Dilute superconductivity survives in bulk strontium titanate when the Fermi temperature falls well below the Debye temperature. Here, we show that the onset of the superconducting dome is dopant-dependent. When mobile electrons are introduced by removing oxygen atoms, the superconducting transition survives down to 2×1017 cm−3, but when they are brought by substituting Nb with Ti, the threshold density for superconductivity is an order of magnitude higher. Our study of quantum oscillations reveals a significant difference in the band dispersion between the dilute metals made by these doping routes and our band calculations demonstrate that the rigid band approximation does not hold when mobile electrons are introduced by oxygen vacancies. We identify the band sculpted by theses vacancies as the exclusive locus of superconducting instability in the ultra-dilute limit.
@article{arxiv.2208.09831,
title = {An electronic band sculpted by oxygen vacancies and indispensable for dilute superconductivity},
author = {Benoît Fauqué and Clément Collignon and Hyeok Yoon and Ravi and Xiao Lin and Igor Mazin and Harold Y. Hwang and Kamran Behnia},
journal= {arXiv preprint arXiv:2208.09831},
year = {2023}
}