Two-band superconductivity in Nb-Doped SrTiO3

Tunneling measurements have been performed on Nb-doped and reduced superconducting SrTiO3. 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 1.76 kTc in reduced SrTiO3 is attributed to enhanced interband scattering. © 1980 The American Physical Society.