Spin-polarons and ferromagnetism in doped dilute Wigner-Mott insulators

TL;DR

This paper explores how doping in moiré heterostructures of transition metal dichalcogenides leads to spin-polaron formation, resulting in ferromagnetic order, with specific experimental signatures predicted.

Contribution

It introduces the concept that dilute doping induces ferromagnetism via spin-polarons in Wigner-Mott insulators, a novel mechanism in these materials.

Findings

Doped electrons form spin-polarons in the system.

Spin-polarons induce ferromagnetic order at relevant temperatures.

Explicit signatures of polaron formation are predicted in magnetization profiles.

Abstract

Moir\'e heterostructures of transition metal dichalcogenides exhibit Mott-insulating behaviour both at half-filling as well as at fractional fillings, where electronic degrees of freedom form self-organized Wigner crystal states. An open question concerns magnetic states obtained by lifting the pseudospin-1/2 degeneracy of these states at lowest temperatures. While at half-filling virtual hopping is expected to induce (weak) antiferromagnetic exchange interactions, these are strongly suppressed when considering $\textit{dilute}$ filling fractions. We argue that instead a small concentration of doped electrons leads to the formation of spin-polarons, inducing ferromagnetic order at experimentally relevant temperatures. We predict explicit signatures of polaron-formation in the magnetization profile of the system.