Transport Evidence for Wigner Crystals in Monolayer MoTe2

TL;DR

This study provides transport evidence for Wigner crystal formation in monolayer MoTe2, revealing antiferromagnetic interactions, a metal-insulator transition, and non-equilibrium states, advancing understanding of strongly correlated 2D electronic systems.

Contribution

First demonstration of Wigner crystal formation in monolayer MoTe2 with detailed magnetic and transport properties, highlighting its potential for studying correlated electron phenomena.

Findings

Observation of a metal-insulator transition at high r_s values.

Thermal melting of Wigner crystals below 2 K.

Enhanced spin susceptibility with antiferromagnetic interactions.

Abstract

The crystallization of charge carriers, dubbed the Wigner crystal, is anticipated at low densities in clean two-dimensional electronic systems (2DES). While there has been extensive investigation across diverse platforms, probing spontaneous charge and spin ordering is hindered by disorder effects and limited interaction energies. Here, we report transport evidence for Wigner crystals with antiferromagnetic exchange interactions in high-quality, hexagonal boron nitride encapsulated monolayer MoTe2, a system that achieves a large interaction parameter (r_s) at proper hole densities. A density-tuned metal-insulator transition (MIT) occurring at 3.1E10^11 cm-2 (corresponding to r_s~32) and pronounced nonlinear charge transport in the insulating regime at low temperatures signify the formation of Wigner crystals. Thermal melting of the crystalline phase is observed below approximately 2 K via temperature-dependent nonlinear transport. Magnetoresistance measurements further reveal a substantial enhancement of spin susceptibility as approaching the MIT. The temperature dependence of spin susceptibility in the Wigner crystal phase closely follows the Curie-Weiss law, with the extracted negative Weiss constant illustrating antiferromagnetic exchange interactions. Furthermore, we have found the system exhibits metallic-like differential resistivity under finite DC bias, possibly indicating the existence of a non-equilibrium coherent state in the depinning of Wigner crystals. Our observations establish monolayer MoTe2 as a promising platform for exploring magnetic and dynamic properties of Wigner crystals.