Single-band superconductivity in low density SrTiO₃

Bulk strontium titanate is a well-known low density multi-band superconductor. Recently, it was found that superconductivity persists to an order of magnitude lower doping (≤10¹⁸ cm^-3). Superconductivity in the low density single-band regime is interesting because the nominal Debye energy is comparable to or greater than the Fermi energy, also known as the non-adiabatic limit. We present a study that combines standard magneto-transport, measurements of Shubnikov de Haas oscillations and superconducting properties to better understand superconductivity in the very low density limit in high mobility reduced single crystals of SrTiO₃.