Phase-separated charge order and twinning across length scales in CsV3Sb5

We present x-ray scattering studies resolving structural twinning and phase separation in the charge density wave (CDW) state of the kagome superconductor ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$. The three-dimensional CDW state in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ 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. To resolve the impact of this metastability, we present reciprocal space mapping and real-space images of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ 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 ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ where rotational symmetry is broken by the three-dimensional charge density wave order but locally preserved for any single kagome layer.