Role of two-dimensional electronic state in superconductivity in La${}_{2-x}$Sr${}_x$CuO${}_4$

We have measured out-of-plane resistivity ${\rho }_c$ for La${}_{2-x}$Sr${}_x$CuO${}_4$ under anisotropic pressure. c-axis compression, which decreases ${\rho }_c$, reduces $T_{\mathrm{c}}$ drastically, whereas c-axis extention, which increases ${\rho }_c$, enhances $T_{\mathrm{c}}$ from 38K at ambient pressure to 51.6K at 8GPa. We find that the variation of $T_{\mathrm{c}}$ scales as a function of ${\rho }_c$, and that the c-axis pressure coefficient is much stronger than the ab-axis one. These imply that $T_{\mathrm{c}}$ depends primarily on the interlayer, rather than the in-plane, lattice parameter.