Ferroelectric superconductivity in noncentrosymmetric metals

Abstract

It has recently been shown in experiments that certain materials can display both superconductivity and ferroelectricity, contrary to a long-standing conjecture that these two phenomena are incompatible, or at least unrelated. In this work we study superconductivity in ferroelectric metals, using a formalism of ionic polarization fields coupled to itinerant electrons, both of which are treated at the microscopic level. The ferroelectric order manifests as a spontaneous polarization that may be uniform or spatially modulated, and fluctuations of the polarization mediate interactions between the electrons. The polarization fluctuations give rise to attractive interactions that can lead to Cooper pairing in certain lattice configurations, analogous to the nonpolar phonons in conventional BCS theory. Working with a simplified BCS model, we derive conditions under which superconductivity can coexist with and even emerge from ferroelectricity.