Theory of a continuous bandwidth-tuned Wigner-Mott transition

TL;DR

This paper develops a theoretical framework for a continuous transition from a metal to a Wigner-Mott insulator with symmetry breaking, characterized by an abrupt Fermi surface disappearance and a continuous charge gap vanishing, relevant to moiré materials.

Contribution

The paper introduces a novel theory for continuous bandwidth-tuned metal-insulator transitions with symmetry breaking and neutral spinon Fermi surfaces, supported by a large-N analysis and experimental relevance.

Findings

Fermi surface disappears abruptly at the transition from the metallic side.

Charge gap and order parameters vanish continuously from the insulating side.

The theory applies to moiré transition metal dichalcogenide materials.

Abstract

We develop a theory for a continuous bandwidth-tuned transition at fixed \textit{fractional} electron filling from a metal with a generic Fermi surface to a `Wigner-Mott' insulator that spontaneously breaks crystalline space-group symmetries. Across the quantum critical point, (i) the entire electronic Fermi surface disappears abruptly upon approaching from the metallic side, and (ii) the insulating charge gap and various order parameters associated with the spontaneously broken space-group symmetries vanish continuously upon approaching from the insulating side. Additionally, the insulating side hosts a Fermi surface of neutral spinons. We present a framework for describing such continuous metal-insulator transitions (MITs) and analyze the example of a bandwidth-tuned transition at a filling, $\nu=1/6$, for spinful electrons on the triangular lattice. By extending the theory to a certain large-$N$ limit, we provide a concrete example of such a continuous MIT and discuss numerous experimental signatures near the critical point. We place our results in the context of recent experiments in moir\'e transition metal dichalcogenide materials.