Disorder-driven metal-insulator transitions in deformable lattices.

Simone Fratini,

Institut Neel, CNRS, Grenoble, France

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 the Anderson localization effects on the same footing. We identify an intermediate "poor conductor" 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. The solution of this long-standing experimental puzzle is found in revealing significant temperature-induced rearrangements of electronic states, due to enhanced interaction effects in the vicinity of the disorder-driven MIT.