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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
    Abstract2736)      PDF (58451KB)(2390)      
    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.
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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
    Abstract2565)      PDF (708KB)(3548)      
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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
    Abstract2456)      PDF (1284KB)(1865)      

    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.

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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
    Abstract2081)      PDF (5083KB)(1086)      

    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. 

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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
    Abstract1689)      PDF (4571KB)(1581)      

    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 (T) 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 T 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.

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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
    Abstract1537)      PDF (15745KB)(1540)      

    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.

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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
    Abstract1408)      PDF (452KB)(567)      

    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.

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    Hydrogen-Based Superconductors under High Pressures
    DU Ming-yang, ZHANG Zi-han, DUAN De-fang, CUI Tian
    Progress in Physics    2022, 42 (5): 184-192.   DOI: 10.13725/j.cnki.pip.2022.05.002
    Abstract1367)      PDF (3042KB)(3337)      

    Achieving room temperature superconductivity has always been the dream of mankind pursuing for a long time. Finding and synthesizing new materials with room temperature superconductivity is the ”Holy Grail” of condensed matter physics. Since the theoretical and experimental discovery of H3S and LaH10 with high superconducting critical temperature above 200 K, the hydrogen-based superconductors became the best candidate for achieving room temperature superconductivity, which is also one of the hot areas of multi-disciplinary research in physics, materials science etc. In this work, we outline the development history of superconductors, introduce several typical superconducting materials, focus on the current progress and challenges of hydrogen based superconductors under high pressures, discuss the design ideas of hydrogen based high-temperature superconductors in the middle and low pressure range, and look forward to the possibility of hydrogen-based superconductors with high critical temperature and even room temperature under low pressure or ambient pressure.

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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
    Abstract1350)      PDF (5051KB)(1922)      

    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. 

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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
    Abstract1275)      PDF (1055KB)(1386)      

    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.

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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
    Abstract1253)      PDF (9908KB)(1411)      

    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

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    Experimental Progress in Thermal Hall Conductivity Research on Strongly Correlated Electronic Systems
    XU Hao, CHENG Shu-fan, BAO Song , WEN Jin-sheng
    Progress in Physics    2022, 42 (5): 159-183.   DOI: 10.13725/j.cnki.pip.2022.05.001
    Abstract1247)      PDF (7225KB)(940)      

    Thermal Hall effect (THE) is to describe the phenomenon where heat carriers are deflected by an external magnetic field applied perpendicular to the heat flow, and thus the carriers gain transverse velocity, leading to a finite temperature gradient on the two sides orthogonal to the heat flow and field. THE is predicted to occur in systems with nontrivial Berry curvatures and thus can reveal topological properties, similar to the electrical Hall effect. However, THE is not limited to charge excitations as in the electrical Hall effect, but rather, to all kinds of excitations that are able to conduct heat, making it possible to explore the exotic properties in strongly correlated electronic systems, which are typically insulators. Therefore, THE is more universal than the electrical form and has become a powerful probe in detecting charge-neutral excitations, such as phonons and magnons. Moreover, there are some sources such as chiral phonons, which are beyond a simple nontrivial-Berry-curvature scenario, that can also give rise to THE; examining THE wherein will shed light on the complex microscopic mechanism hidden in materials. Despite these, heat signals are much weaker than electrical ones. Especially for measurements of the thermal Hall conductivity, it is often needed to collect weak signals on top of a large background. This makes measuring the THE challenging—but thanks to the sustained efforts of the community, this field is developing rapidly in recent years, with many interesting results on the measurements of the thermal Hall conductivity. In this review article, we try to summarize some of these exciting accomplishments, point out remaining outstanding issues, and suggest possible future directions. 

