Metal to Mott Insulator Transition in Two-dimensional 1T-TaSe$_2$

TL;DR

This study demonstrates a dimensionality-driven transition from metal to Mott insulator in 1T-TaSe2 as it is thinned to atomic layers, revealing new strongly correlated physics opportunities in 2D materials.

Contribution

It is the first to show that reducing thickness in 1T-TaSe2 induces a metal to Mott insulator transition, linking bulk metallicity to a 2D Mott insulating state.

Findings

Bulk 1T-TaSe2 is metallic due to a band crossing Fermi level.

Thinning down to atomic layers quenches electron kinetic energy.

The transition resolves the metallic bulk and insulating surface dichotomy.

Abstract

When electron-electron interaction dominates over other electronic energy scales, exotic, collective phenomena often emerge out of seemingly ordinary matter. The strongly correlated phenomena, such as quantum spin liquid and unconventional superconductivity, represent a major research frontier and a constant source of inspiration. Central to strongly correlated physics is the concept of Mott insulator, from which various other correlated phases derive. The advent of two-dimensional (2D) materials brings unprecedented opportunities to the study of strongly correlated physics in the 2D limit. In particular, the enhanced correlation and extreme tunability of 2D materials enables exploring strongly correlated systems across uncharted parameter space. Here, we discover an intriguing metal to Mott insulator transition in 1T-TaSe$_2$ as the material is thinned down to atomic thicknesses. Specifically, we discover, for the first time, that the bulk metallicity of 1T-TaSe$_2$ arises from a band crossing Fermi level. Reducing the dimensionality effectively quenches the kinetic energy of the initially itinerant electrons and drives the material into a Mott insulating state. The dimensionality-driven Metal to Mott insulator transition resolves the long-standing dichotomy between metallic bulk and insulating surface of 1T-TaSe$_2$. Our results additionally establish 1T-TaSe$_2$ as an ideal variable system for exploring various strongly correlated phenomena.