Strong Magnetoresistance Induced by Long-Range Disorder

We calculate the semiclassical magnetoresistivity ${\rho }_{\mathrm{xx}}\left(B\right)$ of noninteracting fermions in two dimensions moving in a weak and smoothly varying random potential or random magnetic field. We demonstrate that in a broad range of magnetic fields the non-Markovian character of the transport leads to a strong positive magnetoresistance. The effect is especially pronounced in the case of a random magnetic field where ${\rho }_{\mathrm{xx}}\left(B\right)$ becomes parametrically much larger than its $B=0\mathrm{}$ value.