Distinguishing a Mott Insulator from a Trivial Insulator with Atomic Adsorbates

TL;DR

This paper presents a method to distinguish Mott insulators from trivial insulators by analyzing their chemical behavior with atomic adsorbates, using 1T-TaS2 as a case study, thereby clarifying its true ground state.

Contribution

It introduces a novel experimental approach to identify correlated insulators through surface chemistry, resolving debates about the nature of 1T-TaS2's insulating state.

Findings

Potassium adatoms behave differently on Mott vs. trivial insulator surfaces.

Spectral gap sizes vary on different surface terminations.

The behavior aligns with fundamental electronic orbital differences.

Abstract

In an electronic system with various interactions intertwined, revealing the origin of its many-body ground state is challenging and a direct experimental way to verify the correlated nature of an insulator has been lacking. Here we demonstrate a way to unambiguously distinguish a paradigmatic correlated insulator, a Mott insulator, from a trivial band insulator based on their distinct chemical behavior for a surface adsorbate using 1T-TaS2, which has been debated between a spin-frustrated Mott insulator or a spin-singlet trivial insulator. We start from the observation of different sizes of spectral gaps on different surface terminations and show that potassium adatoms on these two surface layers behave in totally different ways. This can be straightforwardly understood from distinct properties of a Mott and a band insulators due to the fundamental difference of a half and a full-filled orbital involved respectively. This work not only solves an outstanding problem in this particularly interesting material but also provides a simple touchstone to identify the correlated ground state of electrons experimentally.