2023, Volume 43

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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
Abstract149)      PDF (483KB)(250)      

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.

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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
Abstract186)      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. 

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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
Abstract264)      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. 

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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
Abstract782)      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 (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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Historic Origin of Quantum Entanglement in Particle Physics
Progress in Physics    2023, 43 (3): 57-67.   DOI: 10.13725/j.cnki.pip.2023.03.001
Abstract388)      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.

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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
Abstract246)      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.

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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
Abstract856)      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.
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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
Abstract448)      PDF (708KB)(647)      
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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
Abstract385)      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.

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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
Abstract300)      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. 

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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
Abstract229)      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: PnnmI4/mcmI4/mmm; (II) for RuP2: PnnmI41/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.

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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
Abstract374)      PDF (3042KB)(832)      

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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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
Abstract348)      PDF (7225KB)(398)      

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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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
Abstract273)      PDF (2445KB)(294)      

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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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
Abstract288)      PDF (88824KB)(251)      

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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Probing the Electronic Structure and Dimensionality Tuning of Ce-Based Heavy Fermion Materials
WU Yi , LI Peng , WU Zhong-zheng , FANG Yuan , LIU Yang
Progress in Physics    2022, 42 (3): 96-120.   DOI: 10.13725/j.cnki.pip.2022.03.002
Abstract286)      PDF (2002KB)(504)      

Heavy fermion compound is a classical type of correlated materials, encompassing unconventional superconductivity, strange metal, quantum criticality, magnetic order, heavy electronic states, correlated topological states, etc, in which 4f electrons play a critical role. With the advancement of high-resolution ARPES measurements and MBE thin film growth techniques, direct observation of the band dispersion and spectral weight of 4f electrons in momentum/energy space has become possible, providing spectroscopic insight for understanding correlated electronic states and novel quantum phenomena. In this review paper, we summarized the electronic studies of several typical heavy fermion compounds and thin films, including Ce-115 families, CuCu2Si2, CeRh6Ge4 and Ce films, etc. The experimental results provide direct evidence to understand the temperature evolution of heavy electronic states, energy/moment-dependent Kondo hybridization, the interplay of heavy electronic state with superconductivity, the competition between Kondo effect with other quantum states and the dimensionality tuning of 4f electrons.

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Development Status of Topological Superfluid in Ultracold Atoms
FENG Jian, ZHANG Wei-wei, LIN Liang-wei, CAI Qi-peng, ZHANG Yi-cai, LIU Chao-fei
Progress in Physics    2022, 42 (3): 67-95.   DOI: 10.13725/j.cnki.pip.2022.03.001
Abstract331)      PDF (1246KB)(590)      

The topological superfluid state is protected by the energy gap in the bulk, but it can accommodate the gapless Majorana fermions at the edge of the system. The Majorana fermions satisfy non-Abelian statistics and are protected by topology and have good stability, they can carry quantized information and can be used in the study of topological quantum computing. In recent years, theoretical work has predicted the possible topological superfluid states in various systems. Firstly, we introduce the topological superfluid in various optical lattice models. The ultracold atoms of optical lattice have good controllability and universality. It is an ideal model system to realize topological superfluid. Next, we introduce the topological superfluid under the control of spin orbit coupling. The spin orbit coupling effect is an important condition to induce the topological phase, and the artificial spin orbit coupling has been realized in the experiment. Which makes a breakthrough for the experimental observation of topological superfluid. With the improvement of experimental technology in recent years, the topological FFLO superfluid phase, which was difficult to observe in the experiment and ignored by people, has also become a research hotspot. Therefore, we next introduce the topological FFLO superfluid. In addition, we also introduce the progress in other aspects of topological superfluid, including topological superfluid induced by soliton, three-component topological superfluid, topological superfluid with large Chern number, and the high critical temperature of topological superfluid. In the experiment, how to detect and implement topological superfluid is the purpose and significance of our research. Therefore, we introduce the identification and implementation of topological superfluid at the end of the article.

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Quantum Radar Schemes with Enhanced Accuracy and Its Progress
LI Yong-qiang , REN Chang-liang
Progress in Physics    2022, 42 (2): 61-65.   DOI: 10.13725/j.cnki.pip.2022.02.003
Abstract382)      PDF (199KB)(611)      

As a matter of great concern, positioning tasks can be realized with the help of quantum technologies, and these quantum schemes exhibit advantages that are impossible in classical schemes. Several quantum radar schemes have been proposed, which give new insights for positioning tasks from the perspective of quantum information. This paper reviewed those proposed quantum radar schemes according to the basic concepts and classification Especially, three typical quantum schemes, quantum positioning, quantum illumination, and three-dimensional enhanced quantum radar, were introduced in principle, and analyzed their imperative problems.

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Photocurrent Mapping of Two-Dimensional Perovskite Solar Cell
ZHAO Xiao-xia, TIAN Wen-ming, SUN Zhong-gao, JIN Sheng-ye
Progress in Physics    2022, 42 (2): 54-60.   DOI: 10.13725/j.cnki.pip.2022.02.002
Abstract440)      PDF (751KB)(748)      

Developing an interplay between the local morphological character, optoelectronic properties and its local photovoltaic parameters in a perovskite thin film is essential for guiding the construction of highly-efficient perovskite solar cells (PSC). In this work, by using a laserscanned and time-resolved confocal microscopy coupled with a picoammeter detection module, we realize in-situ photoluminescence (PL) intensity, PL lifetime, and photocurrent mappings in a two-dimensional (2D) PSC. A significant negative correlation is found between photocurrent and PL intensity and PL lifetime imaging within grains of the perovskite polycrystalline film. We establish the correlation between local photovoltaic parameters, optoelectronic properties, and morphology character, which provides theoretical guidance for the optimization of PSC performance.

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Spin Hall Effect of Light and Its Applications in Measurements of Physical Parameters
LIU Shuo-qing , CHEN Shi-zhen , LUO Hai-lu
Progress in Physics    2022, 42 (2): 35-53.   DOI: 10.13725/j.cnki.pip.2022.02.001
Abstract1086)      PDF (8674KB)(1158)      

The spin Hall effect (SHE) of light refers to the transverse spin-dependent splitting of photons with opposite spin angular momentum after the beam passes through inhomogeneous media, in the direction perpendicular to the incident plane. It can be regarded as an analogue of the SHE in electronic systems, where the spin photons and the refractive index gradient replace the spin electrons and the electronic potential, respectively. Fundamentally, the SHE of light originates from the spin-orbit interaction of photons and depends mainly on two different geometric phases, namely, the spin redirection Rytov-Vlasimirskii-Berry phase in the momentum space and the Pancharatnam-Berry phase in the Stokes parameter space. Meanwhile, the SHE of light exhibits great sensitivity to the physical parameters, and combined with quantum weak measurements, has important application prospects in fields of physical parameters measurement and optical sensing. We briefly analyze the physical origin of the SHE of light, review its recent progress in different physical systems, and present its applications in measurements of physical parameters. Finally, the possible developing trends in optical analog computing, microscopy imaging, and quantum imaging are discussed.

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