Moir\'e quantum chemistry: charge transfer in transition metal dichalcogenide superlattices

TL;DR

This paper develops a theoretical framework combining first-principles calculations and continuum models to understand charge transfer phenomena in moiré superlattices of transition metal dichalcogenides, revealing new insulating states.

Contribution

It introduces a novel electronic structure theory that maps TMD heterobilayers onto diatomic crystals, explaining charge transfer and insulating states in moiré systems.

Findings

Charge transfer occurs between regions several nanometers apart.

The insulating state at half-filling is a charge-transfer insulator, not a Mott-Hubbard insulator.

The theory explains recent experimental observations in WSe₂/WS₂ bilayers.

Abstract

Transition metal dichalcogenide (TMD) bilayers have recently emerged as a robust and tunable moir\'e system for studying and designing correlated electron physics. In this work, by combining large-scale first principle calculation and continuum model approach, we provide an electronic structure theory that maps long-period heterobilayer TMD superlattices onto diatomic crystals with cations and anions. We find that the interplay between moir\'e potential and Coulomb interaction leads to filling-dependent charge transfer between MM and MX regions several nanometers apart. We show that the insulating state at half-filling found in recent experiments on WSe$_2$/WS$_2$ is a charge-transfer insulator rather than a Mott-Hubbard insulator. Our work reveals the richness of simplicity in moir\'e quantum chemistry.