Continuous Mott transition in semiconductor moir\'e superlattices

TL;DR

This study demonstrates a continuous Mott metal-insulator transition in a semiconductor moiré superlattice, revealing quantum criticality, diverging effective mass, and no magnetic order, consistent with a universal critical theory in two dimensions.

Contribution

It provides the first experimental observation of a continuous Mott transition in a controllable 2D semiconductor moiré system, supporting the universal critical theory.

Findings

Observation of a continuous MIT driven by electronic interactions.

Scaling behavior indicating quantum criticality near the transition.

Absence of long-range magnetic order down to low temperatures.

Abstract

The evolution of a Landau Fermi liquid into a nonmagnetic Mott insulator with increasing electronic interactions is one of the most puzzling quantum phase transitions in physics. The vicinity of the transition is believed to host exotic states of matter such as quantum spin liquids, exciton condensates and unconventional superconductivity. Semiconductor moir\'e materials realize a highly controllable Hubbard model simulator on a triangular lattice, providing a unique opportunity to drive a metal-insulator transition (MIT) via continuous tuning of the electronic interactions. Here, by electrically tuning the effective interaction strength in MoTe2/WSe2 moir\'e superlattices, we observe a continuous MIT at a fixed filling of one electron per unit cell. The existence of quantum criticality is supported by the scaling behavior of the resistance, a continuously vanishing charge-gap as the critical point is approached from the insulating side, and a diverging quasiparticle effective mass from the metallic side. We also observe a smooth evolution of the low-temperature magnetic susceptibility across the MIT and find no evidence of long-range magnetic order down to ~ 5% of the Curie-Weiss temperature. The results signal an abundance of low-energy spinful excitations on the insulating side that is further corroborated by the presence of the Pomeranchuk effect on the metallic side. Our results are consistent with the universal critical theory of a continuous MIT from a Landau Fermi liquid to a nonmagnetic Mott insulator in two dimensions.