Optical excitation of electron glasses

Electron glasses can be readily driven far from equilibrium by a variety of means. Several mechanisms to excite the system and their relative merits are reviewed. In this paper, we focus on the process of exciting electron glasses by interaction with near-infrared radiation. The efficiency of this protocol varies considerably among different electron glasses, but it only weakly depends on their resistance at liquid-helium temperatures. A dramatic enhancement of the excitation efficiency is observed upon doping crystalline indium oxide with Au. Some enhancement is observed also in samples doped with Pb, but this enhancement fades away with time, unlike the situation in the Au-doped samples. Several structural and analytical tools are used to characterize the changes in the materials that may be responsible for these effects. Possible routes by which high-frequency electromagnetic fields take the system far from equilibrium are discussed.