Relaxation dynamics in quantum electron-glasses

It is experimentally shown that, depending on the carrier-concentration of the system $n$, the dynamics of electron-glasses either \textit{slows down }with increasing temperature or it is \textit{independent} of it. This also correlates with the dependence of a typical relaxation time (or `viscosity') on $n$. These linked features are argued to be consistent with a model for dissipative tunneling. The slow relaxation of the electron glass may emerge then as a manifestation of friction in a many-body quantum system. Our considerations may also explain why strongly-localized granular metals are likely to show electron-glass effects while semiconductors are not.