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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 （856）      PDF （58451KB）（1032）       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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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 （782）      PDF （4571KB）（397）       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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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 （448）      PDF （708KB）（647）       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 （388）      PDF （1284KB）（474）       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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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 （385）      PDF （1055KB）（283）       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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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 Abstract （300）      PDF （11873KB）（360）       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.  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 （264）      PDF （5051KB）（374）       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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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 （246）      PDF （9233KB）（522）       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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Pressure-Induced Superconducting and Topological Phase Transitions in the Ru X 2 ( X=P, As, Sb) Family Compounds CHEN Qun , WU Jue-fei , WANG Xiao-meng , DING Chi, HUANG Tian-heng , LU Qing , SUN Jian Progress in Physics    2022, 42 (6): 195-206.   DOI: 10.13725/j.cnki.pip.2022.06.001 Abstract （229）      PDF （9142KB）（260）       RuSb2, as a sister material of thermoelectric material FeSb2, has been extensively studied focusing on the comparisons with FeSb2, however, the properties of RuSb2 under pressure have not been surveyed thoroughly yet. In this work, we studied the properties of RuSb2 under pressure and explored the similarities and differences of crystal and electronic structures between the Ru-pnictides partners RuP2 and RuAs2. Using the crystal structures search method together with first-principles calculations, we found that this family undergoes a serial of structural phase transitions: (I) For RuSb2: Pnnm → I4/mcm → I4/mmm; (II) for RuP2: Pnnm → I41/amd → Cmcm; (III) for RuAs2: Pnnm → P-62m. The newly found five phases are all energetically and dynamically stable at high-pressure and exhibit metallic properties. The four high pressure phases of RuSb2 and RuP2 can be quenched to zero pressure. The superconducting transition temperatures of I4/mcm and I4/mmm phases of RuSb2 and I41/amd and Cmcm phase of RuP2 are predicted to be approximately 7.3 K, 10.9 K, 13.0 K, and 10.1 K at 0 GPa, respectively. In addition, the I4/mcm and I4/mmm phases of RuSb2 and the I41/amd phase of RuP2 exhibit non-trivial topological properties. Our studies illustrate that pressure is an effective way to tune the structural, electronic, and superconducting behavior of the Ru-pnictides compounds. 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 （186）      PDF （837KB）（411）       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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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 （150）      PDF （483KB）（251）       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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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 （98）      PDF （4272KB）（143）       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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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 （94）      PDF （452KB）（114）       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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Potential Impurity Effect in Twisted Bilayer Graphene LIU Ze-zhong , WANG Da Progress in Physics    2023, 43 (5): 151-160.   DOI: 10.13725/j.cnki.pip.2023.05.003 Abstract （55）      PDF （5362KB）（75）       Flat band has attracted more and more interest in recent years, motivated by its discovery in twisted bilayer graphene (TBG). In this work, we report our study of the impurity effect on this flat band system, which is an important issue for real materials. Employing the Lanczos recursive method, we solve the local density of states (LDOS) around a potential impurity. We find for large impurity size, a series of bound states are formed inside the impurity, and the flat band peak in LDOS is suppressed near the impurity boundary and shifted by the impurity potential deep inside the impurity. As the impurity size becomes smaller, the effect on the flat band becomes weaker, as anticipated from the large scale of the underlying Wannier function. This property distinguishes with the usual flat band systems with small localized Wannier orbitals, and indicates the flat band in TBG is more stable against small-size impurities.  Related Articles | Metrics