Relativistic Mott transition in strongly correlated artificial graphene

TL;DR

This paper demonstrates the realization of a strongly correlated artificial graphene system in twisted WSe2 tetralayers, observing a relativistic Mott transition characterized by Dirac fermion behavior and antiferromagnetic insulating states.

Contribution

It reports the first observation of a relativistic Mott transition in artificial graphene created from twisted WSe2, enabling study of strongly correlated Dirac fermions.

Findings

Observation of Dirac-like band structure in moiré valence band

Detection of a semimetal-insulator transition tuned by twist angle

Evidence of antiferromagnetic Mott insulating state

Abstract

The realization of graphene has provided a bench-top laboratory for quantum electrodynamics. The low-energy excitations of graphene are two-dimensional massless Dirac fermions with opposite chiralities at the $\pm$K valleys of the graphene Brillouin zone. It has been speculated that the electron-electron interactions in graphene could spontaneously break the chiral symmetry to induce a finite mass for Dirac fermions, in analogue to dynamical mass generation in elementary particles. The phenomenon is also known as the relativistic Mott transition and has not been observed in pristine graphene because the interaction strength is insufficient. Here, we report the realization of strongly correlated artificial graphene and the observation of the relativistic Mott transition in twisted WSe2 tetralayers. Using magneto transport, we show that the first $\Gamma$-valley moir\'e valence band mimics the low-energy graphene band structure. At half-band filling, the system exhibits hallmarks of massless Dirac fermions, including an anomalous Landau fan originated from a $\pi$-Berry phase and a square-root density dependence of the cyclotron mass. We tune the interaction across the semimetal-insulator transition by reducing the twist angle below about 2.7 degrees. The emergent insulator is compatible with an antiferromagnetic Mott insulator. Our results open the possibility of studying strongly correlated Dirac fermions in a condensed matter system.