Superconductivity mediated by soft polar modes

SrTiO₃ is a material with an ability to store electric energy that grows to be exceptionally strong at low temperatures. This surprising anomaly is explained by a tendency to form a ferroelectric, a state in which an electric polarization would spontaneously develop but does not. Equally surprising, more than 50 years ago, it was discovered that SrTiO₃ becomes superconducting at extremely low densities of chemically introduced electrons. This has defied established theories of superconductivity, which assume much larger electronic densities as a starting point.

During this project the student will study the mechanism for superconductivity that arises from the coupling of electrons to a pair of soft polar modes. This involves constructing the effective electron-electron interaction, analyzing its structure, and solving the resulting pairing problem considering both the dynamics and momentum structure. The results obtained by the student during this internship will shed light into the largely unexplored link between the ferroelectric and superconducting phases of matter.