Variable-range hopping in InP close to the metal-insulator transition

Analysis of conductivity data taken over the temperature range 4.2-0.05 K for a compensated sample of InP on the insulating side of, but very close to, the metal-insulator transition in terms of the relation sigma = sigma 0 exp(-(T 0 /T) s ) gives s=0.25 instead of s=0.5 previously obtained for a sample at some distance from the transition. Application of a small magnetic field produces behavior characteristic of the metallic regime and so confirms the phase diagram proposed by Shapiro.