title: Electrodynamics of a Coulomb glass in n-type silicon.
abstract: Measurements of the complex frequency dependent conductivity of uncompensated n-type silicon are reported. The experiments are done in the quantum limit, variant Planck's over 2pi omega>k(B)T, across a broad doping range on the insulating side of the metal-insulator transition. The low energy linear frequency dependence is consistent with theories of a Coulomb glass, but discrepancies exist in the relative magnitudes of the complex components. At higher energies we observe a crossover to a quadratic frequency dependence that is sharper than expected. The concentration dependence gives evidence that the Coulomb interaction energy is the energy scale that determines this crossover.
authors.affiliation: Department of Physics and Astronomy, University of California-Los Angeles, 90095, USA.
authors.forename: E
authors.initials: E
authors.lastname: Helgren
authors.forename: N P
authors.initials: NP
authors.lastname: Armitage
authors.forename: G
authors.initials: G
authors.lastname: Grüner