We report the influence on the superconducting critical temperature Tc in doped SrTiO3 of the substitution of the natural 16O atoms by the heavier isotope 18O. We observe that for a wide range of doping this substitution causes a strong (∼50%) enhancement of Tc. Also the magnetic critical field Hc2 is increased by a factor ∼2. Such a strong impact on Tc and Hc2, with a sign opposite to conventional superconductors, is unprecedented. The observed effect could be the consequence of strong coupling of the doped electrons to lattice vibrations (phonons), a notion which finds support in numerous optical and photo-emission studies. The unusually large size of the observed isotope effect supports a recent model for superconductivity in these materials based on strong coupling to the ferroelectric soft modes of SrTiO3.
@article{arxiv.1610.10045,
title = {Isotope effect in superconducting n-doped SrTiO$_3$},
author = {A. Stucky and G. Scheerer and Z. Ren and D. Jaccard and J. -M. Poumirol and C. Barreteau and E. Giannini and D. van der Marel},
journal= {arXiv preprint arXiv:1610.10045},
year = {2016}
}