'Taxonomy' of Electron Glasses

TL;DR

This paper investigates the AC conductivity of electron glasses in silicon, revealing a sharp crossover from Coulomb glass to Fermi glass behavior that challenges existing theories and proposes a new classification scheme.

Contribution

It provides the first detailed measurements of AC conductivity in the quantum limit and introduces a new classification scheme for electron glasses based on experimental data.

Findings

Observed a sharp crossover in frequency dependence of conductivity.

Crossover energy aligns with Coulomb interaction energy estimates.

Proposed a general classification scheme for electron glasses.

Abstract

We report measurements of the real and imaginary parts of the AC conductivity in the quantum limit, \hbar \omega > k_B T of insulating nominally uncompensated n-type silicon. The observed frequency dependence shows evidence for a crossover from interacting Coulomb glass-like behavior at lower energies to non-interacting Fermi glass-like behavior at higher energies across a broad doping range. The crossover is sharper than predicted and cannot be described by any existing theories. Despite this, the measured crossover energy can be compared to the theoretically predicted Coulomb interaction energy and reasonable estimates of the localization length obtained from it. Based on a comparison with the amorphous semiconductor NbSi, we obtain a general classification scheme for electrodynamics of electron glasses.