Superconductivity in the vicinity of a ferroelectric quantum phase transition

Abstract

Superconductivity has been observed in doped SrTiO${}_3$ at charge-carrier densities below 10${}^{18}$ cm${}^{-3}$, where the density of states at the Fermi level of the itinerant electrons is several orders of magnitude lower than that of conventional metals. In terms of the Bardeen-Cooper-Schrieffer description, this implies the existence of an extraordinarily strong interaction driving the formation of Cooper pairs, potentially comparable in order of magnitude to that in some high Tc superconductors. Under suitable conditions the interaction might remain effective at densities approaching metallic densities, leading to the possibility of pair formation at elevated temperatures. Here we investigate the pressure dependence of the resistivity and superconducting transition temperature, Tc, of SrTiO${}_3$ at a carrier density near to optimal doping. Our experiments show that Tc collapses rapidly with pressure and hence with increasing frequency of the soft transverse-optical phonon mode connected to the ferroelectric quantum critical point. We show that the superconductivity phase diagram can be understood in terms of the coupling of electrons via two hybrid longitudinal polar modes, based on a model of dipolar fluctuations of the charge carrier-ion system. In particular, we predict that for carrier densities above the order of 10${}^{18}$ cm${}^{-3}$, Tc can be strongly enhanced on approaching the ferroelectric quantum critical point, as seen in our measurements of SrTiO${}_3$ and as found in many electrically conducting magnetic analogues. However below this density we predict the reverse behaviour, namely that Tc is suppressed on approaching the ferroelectric quantum critical point. Our model is also relevant to superconductivity found in gated ferroelectric quantum critical systems such as KTaO${}_3$ and can guide searches for new superconductors in a diversity of materials.

References in corpus (17)

• Quantum criticality in ferroelectrics
• Electron-phonon interaction and charge carrier mass enhancement in SrTiO3
• Quantum critical origin of the superconducting dome in SrTiO${}_3$
• Critical doping for the onset of a two-band superconducting ground state in SrTiO${}_{3-\delta }$
• Fermi surface of the most dilute superconductor
• Superconductivity at very low density: the case of strontium titanate
• Phonon mechanism in the most dilute superconductor: n-type SrTiO3
• Superconductivity vs bound state formation in a two-band superconductor with small Fermi energy -- applications to Fe-pnictides/chalcogenides and doped SrTiO3
• Prospects and Applications Near Ferroelectric Quantum Phase Transitions
• Dynamics of relaxor ferroelectrics
• Two-band superconductivity in doped SrTiO${}_3$ films and interfaces
• Metallicity without quasi-particles in room-temperature strontium titanate
• Quantum Critical Paraelectrics and the Casimir Effect in Time
• Charge transfer and electron-phonon coupling in monolayer FeSe on Nb doped SrTiO${}_3$
• Pairing from dynamically screened Coulomb repulsion in bismuth
• Paraelectric and Ferroelectric States in a Model for Relaxor Ferroelectrics
• Structure Factor of a Relaxor Ferroelectric

Cited by in corpus (8)

• Metallicity and superconductivity in doped strontium titanate
• Anisotropic superconductivity mediated by ferroelectric fluctuations in cubic systems with spin-orbit coupling
• Charge Transport in a Polar Metal
• Quantum Critical Phenomena in a Compressible Displacive Ferroelectric
• Implicit renormalization approach to the problem of Cooper instability
• Kohn-Luttinger Correction to Tc in a Phonon Superconductor
• A local maximum in the superconducting transition temperature of Nb-doped strontium titanate under uniaxial compressive stress
• Modeling polar order in compressively strained SrTiO${}_3$