A possible mechanism for superconductivity in doped SrTiO3

Abstract

The soft ferro-electric phonon in SrTiO3 observed with optical spectroscopy has an extraordinary strong spectral weight which is much stronger than expected in the limit of a perfectly ionic compound. The "charged phonon" in SrTiO3 is caused by the close-to-covalent character of the Ti-O ionic bond and implies a strong coupling between the soft ferro-electric phonon and the inter band transitions across the 3 eV gap of SrTiO3. We demonstrate that this coupling leads, in addition to the charged phonon effect, to a pairing interaction involving the exchange of two transverse optical phonons. This process owes its relevance to the strong electron-phonon coupling and to the fact that the interaction mediated by a single transverse optical phonon vanishes at low electron density. We use the experimental soft phonon spectral weight to calculate the strength of the bi-phonon mediated pairing interaction in the electron doped material and show that it is of the correct magnitude when compared to the experimental value of the superconducting critical temperature.

arXiv commentMissing factors corrected in Eqs. 6 and 7

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• Orientation-dependent electron-phonon coupling in interfacial superconductors LaAlO3/KTaO3
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• 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
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• Generalized Rashba Electron-Phonon Coupling and Superconductivity in Strontium Titanate
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• Polaron with Quadratic Electron-phonon Interaction
• Multiband Quantum Criticality of Polar Metals
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• Synergetic ferroelectricity and superconductivity in zero-density Dirac semimetals near quantum criticality
• "Quantum bipolaron" superconductivity from quadratic electron-phonon coupling
• Giant Grüneisen parameter in a strain-tuned superconducting quantum paraelectric: A consequence of the vanishing ferroelectric phonon energy
• Floquet engineering of many-body states by the ponderomotive potential
• Soliton States From Quadratic Electron-Phonon Interaction
• Anisotropic resistivity and superconducting instability in ferroelectric metals
• Precision measurements of the AC field dependence of the superconducting transition in strontium titanate
• Emergent superconductivity in doped ferroelectric hafnia
• Ferroelectricity-induced multiorbital odd-frequency superconductivity in SrTiO${}_3$
• A local maximum in the superconducting transition temperature of Nb-doped strontium titanate under uniaxial compressive stress
• Optical conductivity of an anharmonic large polaron gas at weak coupling
• Analytic method for quadratic polarons in nonparabolic bands
• Modeling polar order in compressively strained SrTiO${}_3$
• Soft phonon and the central peak at the cubic-to-tetragonal phase transition in SrTiO${}_3$
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• Strain-engineered interaction of quantum polar and superconducting phases
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• Superconductivity from the Slater mode: Application to KTaO3 heterostructures
• Spin-dependent anisotropic electron-phonon coupling in KTaO${}_3$
• A large modulation of electron-phonon coupling and an emergent superconducting dome in doped strong ferroelectrics
• Effects of doping on polar order in SrTiO${}_3$ from first-principles modeling
• Stability conditions for a large anharmonic bipolaron