Tunneling measurements have been performed on Nb-doped and reduced superconducting SrTi${\mathrm{O}}_3$. Beyond a certain carrier concentration, when a second conduction band gets filled, a distinctive double-gap structure is observed in Nb-doped samples. Its sharpness and anomalous temperature dependence can be related to the onset of two-band superconductivity in accordance with theoretical expectations. The observation of a single gap $\Delta \simeq 1.76 k{T}_c$ in reduced SrTi${\mathrm{O}}_3$ is attributed to enhanced interband scattering.

• Received 8 April 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.1352