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TOPICAL REVIEW — Celebrating 30 Years of Chinese Physics B

 Select Editorial: Celebrating the 30 Wonderful Year Journey of Chinese Physics B Hong-Jun Gao(高鸿钧), and Qihua Xiong(熊启华) Chin. Phys. B, 2022, 31 (12): 120101.   DOI: 10.1088/1674-1056/acaa95 Abstract （61）      PDF （195KB）（125）       The year 2022 marks the 30th anniversary of Chinese Physics B. This editorial provides a brief history of the journal and introduces the anniversary theme collection comprising over 30 invited reviews and perspective articles from renowned scholars in various branches of physics.
 Select Mottness, phase string, and high-Tc superconductivity Jing-Yu Zhao(赵靖宇) and Zheng-Yu Weng(翁征宇) Chin. Phys. B, 2022, 31 (8): 087104.   DOI: 10.1088/1674-1056/ac7a14 Abstract （153）   HTML （2）    PDF （969KB）（117）       It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces, characterized by a nonintegrable phase factor that an elementary particle of charge $q$ acquires from $A$ to $B$ points: $P \exp \left( \text{i} \frac q {\hbar c}\int_A^B A_{\mu}\text{d} x^{\mu}\right),$ where $A_{\mu}$ is the gauge potential and $P$ stands for path ordering. In a many-body system of strongly correlated electrons, if the so-called Mott gap is opened up by interaction, the corresponding Hilbert space will be fundamentally changed. A novel nonintegrable phase factor known as phase-string will appear and replace the conventional Fermi statistics to dictate the low-lying physics. Protected by the Mott gap, which is clearly identified in the high-$T_{\rm c}$ cuprate with a magnitude $> 1.5$ eV, such a singular phase factor can enforce a fractionalization of the electrons, leading to a dual world of exotic elementary particles with a topological gauge structure. A non-Fermi-liquid "parent" state will emerge, in which the gapless Landau quasiparticle is only partially robust around the so-called Fermi arc regions, while the main dynamics are dominated by two types of gapped spinons. Antiferromagnetism, superconductivity, and a Fermi liquid with full Fermi surface can be regarded as the low-temperature instabilities of this new parent state. Both numerics and experiments provide direct evidence for such an emergent physics of the Mottness, which lies in the core of a high-$T_{\rm c}$ superconducting mechanism.
 Select A sport and a pastime: Model design and computation in quantum many-body systems Gaopei Pan(潘高培), Weilun Jiang(姜伟伦), and Zi Yang Meng(孟子杨) Chin. Phys. B, 2022, 31 (12): 127101.   DOI: 10.1088/1674-1056/aca083 Abstract （81）      PDF （6474KB）（105）       We summarize the recent developments in the model design and computation for a few representative quantum many-body systems, encompassing quantum critical metals beyond the Hertz-Millis-Moriya framework with pseudogap and superconductivity, SYK non-Fermi-liquid with self-tuned quantum criticality and fluctuation induced superconductivity, and the flat-band quantum Moiré lattice models in continuum where the interplay of quantum geometry of flat-band wave function and the long-range Coulomb interactions gives rise to novel insulating phases at integer fillings and superconductivity away from them. Although the narrative choreography seems simple, we show how important the appropriate model design and their tailor-made algorithmic developments - in other words, the scientific imagination inspired by the corresponding fast experimental developments in the aforementioned systems - compel us to invent and discover new knowledge and insights in the sport and pastime of quantum many-body research.
 Select Computational studies on magnetism and ferroelectricity Ke Xu(徐可), Junsheng Feng(冯俊生), and Hongjun Xiang(向红军) Chin. Phys. B, 2022, 31 (9): 097505.   DOI: 10.1088/1674-1056/ac7b1b Abstract （138）   HTML （2）    PDF （2190KB）（141）       Magnetics, ferroelectrics, and multiferroics have attracted great attentions because they are not only extremely important for investigating fundamental physics, but also have important applications in information technology. Here, recent computational studies on magnetism and ferroelectricity are reviewed. We first give a brief introduction to magnets, ferroelectrics, and multiferroics. Then, theoretical models and corresponding computational methods for investigating these materials are presented. In particular, a new method for computing the linear magnetoelectric coupling tensor without applying an external field in the first principle calculations is proposed for the first time. The functionalities of our home-made Property Analysis and Simulation Package for materials (PASP) and its applications in the field of magnetism and ferroelectricity are discussed. Finally, we summarize this review and give a perspective on possible directions of future computational studies on magnetism and ferroelectricity.
