Content of SPECIAL TOPIC — Recent progress on kagome metals and superconductors in our journal

Published in last 1 year |  In last 2 years |  In last 3 years |  All Please wait a minute... For selected: Download citations EndNote Ris BibTeX Toggle thumbnails Select Observation of a long-range unidirectional charge density wave in kagome superconductor KV3Sb5 Xingwei Shi(石兴伟), Xiao Liu(刘潇), Geng Li(李更), Zhen Zhao(赵振), Haitao Yang(杨海涛), Xiao Lin(林晓), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2025, 34 (7): 077101.   DOI: 10.1088/1674-1056/add7ad Abstract （150）   HTML （0）    PDF （5854KB）（269）       Knowledge map    The interplay between 2$a_{0}\times2a_{0}$ charge density wave (CDW), nematicity and superconductivity in $A$V$_{3}$Sb$_{5}$ ($A = {\rm K}$, Rb, Cs) compounds gives rise to a rich landscape of intriguing physical phenomena. In addition to the 2$a_{0}\times2a_{0}$ CDW, a unidirectional 4$a_{0}$ stripe CDW is also observed on the Sb surface of RbV$_{3}$Sb$_{5}$ and CsV$_{3}$Sb$_{5}$. However, reports of stripe-like CDWs in KV$_{3}$Sb$_{5}$ have been limited. Here, we report the first observation of a long-range unidirectional stripe order with a $6a_{0}$ modulation period on the Sb surface of KV$_{3}$Sb$_{5}$, coexisting with the $2a_{0} \times 2a_{0}$ CDW. Notably, the intensity of the $6a_{0}$ stripes in STM topographies exhibits pronounced contrast reversal between opposite bias voltages. Additionally, the wave vector of the $6a_{0}$ modulation shows no energy-dependent dispersion, confirming its CDW origin. Furthermore, the $6a_{0}$ CDW is robust under a 7 T out-of-plane magnetic field and persists over a temperature range from 215 mK to 720 mK. These results provide compelling evidence for the emergence of a long-range unidirectional CDW in KV$_{3}$Sb$_{5}$. Select Nontrivial Fermi surface topology in kagome superconductor CsTi3Bi5 revealed by de Haas-van Alphen oscillation Yuhang Zhang(张宇航), Xinwei Yi(易鑫伟), Zhen Zhao(赵振), Jiali Liu(刘家利), Aini Xu(胥艾妮), Dong Li(李栋), Zouyouwei Lu(鲁邹有为), Yue Liu(刘樾), Jihu Lu(卢佶虎), Hua Zhang(张华), Hui Chen(陈辉), Shiliang Li(李世亮), Ziyi Liu(刘子儀), Jinguang Cheng(程金光), Gang Su(苏刚), Haitao Yang(杨海涛), Xiaoli Dong(董晓莉), Hong-Jun Gao(高鸿钧), and Zhongxian Zhao(赵忠贤) Chin. Phys. B, 2025, 34 (7): 077107.   DOI: 10.1088/1674-1056/adc7f0 Abstract （210）   HTML （0）    PDF （1594KB）（180）       Knowledge map    The kagome lattice, naturally encompassing Dirac fermions, flat bands, and van Hove singularities, tends to intertwine exotic electronic states. Revealing the characteristics of its Fermi surface will help clarify the nature of the complex quantum phenomena in kagome material. Here we report the Fermi surface properties of the novel kagome metal CsTi$_{{3}}$Bi$_{{5}}$ by the de Haas-van Alphen oscillations. The observed oscillations are clear and consist of six principal frequencies ranging from 214 T to 1013 T. The angular dependence of the frequency implies a quasi-two-dimensional electronic structure. In addition, the geometry phase corresponding to 281 T, determined by direct Lifshitz-Kosevich formula fitting, yields a value close to $\pi $, which may indicate a band structure with nontrivial topological property. These results underscore the potential of CsTi$_{{3}}$Bi$_{{5}}$ as a promising platform to explore the interplay between topological order, electronic nematicity, and superconductivity. Select High-throughput discovery of kagome materials in transition metal oxide monolayers Renhong Wang(王人宏), Cong Wang(王聪), Ruixuan Li(李睿宣), Deping Guo(郭的坪), Jiaqi Dai(戴佳琦), Canbo Zong(宗灿波), Weihan Zhang(张伟涵), and Wei Ji(季威) Chin. Phys. B, 2025, 34 (4): 046801.   DOI: 10.1088/1674-1056/adb265 Abstract （291）   HTML （0）    PDF （1150KB）（235）       Knowledge map    Kagome materials are known for hosting exotic quantum states, including quantum spin liquids, charge density waves, and unconventional superconductivity. The search for kagome monolayers is driven by their ability to exhibit neat and well-defined kagome bands near the Fermi level, which are more easily realized in the absence of interlayer interactions. However, this absence also destabilizes the monolayer forms of many bulk kagome materials, posing significant challenges to their discovery. In this work, we propose a strategy to address this challenge by utilizing oxygen vacancies in transition metal oxides within a "1$+$3" design framework. Through high-throughput computational screening of 349 candidate materials, we identified 12 thermodynamically stable kagome monolayers with diverse electronic and magnetic