Crossover phenomenon for hopping conduction in strong magnetic fields

We find that strong magnetic fields reduce the effectiveness of the Coulomb gap in determining the variable-range-hopping (VRH) resistivity ρ. 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 lnρ(H=0)∝${\mathit{T}}^{\mathrm{-}1/2}$ law to a lnρ(H)∝[${\mathit{T}}_0$(H)/T${]}^{1/3}$ law with ${\mathit{T}}_0$∝H.