Negative magnetoresistance in the c-axis resistivity of Bi2Sr2CaCu2O8+δ and YBa2Cu3O6+x

Abstract

The c-axis resistivity ${\mathrm{\rho }}_{\mathit{c}}$ in ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ and oxygen-reduced ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+\mathrm{x}}$ is quite sensitive to a magnetic field H. The magnetoresistance (MR) is large (1% at 14 T and 100 K), weakly anisotropic, and negative over a wide range of temperatures T above the critical temperature ${\mathit{T}}_{\mathit{c}}$. The magnitude of the MR is activated in temperature with a characteristic energy ${\mathit{U}}_{\mathit{L}}$ that varies with the oxygen content δ. We interpret the activated form of ${\mathrm{\rho }}_{\mathit{c}}$ and the negative MR in terms of a pseudogap Δ that is slightly reduced by H.