Honeycomb-Lattice Mott insulator on Tantalum Disulphide

TL;DR

This paper demonstrates a novel method to create a strongly interacting 2D honeycomb lattice with topological properties using potassium adatoms on 1T-TaS2, revealing a Mott insulator with potential for exotic quantum states.

Contribution

It introduces an innovative approach to engineer a honeycomb lattice with strong electron interactions from a known triangular lattice Mott insulator.

Findings

Formation of a honeycomb lattice with narrow topological bands

Observation of a large charge gap indicating strong correlations

Potential realization of a Mott insulator with finite spin Chern number

Abstract

Effects of electron many-body interactions amplify in an electronic system with a narrow bandwidth opening a way to exotic physics. A narrow band in a two-dimensional (2D) honeycomb lattice is particularly intriguing as combined with Dirac bands and topological properties but the material realization of a strongly interacting honeycomb lattice described by the Kane-Mele-Hubbard model has not been identified. Here we report a novel approach to realize a 2D honeycomb-lattice narrow-band system with strongly interacting 5$d$ electrons. We engineer a well-known triangular lattice 2D Mott insulator 1T-TaS$_2$ into a honeycomb lattice utilizing an adsorbate superstructure. Potassium (K) adatoms at an optimum coverage deplete one-third of the unpaired $d$ electrons and the remaining electrons form a honeycomb lattice with a very small hopping. Ab initio calculations show extremely narrow Z$_2$ topological bands mimicking the Kane-Mele model. Electron spectroscopy detects an order of magnitude bigger charge gap confirming the substantial electron correlation as confirmed by dynamical mean field theory. It could be the first artificial Mott insulator with a finite spin Chern number.