Voltage fluctuations in mesoscopic conductors with single-channel leads: Electronic speckle patterns

We study theoretically the voltage fluctuations of a mesoscopic disordered conductor that is connected to single-channel current leads in the four-probe configuration. We find dramatically enhanced voltage fluctuations, which are interpreted as the electronic equivalent of laser speckle patterns. We also compute the correlation functions of the electrochemical potential and the current density inside the sample, which provide a general description for transport with single-channel leads (for either the current leads or the voltage leads, or for both)