Superconductivity of SrTiO

Superconducting SrTiO _{3 - δ} was obtained by annealing single crystalline SrTiO₃ samples in ultra high vacuum. An analysis of the V ( I ) characteristics revealed very small critical currents I _c which can be traced back to an unavoidable doping inhomogeneity. R ( T ) curves were measured for a range of magnetic fields B at I ≪ I _c , thereby probing only the sample regions with the highest doping level. The resulting curves B _c2 ( T ) show upward curvature, both at small and strong doping. These results are discussed in the context of bipolaronic and conventional superconductivity with Fermi surface anisotropy. We conclude that the special superconducting properties of SrTiO _{3 - δ} can be related to its Fermi surface and compare this finding with properties of the recently discovered superconductor MgB₂. Received 4 December 2002 / Received in final form 10 March 2003 Published online 23 May 2003 RID="a" ID="a"e-mail: jourdan@uni-mainz.de