Conductance fluctuations due to motion of a single impurity in the localized regime

We analyze mesoscopic conductance fluctuations due to the motion of a single impurity in the localized regime, using a random-matrix argument and extensive numerical simulations. We find that in phase-coherent systems, moving a single impurity gives rise to a very wide distribution of conductance fluctuations. The single-impurity-motion-induced variance 〈[ln(g/g')]²〉 is characterized by a value of order unity, almost independent of system parameters and dimensionality for a wide range of values of 〈-ln(g)〉{}1. Relevance of this result for the study of resonances in the tunneling regime and for the noise measurements in macroscopic systems in the Mott variable-range hopping regime is discussed.