Interplane charge transport in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$: Spin-gap effect on in-plane and out-of-plane resistivity

We have investigated the anisotropic resistivities of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ using detwinned crystals with various oxygen contents (6.68 ≤7-y≤ 6.93). The out-of-plane resistivity ${\mathrm{\rho }}_{\mathit{c}}$ shows a crossover from high-T metallic to low-T semiconducting behavior while the in-plane resistivity ${\mathrm{\rho }}_{\mathit{a}}$ deviates in the low-T region from T-linear dependence. We find that the crossover in ${\mathrm{\rho }}_{\mathit{c}}$ is linked with the onset of nonlinearity in ${\mathrm{\rho }}_{\mathit{a}}$, which seems to be associated with the ‘‘spin gap’’ suggested by neutron and NMR studies.