Nonmonotonic magnetic field and density dependence of in-plane magnetoresistance in dilute two-dimensional holes in G a A s / A l x Ga 1 − x As

We studied low temperature $(T=50$ mK) in-plane magnetoresistance of a dilute two-dimensional hole system in GaAs/AlGaAs heterostructure that exhibits an apparent metal-insulator transition. We found an anisotropic magnetoresistance, which changes dramatically at high in-plane fields ${(B}_{\ensuremath{\Vert}}\ensuremath{\gtrsim}5$ T) as the hole density is varied. At high densities where the system behaves metallic at ${B}_{\ensuremath{\Vert}}=0,$ the transverse magnetoresistance is larger than the longitudinal magnetoresistance. With decreasing the hole density the difference becomes progressively smaller, and at densities near the ``critical'' density and lower, the longitudinal magnetoresistance becomes larger than the transverse magnetoresistance.