The quasiparticle density of states is discussed in the framework of d-wave superconductivity, and the corresponding superconductor-insulator-superconductor tunneling conductivity σ(V) is obtained. We find a quadratic increase of σ(V) at low voltage and two maxima at higher voltage. These features are in qualitative agreement with recent experimental findings of Forro et al. An s-wave state also gives rise to a double-peak structure, but no quadratic low-voltage behavior is found.

• Received 3 December 1991

DOI:https://doi.org/10.1103/PhysRevB.45.7397