Mott versus hybridization gap in the low-temperature phase of $1T$-TaS$_2$

TL;DR

This study uses advanced computational methods to analyze the electronic structure of $1T$-TaS$_2$ bilayers, revealing how surface termination influences insulating and metallic states, and aligning with experimental observations.

Contribution

It applies the $GW$ + EDMFT method to $1T$-TaS$_2$ bilayers, providing new insights into the effects of surface termination and correlation-induced gaps.

Findings

Surface termination determines insulating or metallic surface states.

A Mott gap forms in the surface state, smaller than the bilayer gap.

Experimental data shows coexistence of regions with different electronic gaps.

Abstract

We compute the correlated electronic structure of stacked $1T$-TaS$_2$ bilayers using the $GW$ + EDMFT method. Depending on the surface termination, the semi-infinite uncorrelated system is either band-insulating or exhibits a metallic surface state. For realistic values of the onsite and intersite interactions, a Mott gap opens in the surface state, but this gap is smaller than the gap originating from the bilayer structure. Our results are consistent with recent scanning tunneling spectroscopy measurements for different terminating layers, and with our own photoemission measurements, which indicate the coexistence of spatial regions with different gaps in the electronic spectrum.