Abstract

We have fabricated tunnel junctions between chemically etched single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and evaporated metal counterelectrodes which exhibit reproducible characteristics. Above the bulk critical temperature of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$, ${T}_{c}$, the conductance, G(V), has a linear dependence with voltage and has some asymmetry. Below ${T}_{c}$, additional structure associated with the superconductivity appears in G(V). At T\ensuremath{\ll}${T}_{c}$ there is a reproducible, finite, zero-bias conductance which suggests that there are states at the Fermi energy superconducting ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. Junctions with Pb, Sn, Bi, Sb, PbBI, and Au counterelectrodes all show qualitatively similar behavior.