effective dynamics receives increasing attention. It is an effective theory that the quantum mechanics of low-dimensional curved systems can be given by using the thin-layer quantization approach, in which the geometric potential and the geometric momentum have been demonstrated experimentally. In the present paper, the thin-layer quantization formalism is first recalled, its fundamental calculation framework is first clarified, and the geometric quantum effects result from the diffeomorphism transformation and the rotation transformation connecting the local frames of different points. The results are helpful to understand the gravitational gauge and emerging gauge, and to image the geometries implied in the artificial gauge. In the particular quantum systems, the novel physical phenomena are briefly recalled that are induced by geometry, such as resonation tunneling, quantum block, quantum Hall effect, quantum Hall viscosity, quantum spin Hall effect, effective monopole magnetic field and so on. The results will shed light from a different angle on the relationships between the geometry and the novel physical phenomenon. Related Articles | Metrics