 Select Progress and challenges in magnetic skyrmionics Haifeng Du(杜海峰) and Xiangrong Wang(王向荣) Chin. Phys. B, 2022, 31 (8): 087507.   DOI: 10.1088/1674-1056/ac754f Abstract （129）   HTML （4）    PDF （659KB）（120）       Magnetic skyrmions are two-dimensional localized topological spin-structures characterized by the skyrmion number that measures the number of times of spins wrapping the Bloch sphere. Skyrmions behave like particles under an external stimulus and are promising information carriers. Skyrmions can exist as an isolated object as well as skyrmion condensates in crystal structures, helical/conical states, mazes or irregular stripy states with emergent electromagnetic fields. Thus, skyrmions provide a nice platform for studying fundamental physics, other than its applications in spintronics. In this perspective, we briefly review some recent progress in the field and present an outlook of the fundamental challenges in device applications.
 Select Exploring Majorana zero modes in iron-based superconductors Geng Li(李更), Shiyu Zhu(朱诗雨), Peng Fan(范朋), Lu Cao(曹路), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2022, 31 (8): 080301.   DOI: 10.1088/1674-1056/ac70c3 Abstract （187）   HTML （0）    PDF （4673KB）（111）       Majorana zero modes (MZMs) are Majorana-fermion-like quasiparticles existing in crystals or hybrid platforms with topologically non-trivial electronic structures. They obey non-Abelian braiding statistics and are considered promising to realize topological quantum computing. Discovery of MZM in the vortices of the iron-based superconductors (IBSs) has recently fueled the Majorana research in a way which not only removes the material barrier requiring construction of complicated hybrid artificial structures, but also enables observation of pure MZMs under higher temperatures. So far, MZMs have been observed in iron-based superconductors including FeTe0.55Se0.45, (Li0.84Fe0.16)OHFeSe, CaKFe4As4, and LiFeAs. In this topical review, we present an overview of the recent STM studies on the MZMs in IBSs. We start with the observation of MZMs in the vortices in FeTe0.55Se0.45 and discuss the pros and cons of FeTe0.55Se0.45 compared with other platforms. We then review the following up discovery of MZMs in vortices of CaKFe4As4, impurity-assisted vortices of LiFeAs, and quantum anomalous vortices in FeTe0.55Se0.45, illustrating the pathway of the developments of MZM research in IBSs. Finally, we give perspective on future experimental works in this field.
 Select Superconductivity and unconventional density waves in vanadium-based kagome materials AV3Sb5 Hui Chen(陈辉), Bin Hu(胡彬), Yuhan Ye(耶郁晗), Haitao Yang(杨海涛), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2022, 31 (9): 097405.   DOI: 10.1088/1674-1056/ac7f95 Abstract （174）   HTML （4）    PDF （6290KB）（78）       Recently, the discovery of vanadium-based kagome metal AV3Sb5 (A= K, Rb, Cs) has attracted great interest in the field of superconductivity due to the coexistence of superconductivity, non-trivial surface state and multiple density waves. In this topical review, we present recent works of superconductivity and unconventional density waves in vanadium-based kagome materials AV3Sb5. We start with the unconventional charge density waves, which are thought to correlate to the time-reversal symmetry-breaking orders and the unconventional anomalous Hall effects in AV3Sb5. Then we discuss the superconductivity and the topological band structure. Next, we review the competition between the superconductivity and charge density waves under different conditions of pressure, chemical doping, thickness, and strains. Finally, the experimental evidence of pseudogap pair density wave is discussed.
 Select Recent advances in quasi-2D superconductors via organic molecule intercalation Mengzhu Shi(石孟竹), Baolei Kang(康宝蕾), Tao Wu(吴涛), and Xianhui Chen(陈仙辉) Chin. Phys. B, 2022, 31 (10): 107403.   DOI: 10.1088/1674-1056/ac8e9d Abstract （91）   HTML （0）    PDF （2576KB）（54）       Superconductivity at the 2D limit shows emergent novel quantum phenomena, including anomalously enhanced Hc2, quantum metallic states and quantum Griffiths singularity, which has attracted much attention in the field of condensed matter physics. In this article, we focus on new advances in quasi-2D superconductors in the bulk phase using an organic molecular electrochemical intercalation method. The enhanced superconductivity and emergent pseudogap behavior in these quasi-2D superconductors are summarized with a further prospect.
