We report measurements of the normal state magnetoresistance (MR) from 30 to 340 K in fields B up to 13 T for single crystals of overdoped ${\mathrm{Tl}}_2{\mathrm{Ba}}_2{\mathrm{CuO}}_6$ $\left(T_c\le 25\mathrm{K}\right)$. For out-of-plane current flow, the transverse MR $\Delta {\rho }_c/{\rho }_c$ is large and positive. On rotating B within the a-b plane, $\Delta {\rho }_c/{\rho }_c$ exhibits a striking anisotropy with fourfold symmetry. The amplitude of this effect increases as $B^4$ and the maximum MR occurs for B along the [110] crystallographic directions, i.e., at 45° to the Cu-O-Cu bonds. This the first direct evidence for anisotropy of the in-plane mean free path in the cuprates.

• Received 24 July 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.122