Normal-state magnetoresistance ofSr2RuO4

We report measurements of the in-plane and out-of-plane magnetoresistance (MR) of single crystals of the layered perovskite superconductor ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ ${(T}_c\approx 1\mathrm{K}).\mathrm{}$ The transverse $c$-axis MR $\Delta {\rho }_c/{\rho }_c\mathrm{}\left(B\right)\mathrm{}$ $(I\parallel c,B\parallel ab)$ varies linearly with field at low temperatures consistent with the behavior expected for a quasi-two-dimensional Fermi surface in the intermediate-field regime. $\Delta {\rho }_c/{\rho }_c\mathrm{}\left(T\right)\mathrm{}$ shows a striking temperature dependence which arises from the competing effects of two separate MR contributions. At low temperatures, $\Delta {\rho }_c/{\rho }_c$ is large and positive due to the orbital magnetoresistance of the carriers. At high temperatures, however, $\Delta {\rho }_c/{\rho }_c$ is dominated by a negative MR term that is associated with the nonmetallic out-of-plane resistivity ${\rho }_c\mathrm{}\left(T\right).$ We argue that the two contributions to $\Delta {\rho }_c/{\rho }_c\mathrm{}(B,T)\mathrm{}$ originate from separate conduction channels along the $c$ axis and that the competition between the metallic and nonmetallic channels is responsible for the unusual temperature dependence of ${\rho }_c\mathrm{}\left(T\right).$ Finally, we discuss the relevance of these findings to our current understanding of the unusual magnetoresistance of the high-$T_c$ cuprates.