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    Thermal Transport Measurements in Strongly Correlated Electronic Systems 
    CHENG Shu-fan , XU Hao , BAO Song , WEN Jin-sheng
    Progress in Physics    2022, 42 (6): 207-231.   DOI: 10.13725/j.cnki.pip.2022.06.002
    Abstract1065)      PDF (11873KB)(876)      

    When taking into account the electronic correlations such as the onsite Coulomb repulsion and coupling between electrons, spins and orbitals, many fascinating novel quantum states beyond the free-electron framework can emerge, e.g., unconventional superconductiviity and quantum spin liquids. The understanding of these new states not only will expand the existing territory of our knowledge, but also likely lead to revolution in quantum science and technology. Therefore, studying the strongly correlated physics is a cutting-edge theme in condensed matter physics. The parent state of cuprate high-temperature superconductors is a Mott insulator, an insulating state due to the strong electronic correlation, whereas the band theory predicts it to be metallic. Due to the Coulomb gap in Mott insulators, the charge degree of freedom is often frozen, which makes electrical transport measurements inapplicable. As a probe sensitive to the elementary excitations of quasiparticles not limited to electrons, but also including magnons, spinons, as well as phonons, thermal transport measurements play an important role in the study of strongly correlated electronic systems. In this paper, we review some of the recent interesting results on unconventional superconductors, heavy fermions and quantum spin liquids utilizing the longitudinal thermal transport measurements, complimentary to our recent review article on the progress of the transverse thermal conductivity measurements on the thermal Hall effect. 

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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
    Abstract1062)      PDF (837KB)(1226)      

    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. 

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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
    Abstract998)      PDF (4272KB)(747)      

    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. 

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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
    Abstract989)      PDF (2466KB)(834)      
    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
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    Research Status of Interlayer Magnetism for Bilayer Transition Metal Trihalides#br#
    SI Jun-shan , YANG Zhi-xiong , ZHANG Wei-bing
    Progress in Physics    2022, 42 (4): 147-157.   DOI: 10.13725/j.cnki.pip.2022.04.002
    Abstract970)      PDF (2445KB)(1019)      
    Two-dimensional magnetic materials are the focus of condensed matter physics. Recent experiments have found that bulk CrI3 shows an interlayer ferromagnetic order, whereas its bilayer possesses interlayer antiferromagnetism, which shows the quantum confinement effect and potential device applications, and has attracted widespread attention. Many studies have shown that interlayer magnetism is closely related to stacking order, but it is still controversial. This paper reviews the main research on the interlayer magnetism of bilayer transition metal trihalides and its application. Firstly, we introduced the relationship between the interlayer magnetism and stacking order, and then pointed out the density functional theory’s challenges in describing the interlayer magnetic mechanism. Finally, we expounded on the interlayer magnetism-related device applications and proposed the future research direction.
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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
    Abstract965)      PDF (8816KB)(1215)      
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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
    Abstract958)      PDF (2081KB)(444)      

    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

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    Finite-Temperature Tensor Renormalization Group Method and the Applications to Frustrated Quantum Magnets#br#
    LI Han, LI Wei
    Progress in Physics    2022, 42 (4): 121-146.   DOI: 10.13725/j.cnki.pip.2022.04.001
    Abstract865)      PDF (88824KB)(588)      

    The exotic spin states and quantum effects in frustrated magnets have attracted intensive research interest in recent years, which also have intimate connections with hightemperature superconductivity and topological quantum computing, etc. Experimentally, people have focused on typical spin liquid candidate materials including the triangular-, kagomeand Kitaev honeycomb-lattice frustrated magnets. However, it constitutes a very challenging many-body problem to clarify the quantum states and phase transitions therein. Recently, we point out that it is possible to establish a protocol for understanding and explaining experiments of frustrated magnets in an unbiased manner. By employing the finite-temperature tensor renormalization group methods, we carry out accurate calculations and analyses of thermodynamic properties, determine the microscopic spin model of the frustrated magnets, and make further theoretical predictions. Below, we firstly introduce the recently proposed tensor renormalization group (TRG) methods, including the linear and exponential TRG, and discuss their applications on the triangular-lattice quantum Ising magnet TmMgGaO4 and the Kitaevhoneycomb material α-RuCl3. We demonstrate that the finite-temperature TRG approaches shed light on the study of spin liquid candidate materials, and could facilitate cutting-edge research in the field of strongly correlated quantum systems.

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