Quantum critical "opalescence" around metal-insulator transitions

TL;DR

This paper explores quantum critical phenomena near metal-insulator transitions, revealing unconventional universality and emergent phenomena linked to diverging density fluctuations, with implications for understanding correlated metals and superconductors.

Contribution

It provides a microscopic theory of quantum criticality in two dimensions, challenging traditional phase transition frameworks and explaining recent experimental findings in correlated materials.

Findings

Identifies unconventional universality in quantum criticality.

Connects diverging density fluctuations to emergent phenomena.

Accounts for critical behavior in organic conductors.

Abstract

Divergent carrier-density fluctuations equivalent to the critical opalescence of gas-liquid transitions emerge around a metal-insulator critical point at a finite temperature. In contrast to the gas-liquid transitions, however, the critical temperature can be lowered to zero, which offers a challenging quantum phase transition. We present a microscopic description of such quantum critical phenomena in two dimensions. The conventional scheme of phase transitions by Ginzburg, Landau and Wilson is violated and an unconventional universality appears. It offers a clear insight into the criticalities of metal-insulator transitions associated with Mott or charge-order transitions. Fermi degeneracy involving the diverging density fluctuations generates emergent phenomena near the endpoint of the first-order transition and must shed new light on remarkable phenomena found in correlated metals like unconventional cuprate superconductors. It indeed accounts for otherwise puzzling criticality of the Mott transition recently discovered in an organic conductor. We propose to measure enhanced dielectric fluctuations at small wavenumbers by accurate probes.