Slow dynamics of electron glasses: The role of disorder

Abstract

We examine in this work the role of disorder in contributing to the sluggish relaxation observed in intrinsic electron glasses. Our approach is guided by several empirical observations: First and foremost, Anderson localization is a pre-requisite for observing these nonequilibrium phenomena. Secondly, sluggish relaxation appears to favor Anderson insulators with relatively large Fermi energies (hence proportionally large disorder). These observations motivated us to consider a way to measure the underlying disorder in a realistic Anderson insulator. Optical studies using a series of amorphous indium oxide (${\mathrm{In}}_{x}\mathrm{O}$) establish a simple connection between carrier concentration and the disorder necessary to approach the metal-insulator transition from the insulating side. This is used to estimate the typical magnitude of the quenched potential fluctuation in the electron-glass phase of this system. The implications of our findings on the slow dynamics of Anderson insulators are discussed. In particular, the reason for the absence of a memory dip and the accompanying electron-glass effects in lightly-doped semiconductors emerges as a natural consequence of their weak disorder.