Ferroelectricity, quantum paraelectricity and superconductivity

Ferroelectricity and superconductivity are two fascinating and well studied materials phenomena by themselves, but there are certain materials in which both properties coexist. We have computationally shown that ferroelectricity in BaTiO₃ unexpectedly persists even if free carriers are introduced, with different behavior depending on the actual dopant. [1] Related to that, a so-called quantum paraelectric state exists in the two perovskite materials SrTiO₃ and KTaO₃ at low temperature, and superconductivity appears as well below 2K. Using density functional theory and additional methods, we are studying this quantum paraelectric state in detail, with the two aims of understanding it fundamentally, and finding out if it is related to the superconducting state, and if so, how.

Figure 1: Polarization of tetragonal (black) and cubic (grey) BaTiO₃ with hole- and electron-doping and corresponding charge carrier distribution inside the unit cell (shown as isosurfaces).

Reference

V. F. Michel, T. Esswein, and N. A. Spaldin, external pageInterplay between ferroelectricity and metallicity in BaTiO₃, J. Mater. Chem. C, vol. 9, no. 27, pp. 8640–8649 (2021).