Superconductivity at low doping: New pairing mechanism driven by critical ferroelectric modes

Abstract: Superconductivity at low doping is a long-standing enigma. The standard theoretical framework, BCS theory and its extensions, cannot be applied to this regime, but nonetheless, the phenomenon was observed experimentally. I will present a new electrons pairing mechanism, mediated by ferroelectric modes, that is valid in this regime. The transition between para- and ferroelectricity, at zero temperature, is related to a quantum critical point, and this give unique characteristics to the spectrum of the modes, creating a so-called soft mode. The result is analytical solutions for the superconducting order parameter, with peculiar properties related to the quantum critical nature of the pairing. The state would yield unusual experimental observations: (i) A gap function that is non-monotonic in temperature (ii) Superconductivity occurring in an insulator.

Reference: YK, PRB 98 (22), 220505