We have measured the anisotropic magnetoresistivity tensor of single-crystal ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ in the normal and in the mixed state. For magnetic fields applied perpendicular to the Cu-O (a-b) planes, the out-of-plane (c-axis) resistivity displays a huge magnetic enhancement, and a large apparent depression in the resistively measured transition temperature ${\mathit{T}}_{\mathit{c}}$ (c axis). No such depression is observed in ${\mathit{T}}_{\mathit{c}}$(a-b plane). Although these results suggest a field-induced anisotropy in ${\mathit{T}}_{\mathit{c}}$, we propose an alternate model of novel Lorentz-force-independent fluctuation-induced dissipation in the mixed state. The model may also account for the anomalous anisotropic magnetoresistance observed in layered low-${\mathit{T}}_{\mathit{c}}$ superconductors.

• Received 26 October 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.2164