笼目超导体CsV3Sb5: 独特的电子结构

论文

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速递

Topological surface states and flat bands in the kagome superconductor CsV₃Sb₅

Yong Hu, Samuel M. L. Teicher, Brenden R. Ortiz, Yang Luo, Shuting Peng, Linwei Huai, Junzhang Ma, Nicholas C. Plumb, Stephen D. Wilson, Junfeng He, Ming Shi

Science Bulletin, 2022, 67(5): 495–500 

doi: 10.1016/j.scib.2021.11.026

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简介

具有多种电子序和丰富物态的量子材料中往往蕴含着奇异的量子现象. 不同电子序和量子态之间的相互作用也可以产生新的物理现象. 本研究揭示了笼目超导体CsV₃Sb₅的独特电子结构. 科研人员在费米能附近发现了拓扑非平庸的表面态, 这意味着拓扑物理很可能会参与到超导态中；同时还直接观测到了平带, 这表明电子关联作用会在笼目超导体CsV₃Sb₅中起着重要的作用. 这些结果表明笼目晶格CsV₃Sb₅不仅具有实现马约拉纳零模和奇异超导态的潜力, 还是一个独特的可用于探索电荷密度波有序、拓扑量子态、强关联效应和超导性之间的相互作用的研究平台. 

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图文速览

Fig. 1  Crystal structure and electronic structure of the kagome superconductors CsV₃Sb₅. (a) Exotic electronic orders in CsV₃Sb₅, including superconductivity, charge density wave (CDW) and topological states. (b) Tight-binding band structure of kagome lattice featuring a Dirac dispersion and a flat band. (c) Top view of the kagome plane (left) and the structural unitcell (right) of CsV₃Sb₅. (d) Schematic of the bulk and surface Brillouin zones along the (001) surface of CsV₃Sb₅. The high-symmetry points are marked. (e) 3D photo emission intensity plot measured with 90 eV photons. 

Fig. 2  Band structure above the CDW transition temperature. (a) Fermi surface map of CsV₃Sb₅. (b) Photon energy-dependent ARPES spectral intensity map at the E_F along the`K –`Γ –`K direction. (c), (d) Experimental (c) and calculated (d) band dispersion along the`Γ –`K –`M –`K direction. (e) Zoom-in plots of the calculated bands in a selected region (region 1) in (d), as indicated by the pink dashed box. (f), (g) Experimental bands in the same region, measured with circular right (CR) and LV polarization, respectively. The characteristic points (C1–C4) are marked with different markers. (h), (i) Same as (c, d), but along the`Γ –`M direction. (j) Second derivative image of the original data with respect to momentum, for the selected region (region 2) in (h), as indicated by the pink dashed box. (k) Calculated bands in the same region. The orange dashed curve in (j) is an eye-guide for the TSSs (Fig. S2 online). (l) Energy distribution curves (EDCs) around`M point of the`Γ –`M momentum cut. Orange circles mark the energy features of the TSSs. All measurements were performed at 200 K, and the Fermi-Dirac function is divided out to reveal the energy region slightly above the E_F.

Fig. 3  Band structure below the CDW transition temperature. (a), (b) Experimental band dispersion in the CDW phase along the`Γ–`K –`M –`K direction collected at 5.5 K, with the CR and LV polarizations, respectively. The red circles, stars, triangles, and squares indicate the characteristic points C1, C2,  C3, and C4, respectively. (c), (d) Same as (a, b), but measured at 200 K. (e), (f) Calculated bands along the`Γ –`K –`M –`K direction in the CDW phase with the Hex-Triangle structure and in the normal state (T>T_CDW), respectively. (g) Temperature evolution of the EDC at the Dirac-like crossing point C2, as indicated by the red line in (a). (h) Second derivative image with respect to momentum for the band structure along the`M –`Γ –`M direction taken at 5.5 K.

Fig. 4  Identification of flat bands in CsV₃Sb₅. (a), (b) Experimental band dispersion along the`Γ –`K –`M –`K and`M –`Γ –`M high symmetry directions, respectively. The orange box is an eye-guide for the nearly flat band. The bands are probed with circularly polarized light. (c) Calculated band structure along the`Γ –`K –`M –`K direction. Schematic of the locations of the momentum cuts is shown in the inset. (d) Symmetrized image of the band structure along the`M –`Γ –`M direction, probed with the LV polarized light. Experimental data were collected at 200 K.

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本文通讯作者

Stephen D. Wilson 教授  美国加利福尼亚大学圣芭芭拉分校材料系. 主要研究兴趣为强关联量子材料, 关注自旋轨道耦合材料中的新物态, 以及功能材料中的多体相互作用。

何俊峰  教授 中国科学技术大学物理系. 主要从事强关联量子材料的电子结构研究.

史  明  研究员  瑞士保罗谢尔联邦研究所. 主要从事新型量子材料和强关联系统中的电子行为.

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