Superconductivity from the Slater mode: Application to KTaO3 heterostructures

TL;DR

This paper investigates the superconductivity in KTaO3 heterostructures, focusing on the role of the Slater mode phonon exchange, and finds that additional phonon contributions are needed to explain the observed transition temperatures.

Contribution

It introduces a theory linking the Slater mode phonon exchange to superconductivity in KTaO3 2DEGs, highlighting the orientation dependence and the need for other phonon contributions.

Findings

Orientation dependence matches experiments

Anisotropic gap function predicted

BCS coupling constant is insufficient alone

Abstract

Superconductivity has been observed for the 2D electron gas (2DEG) at the interface of KTaO3 with other oxides, with a transition temperature about an order of magnitude higher than its 3d cousin SrTiO3. The superconducting transition temperature is strongly dependent on the orientation of the interface. Motivated by this observation, we study pairing due to exchange of the soft transverse optic phonon mode characteristic of quantum paraelectrics and use the resulting theory to comment on the nature of superconductivity of this 2DEG. We find (1) an orientation dependence consistent with experiment along with an anisotropic gap function, but (2) a BCS coupling constant that is smaller than needed and so must be augmented by contributions from other phonons to be consistent with the observed values of Tc.