Real-Space Investigation of the Charge Density Wave in VTe2 Monolayer with Rotational and Mirror Symmetries Broken

TL;DR

This study uses LEED and STM to investigate the (4x4) charge density wave in VTe2 monolayer, revealing real-space symmetry breaking and a CDW gap, suggesting a mechanism beyond conventional theories.

Contribution

First real-space observation of symmetry breaking in the CDW state of VTe2 monolayer using STM and LEED techniques.

Findings

(4x4) CDW transition at 192 K confirmed by LEED

Real-space 1D modulation breaks rotational and mirror symmetries

CDW gap of 12 meV detected at 4.9 K

Abstract

Recently the charge density wave (CDW) in vanadium dichalcogenides have attracted increasing research interests, but a real-space investigation on the symmetry breaking of the CDW state in VTe2 monolayer is still lacking. We have investigated the CDW of VTe2 monolayer by low energy electron diffraction (LEED) and scanning tunneling microscope (STM). While the LEED experiments revealed a (4X4) CDW transition at 192+-2 K, our low-temperature STM experiments resolved the (4X4) lattice distortions and charge-density modulation in real space, and further unveiled a 1D modulation that breaks the three-fold rotational and mirror symmetries in the CDW state. In accordance with the CDW state at low temperature, a CDW gap of 12 meV was detected by scanning tunneling spectroscopy (STS) at 4.9 K. Our work provides real-space evidence on the symmetry breaking of the (4X4) CDW state in VTe2 monolayer, and implies there is a certain mechanism, beyond the conventional Fermi surface nesting or the q-dependent electron-phonon coupling, is responsible for the formation of CDW state in VTe2 monolayer.