Pervasive electronic nematicity as the parent state of kagome superconductors

TL;DR

This study reveals pervasive electronic nematicity in kagome superconductors, persisting beyond charge density wave phases, suggesting nematicity as the fundamental parent state underlying their exotic phenomena.

Contribution

It demonstrates that electronic nematicity exists independently of charge density waves in kagome superconductors, challenging previous assumptions about their relationship.

Findings

Nematicity persists after charge density wave suppression

Nematic regions are nanoscale and short-range

Electronic nematicity is intrinsic to the parent state

Abstract

Kagome superconductors $A$V$_3$Sb$_5$ ($A$ = Cs, K, Rb) have developed into an exciting playground for realizing and exploring exotic solid state phenomena. Abundant experimental evidence suggests that electronic structure breaks rotational symmetry of the lattice, but whether this may be a simple consequence of the symmetry of the underlying 2 $\times$ 2 charge density wave phase or an entirely different mechanism remains intensely debated. We use spectroscopic imaging scanning tunneling microscopy to explore the phase diagram of the prototypical kagome superconductor CsV$_3$Sb$_5$ as a function of doping. We intentionally suppress the charge density wave phase with chemical substitutions selectively introduced at two distinct lattice sites, and investigate the resulting system. We discover that rotational symmetry breaking of the electronic structure -- now present in short-range nanoscale regions -- persists in all samples, in a wide doping range long after all charge density waves have been suppressed. As such, our experiments uncover ubiquitous electronic nematicity across the $A$V$_3$Sb$_5$ phase diagram, unrelated to the 2 $\times$ 2 charge density wave. This further points towards electronic nematicity as the intrinsic nature of the parent state of kagome superconductors, under which other exotic low-temperature phenomena subsequently emerge.