S-wave Superconductivity in Optimally Doped SrTi${}_{1-x}$Nb${}_x$O${}_3$ Unveiled by Electron Irradiation

Abstract

We report on a study of electric resistivity and magnetic susceptibility measurements in electron irradiated SrTi${}_{0.987}$Nb${}_{0.013}$O${}_3$ single crystals. Point-like defects, induced by electron irradiation, lead to an almost threefold enhancement of the residual resistivity, but barely affect the superconducting critical temperature ($T_c$). The pertinence of Anderson's theorem provides strong evidence for a s-wave superconducting order parameter. Stronger scattering leads to a reduction of the effective coherence length ($\hat{I}¾$) and the deduced coherence length in the clean limit ($\hat{I}{¾}_0$) is around the BCS coherence length ($\hat{I}{¾}_{BCS}$). Combined with thermal conductivity data pointing to multiple nodeless gaps, the current results identify optimally doped SrTi${}_{1-x}$Nb${}_x$O${}_3$ as a multi-band s-wave superconductor.

5 pages, 4 figures