Dirac Nodal Lines and Nodal Loops in a Topological Kagome Superconductor CsV$_3$Sb$_5$

TL;DR

This study identifies CsV$_3$Sb$_5$ as a Dirac nodal line semimetal with multiple nodal lines and loops near the Fermi level, linking these topological features to its giant anomalous Hall conductivity.

Contribution

The paper provides the first identification of Dirac nodal lines and loops in CsV$_3$Sb$_5$, clarifying its band topology and highlighting the role of nodal loops in its transport properties.

Findings

Multiple Dirac nodal lines and loops are near the Fermi level.

Nodal loops are located at the Fermi level within experimental resolution.

Topological nodal loops may be responsible for the giant anomalous Hall conductivity.

Abstract

The intertwining of charge order, superconductivity and band topology has promoted the AV$_3$Sb$_5$ (A=K, Rb, Cs) family of materials to the center of attention in condensed matter physics. Underlying those mysterious macroscopic properties such as giant anomalous Hall conductivity (AHC) and chiral charge density wave is their nontrivial band topology. While there have been numerous experimental and theoretical works investigating the nontrivial band structure and especially the van Hove singularities, the exact topological phase of this family remains to be clarified. In this work, we identify CsV$_3$Sb$_5$ as a Dirac nodal line semimetal based on the observation of multiple Dirac nodal lines and loops close to the Fermi level. Combining photoemission spectroscopy and density functional theory, we identify two groups of Dirac nodal lines along $k_z$ direction and one group of Dirac nodal loops in the A-H-L plane. These nodal loops are located at the Fermi level within the instrumental resolution limit. Importantly, our first-principle analyses indicate that these nodal loops may be a crucial source of the mysterious giant AHC observed. Our results not only provide a clear picture to categorize the band structure topology of this family of materials, but also suggest the dominant role of topological nodal loops in shaping their transport behavior.