Anomalous scaling of conductance cumulants in one-dimensional Anderson localization

TL;DR

This paper analytically investigates the behavior of conductance cumulants in one-dimensional Anderson localization, revealing anomalies at the band center and deriving new approximations to match numerical results.

Contribution

It introduces an improved Born approximation for reflection amplitudes that accurately captures conductance cumulant anomalies in the localized regime.

Findings

Exact expressions for mean and variance of ln g in the localized regime.

Identification of a quadratic anomaly term in the variance at the band center.

Linear relation between variance and mean of ln g at generic energies.

Abstract

The mean and the variance of the logarithm of the conductance ($ln g$) in the localized regime in the one-dimensional Anderson model are calculated analytically for weak disorder, starting from the recursion relations for the complex reflection- and transmission amplitudes. The exact recursion relation for the reflection amplitudes is approximated by improved Born approximation forms which ensure that averaged reflection coefficients tend asymptotically to unity in the localized regime, for chain lengths $L=Na\to\infty$. In contrast the familiar Born approximation of perturbation theory would not be adapted for the localized regime since it constrains the reflection coefficient to be less than one. The proper behaviour of the reflection coefficient (and of other related reflection parameters) is responsible for various anomalies in the cumulants of $\ln g$, in particular for the well-known band center anomaly of the localization length. While a simple improved Born approximation is sufficient for studying cumulants at a generic band energy, we find that a generalized improved Born approximation is necessary to account satisfactorily for numerical results for the band center anomaly in the mean of $\ln g$. For the variance of $\ln g$ at the band center, we reveal the existence of a weak anomalous quadratic term proportional to $L^2$, besides the previously found anomaly in the linear term. At a generic band energy the variance of $\ln g$ is found to be linear in $L$ and is given by twice the mean, up to higher order corrections which are calculated. We also exhibit the $L=$independent offset terms in the variance, which strongly depend on reflection anomalies.