Interlayer Hopping between Surface Mott Insulator and Bulk Band Insulator in layered 1T-TaS_{2}

TL;DR

This study investigates the interplay between Mott and band insulating states in layered 1T-TaS2 using surface-sensitive and bulk-sensitive spectroscopic techniques, revealing how interlayer hopping influences their evolution with temperature.

Contribution

It introduces a dual spectroscopic approach combined with DMFT calculations to distinguish and analyze coexisting insulating states in layered 1T-TaS2.

Findings

Identification of surface and bulk spectral features of Mott and band insulators.

Observation of temperature-induced softening and broadening of Hubbard excitations.

Evidence that interlayer hopping modulates the insulating states with temperature.

Abstract

In condensed matter physics, various mechanisms give rise to distinct insulating phases. The competition and interplay between these phases remain elusive, even for the seemingly most distinguishable band and Mott insulators. In multilayer systems, such interplay is mediated by interlayer hopping, which competes with the Coulomb repulsion to determine the nature of insulators. The layered compound 1T-TaS_{2} provides an ideal platform for investigating this phenomenon, as it naturally hosts coexisting Mott and band insulating states. However, distinguishing these distinct insulating states and characterizing the evolution remain challenging. In this study, we employ a dual approach utilizing surface-sensitive High-Resolution Electron Energy Loss Spectroscopy (HREELS) and bulk-sensitive Fourier-transform Infrared Spectroscopy (FTIR) to investigate the electronic excitation spectrum of 1T-TaS_{2}. Our methodology effectively identifies the features originating from the Mott and band insulators by analyzing the differences in their bulk and surface spectral weights, along with their energy distinctions. Based on the previous identification, we further investigate the evolution of insulating state features in the homostructure as they are modulated by temperature. The measurements and Dynamical Mean-Field Theory (DMFT) calculations suggest that the softening and broadening of Hubbard excitations in the Mott state with increasing temperature result from enhanced interlayer hopping between the Mott and band insulators.