Magnon-mediated superconductivity on the surface of a topological insulator

TL;DR

This paper explores how magnetic fluctuations in adjacent magnetic insulators can induce superconductivity on the surface of topological insulators through magnon-mediated interactions, highlighting the potential of antiferromagnetic interfaces for stronger effects.

Contribution

It demonstrates that antiferromagnetic insulators can enhance magnon-mediated superconductivity on topological insulator surfaces, especially with asymmetric coupling and frustration effects.

Findings

Antiferromagnetic insulators induce stronger interactions than ferromagnetic ones.

Asymmetric coupling to sublattices enhances the induced interactions.

Next nearest neighbor frustration further amplifies the effect.

Abstract

We study superconductivity on the surface of a topological insulator, mediated by magnetic fluctuations in an adjacent ferromagnetic or antiferromagnetic insulator. Superconductivity can arise from effective interactions between helical fermions induced by interfacial fermion-magnon interactions. For both ferromagnetic and antiferromagnetic insulators, these fermion-fermion interactions have the correct structure to facilitate pairing between particles located on the same side of the Fermi surface, also known as Amperean pairing. In antiferromagnets, the strength of the induced interactions can be enhanced by coupling the topological insulator asymmetrically to the two sublattices of the antiferromagnet. This effect is further amplified by next nearest neighbor frustration in the antiferromagnetic insulator. The enhancement makes the induced interactions significantly stronger in the antiferromagnetic case, as compared to the ferromagnetic case. These results indicate that an uncompensated antiferromagnetic interface might be a better candidate than a ferromagnetic interface for proximity-induced magnon-mediated superconductivity on the surface of a topological insulator.