Violation of Kohler's Rule in the Normal-State Magnetoresistance ofYBa2Cu3O7−

The normal-state magnetoresistance (MR) $\ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho}$ of 90-K and 60-K ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ and ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ $(x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.17)$ has been measured in the longitudinal (field H parallel to current J) and transverse (H $\ensuremath{\Vert}$ c) geometries, with J in-plane. In all cases, the orbital component of the MR displays a temperature dependence that strongly violates Kohler's rule. We show that the classical orbital MR measures the variance of a local Hall angle $\ensuremath{\theta}(s)$ around the Fermi surface. The anomalous transverse MR in these cuprates is closely related to the temperature dependence of the Hall angle.