Interlayer Tunneling Spectroscopy for Slightly OverdopedBi2Sr2CaCu2O8+δ

We have measured the interlayer tunneling characteristics of slightly overdoped $\mathrm{Bi}{}_2\mathrm{Si}{}_2\mathrm{CaCu}{}_2{\mathrm{O}}_{8+\delta }$ in the $c$-axis direction from 10 to 220 K by using very thin mesas containing approximately ten $\mathrm{CuO}{}_2$ double layers. The superconducting gap $2\Delta$ is 50 meV at 10 K and shows a temperature ( $T$) dependence similar to that of the BCS theory. A pseudogap evolves below 150 K, where the $c$-axis resistivity ${\rho }_c$ is semiconducting. The normal-state tunneling resistance $R_N$ shows a linear $T$ dependence down to $T_c$, exhibits an abrupt decrease at $T_c$, and saturates at low $T$. This reflects scattering arising from an electronic interaction that is relevant to the high- $T_c$ superconductivity.