Depinning transition in Mott-Anderson insulators

We have studied the I-V curves of amorphous insulators at very low temperature which exhibit a crossover from variable range hopping to a low-temperature activation law. Around a critical voltage ${\mathit{V}}_{\mathit{c}}$, the current increases by several orders of magnitude. This is interpreted as resulting from an interplay between Coulomb interactions and disorder: below ${\mathit{V}}_{\mathit{c}}$ charges are collectively ‘‘pinned,’’ while above ${\mathit{V}}_{\mathit{c}}$ free charges exist. We find a critical scaling of the I-V curves near ${\mathit{V}}_{\mathit{c}}$, at least when hysteretic effects can be neglected. © 1996 The American Physical Society.