Interplay of electron-electron and electron-phonon interactions in the low temperature phase of 1T-TaS2

TL;DR

This study explores how electron-electron and electron-phonon interactions influence the electronic structure of 1T-TaS2, revealing the coexistence of charge-density-wave order and Mott gap, with implications for understanding disorder-induced phases.

Contribution

It provides direct experimental evidence of Mott gap renormalization due to electron-phonon coupling in 1T-TaS2 using high-resolution STM/STS measurements.

Findings

Charge-density-wave gap: 0.20-0.24 eV

Mott gap: 0.32 eV

Local Mott gap reduction at defect sites

Abstract

We investigate the interplay of the electron-electron and electron-phonon interactions in the electronic structure of an exotic insulating state in the layered dichalcogenide 1T-TaS2, where the charge-density-wave (CDW) order coexists with a Mott correlation gap. Scanning tunneling microscopy and spectroscopy measurements with high spatial and energy resolution determine unambiguously the CDW and the Mott gap as 0.20-0.24 eV and 0.32 eV, respectively, through the real space electron phases measured across the multiply formed energy gaps. An unusual local reduction of the Mott gap is observed on the defect site, which indicates the renormalization of the on-site Coulomb interaction by the electron-phonon coupling as predicted by the Hubbard-Holstein model. The Mott-gap renormalization provides new insight into the disorder-induced quasi-metallic phases of 1T-TaS2.