Electron tunneling and the energy gap in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_x$

Results of electron tunneling on single crystals of the ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_x$ superconductor are reported. The junctions show a gap structure with $\Delta \approx 25$ meV, whose temperature dependence exhibits a qualitatively Bardeen-Cooper-Schrieffer-like behavior with a gap-closing $T_c\approx 81-85$ K. Comparisons of these tunneling spectra to those obtained on $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ are made. Evidence that $\frac{2\Delta }{k{T}_c}\sim 7$ for both ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_x$ and $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ is also discussed.