Crossover phenomenon for hopping conduction in strong magnetic fields

Abstract

We find that strong magnetic fields reduce the effectiveness of the Coulomb gap in determining the variable-range-hopping (VRH) resistivity \ensuremath{\rho}. We propose a crossover phenomenon characterized by a temperature ${\mathit{T}}_{\mathit{c}}$ with the Coulomb gap affecting the VRH resistivity only below ${\mathit{T}}_{\mathit{c}}$. The value of ${\mathit{T}}_{\mathit{c}}$ decreases as the magnetic field increases. Our theoretical model explains the observed crossover from a ln\ensuremath{\rho}(H=0)\ensuremath{\propto}${\mathit{T}}^{\mathrm{\ensuremath{-}}1/2}$ law to a ln\ensuremath{\rho}(H)\ensuremath{\propto}[${\mathit{T}}_{0}$(H)/T${]}^{1/3}$ law with ${\mathit{T}}_{0}$\ensuremath{\propto}H.