The transition-metal kagome lattice materials host frustrated, correlated, and topological quantum states of matter. Recently, a new family of vanadium-based kagome metals AV3Sb5 (A=K, Rb, and Cs) with topological band structures has been discovered. These layered compounds are nonmagnetic and undergo charge density wave transitions before developing superconductivity at low temperatures. Here we report the observation of unconventional superconductivity and pair density wave (PDW) in CsV3Sb5 using scanning tunneling microscope/spectroscopy (STM/STS) and Josephson STS. We find that CsV3Sb5 exhibits a V-shaped pairing gap Δ~0.5 meV and is a strong-coupling superconductor (2Δ/kBTc~5) that coexists with 4a0 unidirectional and 2a0X2a0 charge order. Remarkably, we discover a 3Q PDW accompanied by bidirectional 4a0/3 spatial modulations of the superconducting gap, coherence peak and gap-depth in the tunneling conductance. We term this novel quantum state a roton-PDW associated with an underlying vortex-antivortex lattice that can account for the observed conductance modulations. Probing the electronic states in the vortex halo in an applied magnetic field, in strong-field that suppresses superconductivity, and in zero-field above Tc reveals that the PDW is a primary state responsible for an emergent pseudogap and intertwined electronic order. Our findings show striking analogies and distinctions to the phenomenology of high-Tc cuprate superconductors, and provide groundwork for understanding the microscopic origin of correlated electronic states and superconductivity in vanadium-based kagome metals.
Comment on "Unconventional Fermi Surface Instabilities in the Kagome Hubbard Model" by M. Kiesel, C. Platt, and R. Thomale, Phys. Rev. Lett. {\bf 110}, 126405 (2013)
Pressure-induced unconventional charge-density-wave states in kagome metal AV3Sb5 (A = K, Rb, Cs)
Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China（中国科学技术大学微观尺度物理国家研究中心）；Department of Physics, University of Science and Technology of China（中国科学技术大学物理系）；School of Physics, Hefei University of Technology（合肥工业大学物理学院）；Collaborative Innovation Center of Advanced Microstructures, Nanjing University（南京大学先进微结构协同创新中心）；Hefei National Laboratory, University of Science and Technology of China（中国科学技术大学合肥国家实验室）
Direct Evidence of Unconventional Superconductivity in Doped Kagome system RV$_3$Sb$_5$
University of Illinois at Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；University of California Santa Barbara（加州大学圣塔芭芭拉分校）
Unconventional superconductivity in ScIr$_2$ chiral crystal with a kagome lattice
East China Normal University（华东师范大学）；Key Laboratory of Polar Materials and Devices (MOE), East China Normal University（华东师范大学极化材料器件教育部重点实验室）；Tianjin University（天津大学）；Technical University Dortmund（多特蒙德工业大学）；Laboratorium für Festkörperphysik, ETH Zürich（苏黎世联邦理工学院固体物理实验室）
Resolving unconventional gap structure in kagome superconductors with hybrid microwave circuits
Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体和化学物理研究所）；Institute of Solid State and Material Physics, Technische Universität Dresden（德累斯顿工业大学固态与材料物理研究所）；Institute of Applied Physics, Technische Universität Dresden（德累斯顿工业大学应用物理研究所）；Leibniz Institute for Solid State and Materials Research Dresden（德累斯顿莱布尼茨固体与材料研究所）；Department of Physics, University of Naples Federico II（那不勒斯费德里科二世大学物理系）；Department of Electrical Engineering and Information Technology, University of Naples Federico II（那不勒斯费德里科二世大学电气与信息工程系）
Direct Observation of Channelised Supercurrents in a Kagome Superconductor
Huygens-Kamerlingh Onnes Laboratory, Leiden University（莱顿大学休厄斯-卡末林·昂纳斯实验室）；University of California Santa Barbara（加州大学圣塔芭芭拉分校）；QuantaMap B.V.（QuantaMap有限公司）；Delft University of Technology（代尔夫特理工大学）；University of Zürich（苏黎世大学）；Ludwig-Maximilians-University Munich（慕尼黑路德维希-马克西米利安大学）
Flat bands and distinct density wave orders in correlated Kagome superconductor CsCr$_3$Sb$_5$
University of Science and Technology of China（中国科学技术大学）；Fuzhou University（福州大学）；Beijing Institute of Technology（北京理工大学）；Shanghai Advanced Research Institute, Chinese Academy of Sciences（中国科学院上海高等研究院）；National Synchrotron Radiation Laboratory and School of Nuclear Science and Technology, University of Science and Technology of China（中国科学技术大学核科学与技术学院/国家同步辐射实验室）；SLAC National Accelerator Laboratory（斯坦福直线加速器中心）
A Strongly Anisotropic Superconducting Gap in the Kagome Superconductor CsV$_3$Sb$_5$: A Study of Directional Point-Contact Andreev Reflection Spectroscopy
Discovery of parity-violating chiral polar-nematic charge density wave and superconductivity in kagome metals
Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Hefei National Laboratory（合肥国家实验室）；Department of Physics, Boston College（波士顿学院物理系）；Department of Applied Physics, The Hong Kong Polytechnic University（香港理工大学应用物理系）；Department of Chemistry, National University of Singapore（新加坡国立大学化学系）
Novel dynamical excitations and roton-based measurement of Cooper-pair momentum in a two-dimensional Fulde-Ferrell-Larkin-Ovchinnikov superfluid on optical lattices
Key Laboratory for Microstructural Material Physics of Hebei Province, School of Science, Yanshan University（河北工业大学微观结构物理重点实验室，理学院，燕山大学）；Centre for Theoretical and Computational Physics, College of Physics, Qingdao University（青岛大学物理学院理论计算物理中心）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）
