Origin of charge density wave in the layered kagome metal CsV3Sb5

Abstract

Using first-principles calculations, we identify the origin of the observed charge density wave (CDW) formation in a layered kagome metal ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$. It is revealed that the structural distortion of kagome lattice forming the trimeric and hexameric V atoms is accompanied by the stabilization of quasimolecular states, which gives rise to the opening of CDW gaps for the V-derived multibands lying around the Fermi level. We, thus, propose the Jahn-Teller-like instability having the local lattice distortion and its derived quasimolecular states as a driving force of the CDW order. Specifically, the saddle points of multiple Dirac bands near the Fermi level, located at the $M$ point, are hybridized to disappear along the ${k}_{z}$ direction, therefore, not supporting the widely accepted Peierls-like electronic instability due to Fermi surface nesting. It is further demonstrated that applied hydrostatic pressure significantly reduces the interlayer spacing to destabilize the quasimolecular states, leading to a disappearance of the CDW phase at a pressure of $\ensuremath{\sim}2\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$. The presently proposed underlying mechanism of the CDW order in ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ can also be applicable to other isostructural kagome lattices, such as ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ and ${\mathrm{RbV}}_{3}{\mathrm{Sb}}_{5}$.