Phase-Separated Charge Order and Twinning Across Length Scales in CsV$_3$Sb$_5$

TL;DR

This study uses advanced X-ray techniques to reveal complex microstructures, phase segregation, and twinning in the charge density wave state of CsV$_3$Sb$_5$, highlighting metastability and local symmetry preservation.

Contribution

It provides the first detailed real-space and reciprocal-space analysis of microstructure, phase separation, and twinning in the CDW state of CsV$_3$Sb$_5$, emphasizing metastability and local symmetry.

Findings

Metastability in CDW supercell formation depends on thermal history and deformation.

Real-space phase segregation of different CDW supercells was directly observed.

Structural twinning driven by broken rotational symmetry was resolved.

Abstract

We present X-ray scattering studies resolving structural twinning and phase separation in the charge density wave (CDW) state of the kagome superconductor CsV$_3$Sb$_5$. The three-dimensional CDW state in CsV$_3$Sb$_5$ is reported to form a complex superposition of Star of David (SoD) or Tri-Hexagonal (TrH) patterns of distortion within its kagome planes, but the out-of-plane stacking is marked by metastability. In order to resolve the impact of this metastability, we present reciprocal space mapping and real-space images of CsV$_3$Sb$_5$ collected across multiple length scales using temperature-dependent high-dynamic range mapping (HDRM) and dark-field X-ray microscopy (DFXM). The experimental data provide evidence for a rich microstructure that forms in the CDW state. Data evidence metastability in the formation of $2\times 2\times 4$ and $2\times 2\times 2$ CDW supercells dependent on thermal history and mechanical deformation. We further directly resolve the real space phase segregation of both supercells as well as a real-space, structural twinning driven by the broken rotational symmetry of the CDW state. Our combined results provide insights into the role of microstructure and twinning in experiments probing the electronic properties of CsV$_3$Sb$_5$ where rotational symmetry is broken by the three-dimensional charge density wave order but locally preserved for any single kagome layer.