Negative magnetoresistance in variable-range-hopping conduction

The orbital mechanism of negative magnetoresistance of variable-range-hopping conductivity is reconsidered by numerical simulations and qualitative arguments. At small magnetic fields the positive magnetic-field corrections to the localization length in two-dimensional samples are universal in the sense that they are independent of the details of the scattering potential (impurity concentration, amplitude of scattering, and proximity to the metal-insulator transition). Implications of these results to transport properties on the dielectric side of the superconductor-insulator transition are discussed.