Is disorder a friend or a foe to melting of Wigner-Mott insulators?

TL;DR

This paper investigates how disorder influences the stability and melting transition of Wigner-Mott insulators, revealing that disorder can both stabilize Wigner lattices at higher densities and smear the melting transition, leading to coexistence of phases.

Contribution

It provides a microscopic model analysis showing disorder's dual role in stabilizing Wigner lattices and altering melting behavior in two-dimensional systems.

Findings

Disorder suppresses gapless shear density fluctuations, stabilizing Wigner lattices at higher densities.

Disorder smears the melting transition, causing coexistence of solid-like and liquid-like regions.

Disorder effectively increases the stability of Wigner-Mott solids in two dimensions.

Abstract

Wigner crystals are extremely fragile, which is shown to result from very strong geometric frustration germane to long-range Coulomb interactions. Physically, this is manifested by a very small characteristic energy scale for shear density fluctuations, which are gapless excitations in a translationally invariant system. The presence of disorder, however, breaks translational invariance, thus suppressing gapless excitations and pushing them to higher density. We illustrate this general principle by explicit microscopic model calculations, showing that this mechanism very effectively stabilizes disordered Wigner lattices to much higher temperatures and densities than in the clean limit. On the other hand, we argue that in two dimensions disorder significantly ``smears" the melting transition, producing spatial coexistence of solid-like and liquid-like regions -- just as recently observed in STM experiments. Our results paint a new physical picture for melting of Wigner-Mott solids in two dimensions, corresponding to a Mott-Hubbard model with spatially varying local electronic bandwidth.