 Select Molecular beam epitaxy growth of quantum devices Ke He(何珂) Chin. Phys. B, 2022, 31 (12): 126804.   DOI: 10.1088/1674-1056/aca6d3 Abstract （68）      PDF （1803KB）（61）       The inherent fragility and surface/interface-sensitivity of quantum devices demand fabrication techniques under very clean environment. Here, I briefly introduces several techniques based on molecular beam epitaxy growth on pre-patterned substrates which enable us to directly prepare in-plane nanostructures and heterostructures in ultrahigh vacuum. The molecular beam epitaxy-based fabrication techniques are especially useful in constructing the high-quality devices and circuits for solid-state quantum computing in a scalable way.
 Select Recent advances of defect-induced spin and valley polarized states in graphene Yu Zhang(张钰), Liangguang Jia(贾亮广), Yaoyao Chen(陈瑶瑶), Lin He(何林), and Yeliang Wang(王业亮) Chin. Phys. B, 2022, 31 (8): 087301.   DOI: 10.1088/1674-1056/ac70c4 Abstract （155）   HTML （4）    PDF （2213KB）（69）       Electrons in graphene have fourfold spin and valley degeneracies owing to the unique bipartite honeycomb lattice and an extremely weak spin-orbit coupling, which can support a series of broken symmetry states. Atomic-scale defects in graphene are expected to lift these degenerate degrees of freedom at the nanoscale, and hence, lead to rich quantum states, highlighting promising directions for spintronics and valleytronics. In this article, we mainly review the recent scanning tunneling microscopy (STM) advances on the spin and/or valley polarized states induced by an individual atomic-scale defect in graphene, including a single-carbon vacancy, a nitrogen-atom dopant, and a hydrogen-atom chemisorption. Lastly, we give a perspective in this field.
 Select Magnetic van der Waals materials: Synthesis, structure, magnetism, and their potential applications Zhongchong Lin(林中冲), Yuxuan Peng(彭宇轩), Baochun Wu(吴葆春), Changsheng Wang(王常生), Zhaochu Luo(罗昭初), and Jinbo Yang(杨金波) Chin. Phys. B, 2022, 31 (8): 087506.   DOI: 10.1088/1674-1056/ac6eed Abstract （124）   HTML （1）    PDF （2684KB）（119）       As the family of magnetic materials is rapidly growing, two-dimensional (2D) van der Waals (vdW) magnets have attracted increasing attention as a platform to explore fundamental physical problems of magnetism and their potential applications. This paper reviews the recent progress on emergent vdW magnetic compounds and their potential applications in devices. First, we summarize the current vdW magnetic materials and their synthetic methods. Then, we focus on their structure and the modulation of magnetic properties by analyzing the representative vdW magnetic materials with different magnetic structures. In addition, we pay attention to the heterostructures of vdW magnetic materials, which are expected to produce revolutionary applications of magnetism-related devices. To motivate the researchers in this area, we finally provide the challenges and outlook on 2D vdW magnetism.
 Select From microelectronics to spintronics and magnonics Xiu-Feng Han(韩秀峰), Cai-Hua Wan(万蔡华), Hao Wu(吴昊), Chen-Yang Guo(郭晨阳), Ping Tang(唐萍), Zheng-Ren Yan(严政人), Yao-Wen Xing(邢耀文), Wen-Qing He(何文卿), and Guo-Qiang Yu(于国强) Chin. Phys. B, 2022, 31 (11): 117504.   DOI: 10.1088/1674-1056/ac9048 Abstract （137）   HTML （5）    PDF （2474KB）（126）       In this review, the recent developments in microelectronics, spintronics, and magnonics have been summarized and compared. Firstly, the history of the spintronics has been briefly reviewed. Moreover, the recent development of magnonics such as magnon-mediated current drag effect (MCDE), magnon valve effect (MVE), magnon junction effect (MJE), magnon blocking effect (MBE), magnon-mediated nonlocal spin Hall magnetoresistance (MNSMR), magnon-transfer torque (MTT) effect, and magnon resonant tunneling (MRT) effect, magnon skin effect (MSE), etc., existing in magnon junctions or magnon heterojunctions, have been summarized and their potential applications in memory and logic devices, etc., are prospected, from which we can see a promising future for spintronics and magnonics beyond micro-electronics.
