Observation oflogσ∼T−12in Three-Dimensional Energy-Band Tails

Detailed measurements of the conductivity in controlled-occupancy energy-band tails of isotropic bulk material at low temperatutes (<20 K) are found to be accurately described by the relation $log\sigma \sim T^{\frac{-1\mathrm{}}{2}}$. The only theory that predicts such a relation applies to one-dimensional conduction, not three. It is suggested that these results may reflect the filamentary character of electron transport in random potentials.