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

Abstract

We use first-principles methods to study doped strong ferroelectrics (taking BaTiO3 as a prototype). Here, we find a strong coupling between itinerant electrons and soft polar phonons in doped BaTiO3, 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 BaTiO3, 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 BaTiO3 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.

Superconducting dome in ferroelectric-type materials from soft mode instability

“…both above and below n c ; or in other words, both in the ferroelectric and in the paraelectric phase. A physical explanation for this widely observed behavior 10,14,15 is thus offered by the structure of our model. The mechanism giving rise to the T c trend in Fig.…”

“…In all the relevant experimental systems 10,14,15,34 the anharmonic phonon damping plays a key role 24 , which is reflected in gigantic values of the Grüneisen parameter as recently observed in Ref. 15 .…”

“…52 . In ferroelectric-type SCs, n could be electron doping 14 or the mechanical strain 15 , n ≡ . In both cases, the variation of the control parameter n changes the phonon damping Γ, as mentioned above.…”

“…Even though the unusual conditions due to extreme dilution of electrons make the pairing mechanism in SrTiO 3 still a highly debated topic, a basic BCS framework can be applied to extract qualitative pairing trends. 12,13 More recently, enhanced superconductivity domes in the proximity of soft mode instabilities, induced by electron doping 14 and mechanical strain 15 , have been observed. The role of structural instability in promoting superconductivity is suggested by the recent finding that plastic mechanical deformations appear to further enhance superconductivity possibly due to selforganized dislocation networks 16 .…”

Superconductivity from energy fluctuations in dilute quantum critical polar metals

“…Several theories have been advanced to explain superconductivity in polar metals using conventional electronphonon interaction [8] and its extension to include plasmon effects [9][10][11][12][13][14]. Alternative phonon coupling mechanisms requiring spin-orbit coupling or multiband effects [15][16][17][18] have also been examined.…”