Transport in the electron-glass under energy pumping

The conductance G of In₂O_3-x films in the hopping regime has been measured as function of time for a fixed temperature and at various electric fields F. When F is switched at t = 0 from F₁ to F₂2 > F₁ the conductance increases reflecting the non-Ohmic nature of field assisted hopping. However, G(F₂, t ≥ 0) is observed to be non-stationary - it increases with time in a sluggish manner. After F₂ is re-adjusted to F₁, the conductance slowly approaches its equilibrium value. The latter is presumably the slow relaxation process previously reported to occur in electron glasses excited far from equilibrium. The magnitudes of these non-ergodic effects depend on F and vanish for F < F*, the field below which G is Ohmic. The temporal evolution of G(F₂) is ascribed to the slow increase of the electron energy due to the action of F.