Onset of linear field dependence of the transverse magnetoresistance in a polycrystalline metal

The linear field dependence of the transverse magnetoresistance of a polycrystalline uncompensated metal with an open Fermi surface is said to arise from a contrast between extended and truly open orbits. We show that in the intermediate-field regime this is incorrect for Cu at least, where the linear dependence is initiated by the transition to the high-field condition of electrons in closed orbits.