A large modulation of electron-phonon coupling and an emergent superconducting dome in doped strong ferroelectrics

TL;DR

This study reveals a significant modulation of electron-phonon coupling in doped BaTiO₃, leading to superconductivity, and challenges the traditional weak coupling view in ferroelectric-like metals.

Contribution

It demonstrates strong electron-phonon coupling and superconductivity in doped BaTiO₃, showing a new pathway to induce superconductivity in strong ferroelectrics.

Findings

Electron-phonon coupling increases to ~0.6 at the phase transition.

Superconductivity of about 2 K is induced by doping.

Epitaxial strain can further enhance superconducting temperature.

Abstract

We use first-principles methods to study doped strong ferroelectrics (taking BaTiO$_3$ as a prototype). Here we find a strong coupling between itinerant electrons and soft polar phonons in doped BaTiO$_3$, contrary to Anderson/Blount's weakly coupled electron mechanism for "ferroelectric-like metals". As a consequence, across a polar-to-centrosymmetric phase transition in doped BaTiO$_3$, the total electron-phonon coupling is increased to about 0.6 around the critical concentration, which is sufficient to induce phonon-mediated superconductivity of about 2 K. Lowering the crystal symmetry of doped BaTiO$_3$ by imposing epitaxial strain can further increase the superconducting temperature via a sizable coupling between itinerant electrons and acoustic phonons. Our work demonstrates a viable approach to modulating electron-phonon coupling and inducing phonon-mediated superconductivity in doped strong ferroelectrics and potentially in polar metals. Our results also show that the weakly coupled electron mechanism for "ferroelectric-like metals" is not necessarily present in doped strong ferroelectrics.