Theory of a Continuous Bandwidth-tuned Wigner-Mott Transition

Abstract

We develop a theory for a continuous bandwidth-tuned transition at fixed 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 (MIT) and analyze the example of a bandwidth-tuned transition at a filling, ν = 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 moiré transition metal dichalcogenide materials.

How to Recognize the Universal Aspects of Mott Criticality?

“…Concerning quantum critical scaling, it is interesting that this theory proposes the emergence of two crossover temperature scales, both of which vanish at the transition. We finally mention that a similar spin-charge separation theory has been very recently proposed to also describe the Wigner-Mott transition in TMD bilayers, where a possible role of charge fluctuations has also been discussed for the metallic side [60,61].…”

Quantum noise spectroscopy of dynamical critical phenomena

“…For example, pressure-driven quantum critical points in two dimensional materials, such as FeSe [84,85], as well as straintuned magnetic transitions in monolayer metallic halides, such as the aforementioned CrI 3 [86], can be accessed by directly incorporating the NV center into diamond anvil cells [51,57,87], while magnetic domain formation can be imaged in situ by directly incorporating V − B into the hBN that encapsulates many 2D materials [88,89]. Simultaneously, the detection and characterization of spin and charge fluctuations can elucidate the nature of the magnetic order in twisted bilayer graphene [90][91][92][93][94][95][96], as well as shed light into the continuous Mott transition recently observed in moiré transition metal dichalcogenides [83,97,98].…”