The Electron Glass in a Switchable Mirror: Relaxation, Aging and   Universality
  The rare earth hydride YH$_{3-\delta}$ can be tuned through the metal-insulator transition both by changing $\delta$ and by illumination with ultraviolet light. The transition is dominated by strong electron-electron interactions, with transport in the insulator sensitive to both a Coulomb gap and persistent quantum fluctuations. Via a systematic variation of UV illumination time, photon flux, Coulomb gap depth, and temperature, we demonstrate that polycrystalline YH$_{3-\delta}$ serves as a model system for studying the properties of the interacting electron glass. Prominent among its features are logarithmic relaxation, aging, and universal scaling of the conductivity. 
M. Lee, P. Oikonomou, P. Segalova, T.F. Rosenbaum, A.F.Th. Hoekstra   and P.B. Littlewood