SrTiO3 exhibits a superconducting dome upon doping with Nb, with a maximum critical temperature \mbox{Tc≈0.4~K}. Using microwave stripline resonators at frequencies from 2 to 23~GHz and temperatures down to 0.02~K, we probe the low-energy optical response of superconducting SrTiO3 with charge carrier concentration from 0.3 to 2.2×1020~cm−3, covering the majority of the superconducting dome. We find single-gap electrodynamics even though several electronic bands are superconducting. This is explained by a single energy gap 2Δ due to gap homogenization over the Fermi surface consistent with the low level of defect scattering in Nb-doped SrTiO3. Furthermore, we determine Tc, 2Δ, and the superfluid density as a function of charge carrier concentration, and all three quantities exhibit the characteristic dome shape.
@article{arxiv.1703.04716,
title = {Single-gap superconductivity and dome of superfluid density in Nb-doped SrTiO3},
author = {Markus Thiemann and Manfred H. Beutel and Martin Dressel and Nicholas R. Lee-Hone and David M. Broun and Evangelos Fillis-Tsirakis and Hans Boschker and Jochen Mannhart and Marc Scheffler},
journal= {arXiv preprint arXiv:1703.04716},
year = {2018}
}