Isotope tuning of the superconducting dome of strontium titanate

Doped strontium titanate SrTiO_{3} (STO) is one of the most dilute superconductors known today. The fact that superconductivity occurs at very low carrier concentrations is one of the two reasons that the pairing mechanism is not yet understood, the other being the role played by the proximity to a ferroelectric instability. In undoped STO, ferroelectric order can in fact be stabilized by substituting ^{16}O with its heavier isotope ^{18}O. Here, we explore the superconducting properties of doped and isotope-substituted SrTi(^{18}O_{y}^{16}O_{1−y})_{3−δ} for 0≤y≤0.81 and carrier concentrations between 6×10^{17} and 2×10^{20}cm^{−3} (δ