Emergence of Superconductivity Around Polar Quantum Critical Point in Doped Ferroelectrics

We combine first-principles calculations and Eliashberg equation to demonstrate that with itinerant electrons inducing a polar-to-centrosymmetric quantum critical point (pQCP) in doped ferroelectrics, softened zone-center polar phonon modes strongly couple to itinerant electrons, which enhances electron-phonon coupling around pQCP. By considering a prototypical ferroelectric material BaTiO3, we find that around its pQCP, electron-phonon coupling is increased to about 0.5, sufficiently large to induce phonon-mediated superconductivity with an optimal transition temperature of about 1 K. However, different from superconducting dome associated with other structural quantum critical points, around pQCP the superconducting transition temperature of doped BaTiO3 is enhanced much more substantially in the polar phase than in the cubic phase.