Mechanism of Hopping Transport in Disordered Mott Insulators

By using a combination of detailed experimental studies and simple theoretical arguments, we identify a novel mechanism characterizing the hopping transport in the Mott insulating phase of Ca_2-xSrₓRuO₄ near the metal-insulator transition. The hopping exponent α shows a systematic evolution from a value of α=1/2 deeper in the insulator to the conventional Mott value α=1/3 closer to the transition. This behavior, which we argue to be a universal feature of disordered Mott systems close to the metal-insulator transition, is shown to reflect the gradual emergence of disorder-induced localized electronic states populating the Mott-Hubbard gap.