Role of electron-electron interactions in $M$-valley twisted transition metal dichalcogenides

TL;DR

This study explores how electron-electron interactions and interlayer bias influence the electronic properties and correlated phases in $M$-valley twisted transition metal dichalcogenides, revealing tunable Van Hove singularities and magnetic states.

Contribution

It demonstrates that interactions and bias significantly modify moiré band structures and phase diagrams, highlighting tunable correlated phenomena in $M$-valley 1T TMDs.

Findings

Interactions pin Van Hove singularities to the Fermi level.

Competition between ferromagnetic and antiferromagnetic states.

Band mixing effects depend on twist angle and stacking.

Abstract

We investigate the role of long-range Coulomb interactions in $M$-valley moir\'es using the self-consistent Hartree-Fock approximation. This platform was recently proposed [Nature 643, 376 (2025) and arXiv:2411.18828 (2024)] as a new class of experimentally realizable moir\'e materials using twisted transition metal dichalcogenides homobilayers with the 1T structure. While these seminal studies considered the noninteracting theory without an electric displacement field, this work shows that both electron-electron interactions at finite doping and an interlayer bias strongly modify the moir\'e bands. For small twists ($\lesssim 5^\circ$) the density of states versus filling and interlayer bias displays qualitatively different behavior for twisting near aligned ($0^\circ$) and antialigned ($60^\circ$) stacking with tunable Van Hove singularities (VHSs). Moreover, interactions pin the VHS to the Fermi energy over a finite range of doping both at zero and finite bias depending on the stacking type, an effect known to enhance both superconductivity and strongly correlated states. At half filling, we obtain the phase diagram as a function of interaction strength, interlayer bias, and twist angle. We find a competition driven by band mixing between an isotropic ferromagnet and an antiferromagnet that are nearly degenerate over a wide range of experimentally accessible parameters. Our work demonstrates that correlated states in $M$-valley 1T tTMDs can be strongly tuned in situ both by applying an electric displacement field and by electron doping.