Electron tunneling study of the normal and superconducting states of ${\mathrm{Bi}}_{1.7}$${\mathrm{Pb}}_{0.3}$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{x}}$

We report point-contact tunneling into single crystals of ${\mathrm{Bi}}_{1.7}$ ${\mathrm{Pb}}_{0.3}$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{x}}$. The current-voltage characteristics I(V) are quite symmetrical and very reproducible, exhibit a decreasing conductance at high voltages, and can be fitted with a smeared BCS density of states (DOS). We are necessarily led to conclude that the normal-state conductance, in the absence of parabolic-tunneling-barrier effects, has a peak near the Fermi energy, and we speculate that it could be due to the normal-state DOS of ${\mathrm{Bi}}_{1.7}$ ${\mathrm{Pb}}_{0.3}$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{x}}$.