'Taxonomy' of Electron Glasses

摘要

We report measurements of the real and imaginary parts of the AC conductivityin the quantum limit, \hbar \omega > k_B T of insulating nominallyuncompensated n-type silicon. The observed frequency dependence shows evidencefor a crossover from interacting Coulomb glass-like behavior at lower energiesto non-interacting Fermi glass-like behavior at higher energies across a broaddoping range. The crossover is sharper than predicted and cannot be describedby any existing theories. Despite this, the measured crossover energy can becompared to the theoretically predicted Coulomb interaction energy andreasonable estimates of the localization length obtained from it. Based on acomparison with the amorphous semiconductor NbSi, we obtain a generalclassification scheme for electrodynamics of electron glasses.