Pressure dependence of out-of-plane conduction in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$

Pressure dependence of out-of-plane resistivity ${\mathrm{\rho }}_{\mathit{c}}$ has been investigated in an optimally-doped high-${\mathit{T}}_{\mathit{c}}$ cuprate ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$. By applying pressure, we found a drastic decrease in ${\mathrm{\rho }}_{\mathit{c}}$ which reaches 50% at P=8 GPa. This surprisingly large P dependence implies that the thermal contraction along the c axis is significantly reflected in the ${\mathrm{\rho }}_{\mathit{c}}$(T) curve, leading to a metal-like term; hence ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ is essentially characterized as a two-dimensional metal modified with nonmetallic conduction between ${\mathrm{CuO}}_2$ layers. Tunneling is suggested for a possible mechanism for ${\mathrm{\rho }}_{\mathit{c}}$. © 1996 The American Physical Society.