 Select Epitaxy of III-nitrides on two-dimensional materials and its applications Yu Xu(徐俞), Jianfeng Wang(王建峰), Bing Cao(曹冰), and Ke Xu(徐科) Chin. Phys. B, 2022, 31 (11): 117702.   DOI: 10.1088/1674-1056/ac921f Abstract （63）   HTML （1）    PDF （1726KB）（58）       III-nitride semiconductor materials have excellent optoelectronic properties, mechanical properties, and chemical stability, which have important applications in the field of optoelectronics and microelectronics. Two-dimensional (2D) materials have been widely focused in recent years due to their peculiar properties. With the property of weak bonding between layers of 2D materials, the growth of III-nitrides on 2D materials has been proposed to solve the mismatch problem caused by heterogeneous epitaxy and to develop substrate stripping techniques to obtain high-quality, low-cost nitride materials for high-quality nitride devices and their extension in the field of flexible devices. In this progress report, the main methods for the preparation of 2D materials, and the recent progress and applications of different techniques for the growth of III-nitrides based on 2D materials are reviewed.
 Select Advances and challenges in DFT-based energy materials design Jun Kang(康俊), Xie Zhang(张燮), and Su-Huai Wei(魏苏淮) Chin. Phys. B, 2022, 31 (10): 107105.   DOI: 10.1088/1674-1056/ac89d7 Abstract （158）   HTML （0）    PDF （1641KB）（94）       The growing worldwide energy needs call for developing novel materials for energy applications. Ab initio density functional theory (DFT) calculations allow the understanding and prediction of material properties at the atomic scale, thus, play an important role in energy materials design. Due to the fast progress of computer power and development of calculation methodologies, DFT-based calculations have greatly improved their predictive power, and are now leading to a paradigm shift towards theory-driven materials design. The aim of this perspective is to introduce the advances in DFT calculations which accelerate energy materials design. We first present state-of-the-art DFT methods for accurate simulation of various key properties of energy materials. Then we show examples of how these advances lead to the discovery of new energy materials for photovoltaic, photocatalytic, thermoelectric, and battery applications. The challenges and future research directions in computational design of energy materials are highlighted at the end.
 Select Anionic redox reaction mechanism in Na-ion batteries Xueyan Hou(侯雪妍), Xiaohui Rong(容晓晖), Yaxiang Lu(陆雅翔), and Yong-Sheng Hu(胡勇胜) Chin. Phys. B, 2022, 31 (9): 098801.   DOI: 10.1088/1674-1056/ac81ab Abstract （110）   HTML （0）    PDF （2096KB）（59）       Na-ion batteries (NIBs), as one of the next-generation rechargeable battery systems, hold great potential in large-scale energy storage applications owing to the abundance and costeffectiveness of sodium resources. Despite the extensive exploration of electrode materials, the relatively low attainable capacity of NIBs hinders their practical application. In recent years, the anionic redox reaction (ARR) in NIBs has been emerging as a new paradigm to deliver extra capacity and thus offers an opportunity to break through the intrinsic energy density limit. In this review, the fundamental investigation of the ARR mechanism and the latest exploration of cathode materials are summarized, in order to highlight the significance of reversible anionic redox and suggest prospective developing directions.
 Select Understanding the battery safety improvement enabled by a quasi-solid-state battery design Luyu Gan(甘露雨), Rusong Chen(陈汝颂), Xiqian Yu(禹习谦), and Hong Li(李泓) Chin. Phys. B, 2022, 31 (11): 118202.   DOI: 10.1088/1674-1056/ac9221 Abstract （80）   HTML （0）    PDF （916KB）（51）       The rapid development of lithium-ion batteries (LIBs) is faced with challenge of its safety bottleneck, calling for design and chemistry innovations. Among the proposed strategies, the development of solid-state batteries (SSBs) seems the most promising solution, but to date no practical SSB has been in large-scale application. Practical safety performance of SSBs is also challenged. In this article, a brief review on LIB safety issue is made and the safety short boards of LIBs are emphasized. A systematic safety design in quasi-SSB chemistry is proposed to conquer the intrinsic safety weak points of LIBs and the effects are accessed based on existing studies. It is believed that a systematic and targeted solution in SSB chemistry design can effectively improve the battery safety, promoting larger-scale application of LIBs.
 Select Recent advances of interface engineering in inverted perovskite solar cells Shiqi Yu(余诗琪), Zhuang Xiong(熊壮), Zhenhan Wang(王振涵), Haitao Zhou(周海涛), Fei Ma(马飞), Zihan Qu(瞿子涵), Yang Zhao(赵洋), Xinbo Chu(楚新波), and Jingbi You(游经碧) Chin. Phys. B, 2022, 31 (10): 107307.   DOI: 10.1088/1674-1056/ac8e9f Abstract （109）   HTML （0）    PDF （8177KB）（49）       Perovskite solar cells (PSCs) have witnessed great achievement in the past decade. Most of previous researches focus on the n—i—p structure of PSCs with ultra-high efficiency. While the n—i—p devices usually used the unstable charge transport layers, such as the hygroscopic doped spiro-OMeTAD, which affect the long-term stability. The inverted device with the p—i—n structure owns better stability when using stable undoped organic molecular or metal oxide materials. There are significant progresses in inverted PSCs, most of them related to charge transport or interface engineering. In this review, we will mainly summarize the inverted PSCs progresses related to the interface engineering. After that, we prospect the future direction on inverted PSCs.
