Landau-Ginzburg Theory for Anderson localization

TL;DR

This paper extends the Typical Medium Theory for Anderson localization by incorporating spatial correlations through a Landau approach, explaining recent STM experimental observations in disordered magnetic semiconductors.

Contribution

It introduces a self-consistent Landau theory capturing spatial fluctuations of the order parameter in Anderson localization, linking theory with STM experiments.

Findings

Reproduces STM observations of spatially fluctuating wave functions.

Accounts for pseudogap formation and LDOS autocorrelation features.

Explains energy-dependent correlation length near the metal-insulator transition.

Abstract

The Typical Medium Theory provides conceptually the simplest order parameter description of Anderson localization by self-consistently calculating the geometrically-averaged (typical) local density of states (LDOS). Here we show how spatial correlations can also be captured within such a self-consistent theory, by utilizing the standard Landau method of allowing for (slow) spatial fluctuations of the order parameter, and performing an appropriate gradient expansion. Our theoretical results provide insight into recent STM experiments, which were used to visualize the spatially fluctuating electronic wave functions near the metal insulator transition in $Ga_{1-x}Mn_{x}As.$ We show that, within our theory, all features of the experiment can be accounted for by considering a model of disorder renormalized by long-range Coulomb interactions. This includes the pseudogap formation, the $C(R)\sim\frac{1}{R}$ form of the LDOS autocorrelations function, and the $\zeta\sim\frac{1}{E}$ energy dependence of the correlation length at criticality.