Abundance of correlated insulating states at fractional fillings of WSe$_{2}$/WS$_{2}$ moir\'e superlattices

TL;DR

This study reports the discovery of nearly twenty correlated insulating states at fractional fillings in WSe₂/WS₂ moiré heterostructures, enabled by a novel optical sensing technique sensitive to dielectric environment, revealing complex charge ordering phenomena.

Contribution

The paper introduces a new optical sensing method to detect correlated insulating states in moiré heterostructures and maps out a series of charge-ordered states at fractional fillings.

Findings

Nearly two-dozen correlated insulating states observed.

Energy ordering symmetric about half filling.

Proposed charge-ordered states include Wigner crystals and charge density waves.

Abstract

Quantum particles on a lattice with competing long-range interactions are ubiquitous in physics. Transition metal oxides, layered molecular crystals and trapped ion arrays are a few examples out of many. In the strongly interacting regime, these systems often exhibit a rich variety of quantum many-body ground states that challenge theory. The emergence of transition metal dichalcogenide moir\'e heterostructures provides a highly controllable platform to study long-range electronic correlations. Here we report an observation of nearly two-dozen correlated insulating states at fractional fillings of a WSe$_{2}$/WS$_{2}$ moir\'e heterostructure. The discovery is enabled by a new optical sensing technique that is built on the sensitivity to dielectric environment of the exciton excited states in single-layer semiconductor WSe$_{2}$. The cascade of insulating states exhibits an energy ordering which is nearly symmetric about filling factor of half electron (or hole) per superlattice site. We propose a series of charge-ordered states at commensurate filling fractions that range from generalized Wigner crystals to charge density waves. Our study lays the groundwork for utilizing moir\'e superlattices to simulate a wealth of quantum many-body problems that are described by the two-dimensional t-V model or spin models with long-range charge-charge and exchange interactions.