Tunnel-like characteristics of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$/${\mathrm{CeO}}_2$/${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ junctions and possible evidence of excitations responsible for high-${\mathit{T}}_{\mathit{c}}$ superconductivity

The tunnel-like characteristics observed in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$/${\mathrm{CeO}}_2$/${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ heteroepitaxial junctions fabricated by a vacuum evaporation technique are reported. Pronounced gaplike structures around 9 and 20 mV, which depend on temperature and the additional structures at high-bias voltages (40–180 mV), are observable. The latter structures emerge rapidly near ${\mathit{T}}_{\mathit{c}}$ and may reflect the density of states of the possible excitations responsible for high-${\mathit{T}}_{\mathit{c}}$ superconductivity. The data suggest that the excitations other than phonons are possible.