Finite frequency scaling of hopping conductivity in n-InSb

Conductivity measurements on three disc-shaped n-InSb samples were carried out in magnetic fields up to 70 kG at temperatures down to 40 mK and over a frequency range of 0–105 Hz. In the hopping-conduction region the a.c. and d.c. conductivities were found to scale according to:σ(ω, T)/σ(0, T) = f [AωT/σT(0, T)], where ~ωT and ~σT are normalized values and f is a universal function obtained by Summerfield. The parameter -log10 A is found to be 3·0±0·2, a value which is predicted by theory for some semiconductor materials with a constant density of states at the Fermi level.