Suppression of inelastic electron-electron scattering in Anderson   Insulators
  We report on measurements of absorption from applied ac fields in Anderson-localized indium-oxide films. The absorption shows a roll-off at a frequency that is much smaller than the electron-electron scattering rate measured at the same temperature in diffusive samples of this material. These results are interpreted as evidence for discreteness of the energy spectrum. 
Z. Ovadyahu
cond-mat.str-el