Conductance Fluctuations in a Disordered Double-Barrier Junction

TL;DR

This paper investigates how disorder affects quantum conductance in a double-barrier junction, revealing universal conductance fluctuations and their dependence on junction symmetry and resistance ratios.

Contribution

It provides analytical and numerical analysis showing that disorder induces universal conductance fluctuations in double-barrier junctions, with specific dependence on symmetry and resistance ratios.

Findings

Conductance fluctuations are of universal magnitude e^2/h.

Fluctuations depend on the ratio of tunnel resistances and symmetry.

Strong mode-mixing causes mesoscopic conductance fluctuations.

Abstract

We consider the effect of disorder on coherent tunneling through two barriers in series, in the regime of overlapping transmission resonances. We present analytical calculations (using random-matrix theory) and numerical simulations (on a lattice) to show that strong mode-mixing in the inter-barrier region induces mesoscopic fluctuations in the conductance $G$ of universal magnitude $e^2/h$ for a symmetric junction. For an asymmetric junction, the root-mean-square fluctuations depend on the ratio $\nu$ of the two tunnel resistances according to ${rms} G = (4e^2/h)\beta^{-1/2} \nu(1+\nu)^{-2}$, where $\beta = 1 (2)$ in the presence (absence) of time-reversal symmetry.