Disorder-driven metal-insulator transitions in deformable lattices

TL;DR

This paper demonstrates that electron-phonon interactions in deformable lattices fundamentally alter the disorder-driven metal-insulator transition, leading to a mobility gap and a 'bad insulator' regime with distinctive transport properties.

Contribution

It provides a microscopic framework treating lattice deformations and Anderson localization simultaneously, revealing how modest electron-phonon interactions significantly modify the transition.

Findings

Disorder and electron-phonon interactions jointly influence the MIT.

A mobility gap emerges at strong disorder with electron-phonon coupling.

Identification of a 'bad insulator' regime with high resistivity and negative temperature coefficient.

Abstract

We show that in presence of a deformable lattice potential, the nature of the disorder-driven metal-insulator transition (MIT) is fundamentally changed with respect to the non-interacting (Anderson) scenario. For strong disorder, even a modest electron-phonon interaction is found to dramatically renormalize the random potential, opening a mobility gap at the Fermi energy. This process, which reflects disorder-enhanced polaron formation, is here given a microscopic basis by treating the lattice deformations and Anderson localization effects on the same footing. We identify an intermediate "bad insulator" transport regime which displays resistivity values exceeding the Mott-Ioffe-Regel limit and with a negative temperature coefficient, as often observed in strongly disordered metals. Our calculations reveal that this behavior originates from significant temperature-induced rearrangements of electronic states due to enhanced interaction effects close to the disorder-driven MIT.