films

We report on the superconducting characteristics of doped 180-nm-thick SrTiO₃ films, grown by molecular beam epitaxy on (001) LSAT substrates. The epitaxial compressive strain induced by the substrate stabilizes a ferroelectric phase in the SrTiO₃ for carrier concentrations ranging from 5×10¹⁹ – 1.5×10²⁰ cm^-3 [1,2]. A systematic study of the critical temperature and critical field as a function of the carrier density and type of doping atom reveal deviations from those expected for a single-band BCS superconductor. In particular, the critical temperature and critical field show qualitative different evolutions, with the latter exceeding the Pauli limit for certain values. We discuss the role of the band structure and inversion symmetry breaking.

[1] K. Ahadi, et al., Sci. Adv. 5, eaaw0120 (2019).
[2] R. Russell, et al., Phys. Rev. Mater. 3, 091401(R) (2019).