 Select Research progress of Pt and Pt-based cathode electrocatalysts for proton-exchange membrane fuel cells Ni Suo(索妮), Longsheng Cao(曹龙生), Xiaoping Qin(秦晓平), and Zhigang Shao(邵志刚) Chin. Phys. B, 2022, 31 (12): 128108.   DOI: 10.1088/1674-1056/aca081 Abstract （50）      PDF （4748KB）（29）       Proton-exchange membrane fuel cells (PEMFCs) have been widely used commercially to solve the energy crisis and environmental pollution. The oxygen reduction reaction (ORR) at the cathode is the rate-determining step in PEMFCs. Platinum (Pt) catalysts are used to accelerate the ORR kinetics. Pt's scarcity, high cost, and instability in an acidic environment at high potentials seriously hinder the commercialization of PEMFCs. Therefore, studies should explore electrocatalysts with high catalytic activity, enhanced stability, and low-Pt loading. This review briefly introduces the research progress on Pt and Pt-based ORR electrocatalysts for PEMFCs, including anticorrosion catalyst supports, Pt, and Pt-based alloy electrocatalysts. Advanced preparation technology and material characterization of Pt-based ORR electrocatalysts are necessary to improve the performance and corresponding reaction mechanisms.
 Select Ultrafast Coulomb explosion imaging of molecules and molecular clusters Xiaokai Li(李孝开), Xitao Yu(余西涛), Pan Ma(马盼), Xinning Zhao(赵欣宁), Chuncheng Wang(王春成), Sizuo Luo(罗嗣佐), and Dajun Ding(丁大军) Chin. Phys. B, 2022, 31 (10): 103304.   DOI: 10.1088/1674-1056/ac89df Abstract （91）   HTML （2）    PDF （8911KB）（72）       Taking an image of their structure and a movie of their dynamics of small quantum systems have always been a dream of physicists and chemists. Laser-induced Coulomb explosion imaging (CEI) provides a great opportunity to make this dream a reality for small molecules or their aggregation —— clusters. The method is unique for identifying the atomic locations with ångstrom spatial resolution and capturing the structural evolution with a femtosecond time scale, in particular for imaging transient state products. This review summarizes the determination of three-dimensional equilibrium geometry of molecules and molecular cluster system through the reconstruction from the fragments momenta, and also shows that the dissociation dynamics on the complex potential energy surface can be tracked in real-time with the ultrafast CEI (UCEI). Furthermore, the detailed measurement and analysis procedures of the CEI, theoretical methods, exemplary results, and future perspectives of the technique are described.
 Select Atomic structure and collision dynamics with highly charged ions Xinwen Ma(马新文), Shaofeng Zhang(张少锋), Weiqiang Wen(汶伟强), Zhongkui Huang(黄忠魁), Zhimin Hu(胡智民), Dalong Guo(郭大龙), Junwen Gao(高俊文), Bennaceur Najjari, Shenyue Xu(许慎跃), Shuncheng Yan(闫顺成), Ke Yao(姚科), Ruitian Zhang(张瑞田), Yong Gao(高永), and Xiaolong Zhu(朱小龙) Chin. Phys. B, 2022, 31 (9): 093401.   DOI: 10.1088/1674-1056/ac8736 Abstract （121）   HTML （6）    PDF （3242KB）（73）       The research progresses on the investigations of atomic structure and collision dynamics with highly charged ions based on the heavy ion storage rings and electron ion beam traps in recent 20 years are reviewed. The structure part covers test of quantum electrodynamics and electron correlation in strong Coulomb field studied through dielectronic recombination spectroscopy and VUV/x-ray spectroscopy. The collision dynamics part includes charge exchange dynamics in ion-atom collisions mainly in Bohr velocity region, ion-induced fragmentation mechanisms of molecules, hydrogen-bound and van de Waals bound clusters, interference, and phase information observed in ion-atom/molecule collisions. With this achievements, two aspects of theoretical studies related to low energy and relativistic energy collisions are presented. The applications of data relevant to key atomic processes like dielectronic recombination and charge exchanges involving highly charged ions are discussed. At the end of this review, some future prospects of research related to highly charged ions are proposed.