Spin-orbit-coupled ferroelectric superconductivity

TL;DR

This paper explores the coexistence of ferroelectric-like order and superconductivity in a 2D Rashba superconductor, revealing how magnetic fields induce ferroelectric order and how such states can be stable at low carrier densities, paving the way for superconducting multiferroics.

Contribution

It introduces a model for FE-like order in superconductors with Rashba ASOC, showing magnetic field-induced ferroelectricity and stability of FE superconductivity at low carrier densities.

Findings

FE-like order is induced by magnetic field in superconducting state

FE superconductivity can be stable at low carrier densities without magnetic field

Superconducting multiferroics can be realized through control of electric polarization

Abstract

Motivated by recent studies on ferroelectric-like order coexisting with metallicity, we investigate ferroelectric (FE) superconductivity in which a FE-like structural phase transition occurs in the superconducting state. We consider a two-dimensional s-wave superconductor with Rashba-type antisymmetric spin-orbit coupling (ASOC). Assuming linear relationship between polar lattice displacement and strength of the ASOC, we treat the Rashba-type ASOC as a molecular field of FE-like order. It is shown that the FE-like order is induced by the magnetic field when the system is superconducting. Furthermore, we clarify the FE superconductivity in a low carrier density regime, which was recently discovered in doped SrTiO$_3$. It is demonstrated that the FE superconducting state can be stable in this regime in the absence of the magnetic field. Our results open a way to control the electric polarization by superconductivity, that is, superconducting multiferroics.