properties. These materials were classified into three categories based on their lattice geometry, symmetry, band gaps, and magnetic configurations. Detailed analysis of three representative monolayers revealed kagome band features near their Fermi levels, with orbital contributions varying between oxygen 2p and transition metal d states. This study demonstrates the feasibility of the "1$+$3" strategy, offering a promising approach to uncovering low-dimensional kagome materials and advancing the exploration of their quantum phenomena. Select Scanning tunneling microscopy study on symmetry breaking of charge density wave in FeGe Jiakang Zhang(张嘉康), Ziyuan Chen(陈子元), Xueliang Wu(吴学良), Mingzhe Li(李明哲), Yuanji Li(李元骥), Ruotong Yin(尹若彤), Jiashuo Gong(巩佳硕), Shiyuan Wang(王适源), Aifeng Wang(王爱峰), Dong-Lai Feng(封东来), and Ya-Jun Yan(闫亚军) Chin. Phys. B, 2025, 34 (4): 047303.   DOI: 10.1088/1674-1056/adb389 Abstract （256）   HTML （0）    PDF （4756KB）（112）       Knowledge map    The complex symmetry breaking states in $A$V$_{3}$Sb$_{5}$ family have attracted extreme research attention, but controversy still exists, especially in the question of time reversal symmetry breaking of the charge density wave (CDW). Most recently, a chiral CDW has been suggested in kagome magnet FeGe, but the related study is very rare. Here, we use a scanning tunneling microscope to study the symmetry breaking behavior of both the short- and long-range CDWs in FeGe. Different from previous studies, our study reveals an isotropic long-range CDW without obvious symmetry breaking, while local rotational symmetry breaking appears in the short-range CDW, which may be related to the existence of strong structural disorders. Moreover, the charge distribution of the short-range CDW is inert to the applied external magnetic fields and the detailed spin arrangements of FeGe, inconsistent with the expectation of a chiral CDW associated with chiral flux. Our results rule out the existence of spontaneous chiral and rotational symmetry breaking in the CDW state of FeGe, putting strong constraints on the further understanding of CDW mechanism. Select Emergent 3×3 charge order on the Cs reconstruction of kagome superconductor CsV3Sb5 Xianghe Han(韩相和), Zhongyi Cao(曹钟一), Zihao Huang(黄子豪), Zhen Zhao(赵振), Haitao Yang(杨海涛), Hui Chen(陈辉), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2025, 34 (1): 016801.   DOI: 10.1088/1674-1056/ad8fa1 Abstract （400）   HTML （2）    PDF （1079KB）（131）       Knowledge map    The alkali adatoms with controlled coverage on the surface have been demonstrated to effectively tune the surface band of quantum materials through in situ electron doping. However, the interplay of orderly arranged alkali adatoms with the surface states of quantum materials remains unexplored. Here, by using low-temperature scanning tunneling microscopy/spectroscopy (STM/S), we observed the emergent 3$\times$3 super modulation of electronic states on the $\sqrt 3\times\sqrt 3R30^\circ$ (R3) Cs ordered surface of kagome superconductor CsV$_{3}$Sb$_{5}$. The nondispersive 3$\times$3 superlattice at R3 ordered surface shows contrast inversion in positive and negative differential conductance maps, indicating a charge order origin. The 3$\times$3 charge order is suppressed with increasing temperature and undetectable at a critical temperature of $\sim 62$ K. Furthermore, in the Ta substituted sample CsV$_{2.6}$Ta$_{0.4}$Sb$_{5}$, where long-range 2$\times$2$\times$2 charge density wave is significantly suppressed, the 3$\times$3 charge order on the R3 ordered surface becomes blurred and much weaker than that in the undoped sample. It indicates that the 3$\times$3 charge order on the R3 ordered surface is directly correlated to the bulk charge density waves in CsV$_{3}$Sb$_{5}$. Our work provides a new platform for understanding and manipulating the cascade of charge orders in kagome superconductors. Select Magnetoresistance hysteresis in the superconducting state of kagome CsV3Sb5 Tian Le(乐天), Jinjin Liu(刘锦锦), Zhiwei Wang(王秩伟), and Xiao Lin(林效) Chin. Phys. B, 2024, 33 (10): 107402.   