Spectroscopic Evidence for a Three-Dimensional Charge Density Wave in Kagome Superconductor CsV$_3$Sb$_5$

TL;DR

This study uses ARPES to reveal a three-dimensional charge density wave in CsV3Sb5, demonstrating a quadrupling of the unit cell and providing insights into its complex electronic structure and relation to superconductivity.

Contribution

First direct electronic structure evidence of a 3D CDW in CsV3Sb5, showing a quadrupling of the unit cell and distinct distortions in kagome layers.

Findings

Evidence for a 3D CDW order with quadrupled unit cell.

Identification of a surface state related to the Cs-terminated surface.

Insights into the relationship between CDW and superconductivity.

Abstract

The recently discovered AV3Sb5 (A=K, Rb, Cs) family, possessing V kagome nets, has received considerable attention due to the topological electronic structure and intriguing correlated phenomena, including an exotic charge density wave (CDW) and superconductivity. Detailed electronic structure studies are essential to unravel the characteristics and origin of the CDW as well as its interplay with superconductivity. Here, we present angle-resolved photoemission spectroscopy (ARPES) measurements for CsV3Sb5 at multiple temperatures and photon energies to reveal the nature of the CDW from an electronic structure perspective. We present evidence for a three-dimensional (3D) CDW order. In the process we also pinpoint a surface state attributed to a Cs terminated surface. This state was previously attributed to band folding band due to a CDW along the c direction or a quantum well state from quantum confinement. The CDW expected 2-fold lattice reconstruction along c axis is observed to be a quadrupling of the unit cell, thus for the first time directly demonstrating the 3D nature of the CDW from the electronic structure perspective. Moreover, this 3D CDW configuration originates from two distinct types of distortions in adjacent kagome layers. These present results not only provide key insights into the nature of the unconventional CDW in CsV3Sb5 but also provides an important reference for further studies on the relationship between the CDW and superconductivity.