Nearly Localized States in Weakly Disordered Conductor

Abstract

The time dispersion of the averaged conductance $G(t)$ of a mesoscopic sample is calculated in the long time limit when $t$ is much larger than the diffusion travelling time $ t_D$. In this case the functional integral in the effective supersymmetric field theory is determined by the saddle point contribution. If $t$ is shorter than the inverse level spacing $\Delta$ ($\Delta t / \hbar \ll 1$), then $G(t)$ decays as $\exp[-t/t_D]$. In the ultra-long time limit ($\Delta t / \hbar \gg 1$) the conductance $G(t)$ is determined by the electron states that are poorly connected with the outside leads. The probability to find such a state decreases more slowly than any exponential funcion as $t$ tends to infinity. It is worth mentioning, that the saddle point equation looks very similar to the well known Eilenberger equation in the theory of dirty superconductors.