Measurements of the Complex Conductivity of NbxSi1-x Alloys on the Insulating Side of the Metal-Insulator Transition

Abstract

We have conducted temperature and frequency dependent transport measurements in amorphous Nb_x Si_{1-x} samples in the insulating regime. We find a temperature dependent dc conductivity consistent with variable range hopping in a Coulomb glass. The frequency dependent response in the millimeter-wave frequency range can be described by the expression $sigma(omega)\propto (-ıomega{)}^{a}lpha$ with the exponent somewhat smaller than one. Our ac results are not consistent with extant theories for the hopping transport.

4 pages with 3 figures; published version has a different title from original (was: "Electrodynamics in a Coulomb glass")

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