Evidence for reduced periodic lattice distortion within the Sb-terminated surface layer of the kagome metal CsV$_3$Sb$_5$

TL;DR

This study uses low-energy electron diffraction to investigate the surface lattice distortion in CsV$_3$Sb$_5$, revealing that the surface distortion is less pronounced than in the bulk, challenging previous assumptions about the CDW structure.

Contribution

It provides direct experimental evidence that the periodic lattice distortion at the surface differs from the bulk in CsV$_3$Sb$_5$, using LEED with a focused electron beam.

Findings

No superstructure reflexes observed at the surface.

Surface lattice distortion is weaker than in the bulk.

Surface structure differs from bulk CDW predictions.

Abstract

The discovery of the kagome metal CsV$_3$Sb$_5$ sparked broad interest, due to the coexistence of a charge density wave (CDW) phase and possible unconventional superconductivity in the material. In this study, we use low-energy electron diffraction (LEED) with a $\mu$m-sized electron beam to explore the periodic lattice distortion at the antimony-terminated surface in the CDW phase. We recorded high-quality backscattering diffraction patterns in ultrahigh vacuum from multiple cleaved samples. Unexpectedly, we did not find superstructure reflexes at intensity levels predicted from dynamical LEED calculations for the reported $2 \times 2 \times 2$ bulk structure. Our results suggest that in CsV$_3$Sb$_5$ the periodic lattice distortion accompanying the CDW is less pronounced at Sb-terminated surfaces than in the bulk.