Proximity-Induced Superconductivity at Non-Helical Topological Insulator Interfaces

TL;DR

This paper investigates how non-helical spin textures at topological insulator-superconductor interfaces influence proximity-induced superconductivity, revealing symmetry-dependent effects and experimental signatures in conductance measurements.

Contribution

It demonstrates the dependence of induced superconductivity on interface symmetry and spin textures, especially for chiral spin-triplet superconductors, and predicts experimental signatures.

Findings

Nodal superconductivity arises with broken twofold rotational symmetry.

Andreev conductance reveals symmetry-breaking effects at interfaces.

Spin textures influence the nature of proximity-induced superconductivity.

Abstract

We study how non-helical spin textures at the boundary between a topological insulator (TI) and a superconductor (SC) affect the proximity-induced superconductivity of the TI interface state. We consider TIs coupled to both spin-singlet and spin-triplet SCs, and show that for the spin-triplet parent SCs the resulting order parameter induced onto the interface state sensitively depends on the symmetries which are broken at the TI-SC boundary. For chiral spin-triplet parent SCs, we find that nodal proximity-induced superconductivity emerges when there is broken twofold rotational symmetry which forces the spins of the non-helical topological states to tilt away from the interface plane. We furthermore show that the Andreev conductance of lateral heterostructures joining TI-vacuum and TI-SC interfaces yields experimental signatures of the reduced symmetries of the interface states.