Low-temperature transport properties ofCd0.91Mn0.09Te:In and evidence for a magnetic hard gap in the density of states

A family of resistivity curves, with different carrier concentrations, is obtained in a single sample of the dilute magnetic persistent photoconductor ${\mathrm{Cd}}_{0.91}$ ${\mathrm{Mn}}_{0.09}$Te:In. These curves exhibit a crossover from an exp(${\mathit{T}}_0$/T${)}^{1/2}$ form for variable-range hopping with interactions to an exp(${\mathit{E}}_{\mathit{H}}$/T) form, upon reducing temperature. All data scale onto a single curve. The energy ${\mathit{E}}_{\mathit{H}}$ is associated with a hard gap in the density of states which is magnetic in origin. The localization length is found to have the same critical behavior as the dielectric constant, on approaching the insulator-metal transition.