Observation of electronic nematicity driven by three-dimensional charge density wave in kagome lattice KV$_3$Sb$_5$

TL;DR

This study provides direct evidence of electronic nematicity driven by a three-dimensional charge density wave in KV$_3$Sb$_5$, revealing symmetry breaking and unidirectional electronic structures in kagome lattice superconductors.

Contribution

It presents the first direct reciprocal space evidence of rotation symmetry breaking in the CDW state of KV$_3$Sb$_5$, linking 3D charge order to electronic nematicity.

Findings

Unconventional unidirectionality indicating symmetry breaking from six-fold to two-fold.

Interlayer coupling with $ ext{pi}$-phase offset causes preferred two-fold symmetry.

Observation of back-folded bands related to charge order and superconductivity.

Abstract

Kagome superconductors AV$_3$Sb$_5$ (A = K, Rb, Cs) provide a fertile playground for studying intriguing phenomena, including non-trivial band topology, superconductivity, giant anomalous Hall effect and charge density wave (CDW). Recently, a $C_2$ symmetric nematic phase prior to the superconducting state in AV$_3$Sb$_5$ drew enormous attention due to its potential inheritance of the symmetry of the unusual superconductivity. However, direct evidence on the rotation symmetry breaking of the electronic structure in the CDW state from the reciprocal space is still rare, and the underlying mechanism remains ambiguous. The observation shows unconventional unidirectionality, indicative of rotation symmetry breaking from six-fold to two-fold. The interlayer coupling between adjacent planes with $\pi$-phase offset in the 2$\times$2$\times$2 CDW phase leads to the preferred two-fold symmetric electronic structure. These rarely observed unidirectional back-folded bands in KV$_3$Sb$_5$ may provide important insights into its peculiar charge order and superconductivity.