纳米标准与检测重点实验室第273期学术报告

报告题目：Understanding and Modulating a New Unconventional Kagome Superconductor

报 告 人：杨海涛 研究员 中科院物理所

时  间：2021年11月3日 上午9:30

地  点：国家纳米科学中心 科研楼三层阶梯教室

邀 请 人：裘晓辉 研究员

报告内容：𝐴V₃Sb₅ (𝐴 = K, Rb, Cs) is a newly discovered Kagome family that attracts great interest due to its topological nontrivial band structure and the coexistence of superconductivity (SC) and charge-density-wave (CDW) with exotic properties including a giant anomalous Hall effect. All these properties make AV₃Sb₅ an ideal system to study the interplay among the superconductivity, topological nontrivial band structure, and other rich phenomena within the Kagome lattice. Here, we report the preparation of the high-quality CsV₃Sb₅ single crystal with a SC transition temperature ∼ 3.5 K and Ti-doping CsV_3-xTi_xSb₅ single crystals with the modulating SC and CDW. Based on the electronical transport, magnetization, ARPES and μSR characterization, we find that a two-fold anisotropy of in-plane angular-dependent magnetoresistance in the mixed state and the CDW gap is strongly momentum dependent. We also observe strong TRSB signals below 70 K in CsV₃Sb₅ and conclude that the interlayer coupled chiral flux phase (CFP) is the most promising candidate for the TRSB state. Moreover, we observe a dome-shape SC diagram separated by the two distinct SC phase in the Ti-doping CsV_3-xTi_xSb₅ single crystals. These finding provide new insights into the mechanism of unconventional SC and multiple orders in Kagome systems.

个人简介：杨海涛，中科院物理所研究员，博士生导师。2004年博士毕业于中国科学院物理研究所，2004-2008年先后担任日本东北大学作21世纪卓越中心计划（COE）和日本学术振兴会（JSPS）博士后。2009年加入中科院物理所，期间（2016年）赴美国布朗大学孙守恒研究组访问研究。主要研究方向为低维材料的制备和性能研究。通过化学气相沉积和输运（CVD、CVT）方法制备具有层状结构的单晶和低维材料，结合极低温-强磁场扫描隧道显微镜和电输运、磁性、光学性能等表征手段研究超导、拓扑、强关联电子等物理性能。已在Nature，Nature Commun.，Adv. Energy Mater.和Nano Lett.等杂志发表文章80余篇。

报告题目：Roton pair density wave in a strong-coupling kagome superconductor

报 告 人：陈辉 副研究员 中科院物理所

时  间：2021年11月3日 上午9:30

地  点：国家纳米科学中心 科研楼三层阶梯教室

邀 请 人：裘晓辉 研究员

报告内容：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 (2∆/k_BT_c~5) that coexists with 4a₀ unidirectional and 2a₀×2a₀ 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-T_c cuprate superconductors, and provide groundwork for understanding the microscopic origin of correlated electronic states and superconductivity in vanadium-based kagome metals.

简介：陈辉，中科院物理所副研究员，博士生导师。 2017年博士毕业于中国科学院物理研究所，期间在美国内布拉斯加州州立大学林肯学校交流学习。随后继续在中科院物理所从事博士后研究，并出站留所工作，担任副研究员。 陈辉博士的主要研究方向是通过扫描隧道显微镜等表征、原位操纵、原位调控手段与多种精确制备技术相结合，原子级精准地构筑石墨烯“折纸”纳米结构、三分之一氢化石墨烯、单分子器件等新型纳米低维结构，并研究超导配对密度波，马约拉纳零能模、极化子等新奇物性。近几年取得了一系列突破性成果，作为第一与共同第一作者在Science，Nature，Nat. Phys.，Nat. Commun.，Adv. Mater. 和Nano Lett. 等杂志发表文章10余篇。2020年获国家基金委优青项目资助。