Isotope tuning of the superconducting dome of strontium titanate

Abstract

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 is 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${}_{1-y}{)}_{3-\delta }$ for $0\le y\le 0.81$ and carrier concentrations between $6\times 10^{17}$ and $2\times 10^{20}$ cm${}^{-3}$ ($\delta <0.02$). We show that the superconducting $T_c$ increases when the ${}^{18}$O concentration is increased. For carrier concentrations around $5\times 10^{19}$~cm${}^{-3}$ this $T_c$ increase amounts to almost a factor $3$, with $T_c$ as high as 580~mK for $y=0.74$. When approaching SrTi${}^{18}$O${}_3$ the maximum $T_c$ occurs at a much smaller carrier densities than for pure SrTi${}^{16}$O${}_3$. Our observations agree qualitatively with a scenario where superconducting pairing is mediated by fluctuations of the ferroelectric soft mode.

arXiv comment8 pages, 11 figures

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Cited by in corpus (10)

• Phonon drag thermal Hall effect in metallic strontium titanate
• Superconductivity enhancement in polar metal regions of Sr${}_{0.95}$Ba${}_{0.05}$TiO${}_3$ and Sr${}_{0.985}$Ca${}_{0.015}$TiO${}_3$ revealed by the systematic Nb doping
• Generalized Rashba Electron-Phonon Coupling and Superconductivity in Strontium Titanate
• Effects of spin-orbit interaction and electron correlations in strontium titanate
• Anisotropic resistivity and superconducting instability in ferroelectric metals
• Modeling polar order in compressively strained SrTiO${}_3$
• Effects of Homogeneous Doping on Electron-Phonon Coupling in SrTiO3
• Spin-dependent anisotropic electron-phonon coupling in KTaO${}_3$
• Phonon-mediated spin transport in quantum paraelectric metals
• Effects of doping on polar order in SrTiO${}_3$ from first-principles modeling