Quantum electron glasses and electron assisted hopping

Markus Mueller, Harvard University

Abstract: Insulators close to the metal insulator transition exhibit interesting collective electronic phenomena which are still quite poorly understood. A prominent feature in such systems is the purely electronic nature of activated transport apparent in experiments, which is inconsistent with the theory of phonon-assisted hopping conduction and thus remained an unexplained puzzle for decades. In this talk I will address this problem for Anderson insulators with a single-particle localization length much larger than the mean distance between electrons. Under these circumstances Coulomb interactions drive the electrons into a strongly correlated quantum glass phase with non-trivial collective behavior. I will show that a typical metastable state exhibits a gapless spectrum of collective excitations which act as a bath with which individual electrons can exchange energy. In 2D systems, this resultys in a hopping transport mechanism with a nearly universal pre-exponential factor of order e^2/h, in good agreement with many recent experiments.