Dynamics of electronic states in the insulating Intermediate surface phase of 1T-TaS$_2$

TL;DR

This study investigates the electronic and collective dynamics of the intermediate insulating surface phase of 1T-TaS$_2$, revealing its unique persistence and properties compared to the bulk, using advanced spectroscopic techniques.

Contribution

It provides a comparative analysis of surface and bulk electronic states in 1T-TaS$_2$, highlighting the distinct behavior of the surface intermediate phase and its dynamical properties.

Findings

Surface exhibits a persistent intermediate insulating phase with weaker Coulomb screening.

Amplitude mode at the surface is stiffer and shows variable coupling to electronic states.

Surface phase remains insulating over a temperature range where bulk is metallic.

Abstract

This article reports a comparative study of bulk and surface properties in the transition metal dichalcogenide 1T-TaS$_2$. When heating the sample, the surface displays an intermediate insulating phase that persists for $\sim 10$ K on top of a metallic bulk. The weaker screening of Coulomb repulsion and stiffer Charge Density Wave (CDW) explain such resilience of a correlated insulator in the topmost layers. Both time resolved ARPES and transient reflectivity are employed to investigate the dynamics of electrons and CDW collective motion. It follows that the amplitude mode is always stiffer at the surface and displays variable coupling to the Mott-Peierls band, stronger in the low temperature phase and weaker in the intermediate one.