Institute for Solid States Physics, The University of Tokyo, Kashiwa, Japan.
Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing, China.
Nature. 2023 May;617(7961):488-492. doi: 10.1038/s41586-023-05907-x. Epub 2023 Apr 26.
The newly discovered kagome superconductors represent a promising platform for investigating the interplay between band topology, electronic order and lattice geometry. Despite extensive research efforts on this system, the nature of the superconducting ground state remains elusive. In particular, consensus on the electron pairing symmetry has not been achieved so far, in part owing to the lack of a momentum-resolved measurement of the superconducting gap structure. Here we report the direct observation of a nodeless, nearly isotropic and orbital-independent superconducting gap in the momentum space of two exemplary CsVSb-derived kagome superconductors-Cs(VNb)Sb and Cs(VTa)Sb-using ultrahigh-resolution and low-temperature angle-resolved photoemission spectroscopy. Remarkably, such a gap structure is robust to the appearance or absence of charge order in the normal state, tuned by isovalent Nb/Ta substitutions of V. Our comprehensive characterizations of the superconducting gap provide indispensable information on the electron pairing symmetry of kagome superconductors, and advance our understanding of the superconductivity and intertwined electronic orders in quantum materials.
新发现的 kagome 超导体为研究能带拓扑、电子有序和晶格几何之间的相互作用提供了一个很有前景的平台。尽管人们对该体系进行了广泛的研究，但超导基态的性质仍然难以捉摸。特别是，到目前为止，还没有就电子配对对称性达成共识，部分原因是缺乏对超导能隙结构的动量分辨测量。在这里，我们使用超高分辨率和低温角分辨光发射光谱，直接观察到两个典型的 CsVSb 衍生的 kagome 超导体 Cs(VNb)Sb 和 Cs(VTa)Sb 中在动量空间中不存在节点、近乎各向同性且与轨道无关的超导能隙。值得注意的是，这种能隙结构对正常态中电荷有序的出现或不存在具有鲁棒性，可通过 V 的等电子 Nb/Ta 取代来调节。我们对超导能隙的综合特征分析为 kagome 超导体的电子配对对称性提供了不可或缺的信息，并推进了我们对量子材料中超导性和交织电子有序的理解。