DOI: 10.1088/1674-1056/ad6423 Abstract （337）   HTML （2）    PDF （872KB）（286）       Knowledge map    The hysteresis of magnetoresistance observed in superconductors is of great interest due to its potential connection with unconventional superconductivity. In this study, we perform electrical transport measurements on kagome superconductor CsV$_3$Sb$_5$ nanoflakes and uncover unusual hysteretic behavior of magnetoresistance in the superconducting state. This hysteresis can be induced by applying either a large DC or AC current at temperatures ($T$) well below the superconducting transition temperature ($T_{\rm c}$). As $T$ approaches $T_{\rm c}$, similar weak hysteresis is also detected by applying a small current. Various scenarios are discussed, with particular focus on the effects of vortex pinning and the presence of time-reversal-symmtery-breaking superconducting domains. Our findings support the latter, hinting at chiral superconductivity in kagome superconductors. Select Surface-sensitive electronic structure of kagome superconductor CsV3Sb5 Zhisheng Zhao(赵志生), Jianghao Yao(姚江浩), Rui Xu(徐瑞), Yuzhe Wang(王禹喆), Sen Liao(廖森), Zhengtai Liu(刘正太), Dawei Shen (沈大伟), Shengtao Cui(崔胜涛), Zhe Sun(孙喆), Yilin Wang(王义林), Donglai Feng(封东来), and Juan Jiang(姜娟) Chin. Phys. B, 2024, 33 (10): 107403.   DOI: 10.1088/1674-1056/ad7016 Abstract （288）   HTML （2）    PDF （2224KB）（152）       Knowledge map    We systematically study the electronic structure of a kagome superconductor ${\rm Cs}{\rm V}_{{\rm 3}}{{\rm Sb}}_{{\rm 5}}$ at different temperatures covering both its charge density wave state and normal state with angle-resolved photoemission spectroscopy. We observe that the V-shaped band around $\bar{\varGamma }$ shows three different behaviors, referred to as $\alpha /\alpha '$, $\beta $ and $\gamma $, mainly at different temperatures. Detailed investigations confirm that these bands are all from the same bulk Sb-p$_{z}$ origin, but they are quite sensitive to the sample surface conditions mainly modulated by temperature. Thus, the intriguing temperature dependent electronic behavior of the band near $\bar{\varGamma }$ is affected by the sample surface condition, rather than intrinsic electronic behavior originating from the phase transition. Our result systematically reveals the confusing electronic structure behavior of the energy bands around $\bar{\varGamma }$, facilitating further exploration of the novel properties in this material. Select Pairing correlation of the kagome-lattice Hubbard model with the nearest-neighbor interaction Chen Yang(杨晨), Chao Chen(陈超), Runyu Ma(马润宇), Ying Liang(梁颖), and Tianxing Ma(马天星) Chin. Phys. B, 2024, 33 (10): 107404.   DOI: 10.1088/1674-1056/ad7578 Abstract （304）   HTML （7）    PDF （927KB）（465）       Knowledge map    A recently discovered family of kagome lattice materials, ${A}\mathrm{V}_{3}\mathrm{Sb}_{5}$ (${A}=\mathrm{K,Rb,Cs}$), has attracted great interest, especially in the debate over their dominant superconducting pairing symmetry. To explore this issue, we study the superconducting pairing behavior within the kagome-lattice Hubbard model through the constrained path Monte Carlo method. It is found that doping around the Dirac point generates a dominant next-nearest-neighbor-d pairing symmetry driven by on-site Coulomb interaction $U$. However, when considering the nearest-neighbor interaction $V$, it may induce nearest-neighbor-p pairing to become the preferred pairing symmetry. Our results provide useful information to identify the dominant superconducting pairing symmetry in the ${A}\mathrm{V}_{3}\mathrm{Sb}_{5}$ family. Select Anomalous Hall effect and electronic correlation in a spin-reoriented kagome antiferromagnet LuFe6Sn6 Meng Lyu(吕孟), Yang Liu(刘洋), Shen Zhang(张伸), Junyan Liu(刘俊艳), Jinying Yang(杨金颖), Yibo Wang(王一博), Yiting Feng(冯乙婷), Xuebin Dong(董学斌), Binbin Wang(王彬彬), Hongxiang Wei(魏红祥), and Enke Liu(刘恩克) Chin. Phys. B, 2024, 33 (10): 107507.   DOI: 10.1088/1674-1056/ad6f93 Abstract （314）   HTML （2）    PDF （1289KB）（280）       Knowledge map    The kagome lattice system has been identified as a fertile ground for the emergence of a number of new quantum states, including superconductivity, quantum spin liquids, and topological electronic states. This has attracted significant interest within the field of condensed matter physics. Here, we present the observation of an anomalous Hall effect in an iron-based kagome antiferromagnet LuFe$_{6}$Sn$_{6}$, which implies a non-zero Berry curvature in this compound. By means of extensive magnetic measurements, a high Neel temperature, $T_{\rm N} = 552 $ K, and a spin reorientation behavior were identified and a simple temperature-field phase diagram was constructed. Furthermore, this compound was found to exhibit a large Sommerfeld coefficient of $\gamma = 87 $ mJ$\cdot $mol$^{-1}\cdot$K$^{-2}$, suggesting the presence of a strong electronic correlation effect. Our research indicates that LuFe$_{6}$Sn$_{6}$ is an intriguing compound that may exhibit magnetism, strong correlation, and topological states.