Andreev spectroscopy of nonhelical spin textures in topological insulators

TL;DR

This paper investigates how nonhelical spin textures influence superconductivity at topological insulator-superconductor interfaces, revealing that conductance signatures depend on specific spin textures and superconductor types.

Contribution

It introduces a detailed analysis of conductance in TI-SC heterojunctions considering nonhelical spin textures and interface mismatches, extending understanding of proximity effects in topological materials.

Findings

Nonhelical spin textures cause specific conductance signatures in TI-SC interfaces.

Conductance depends on the type of superconductor and spin texture mismatch.

Nonzero conductance signatures are only present for certain spin textures with spin-triplet SCs.

Abstract

We study how nonhelical spin textures affect the proximity-induced superconductivity of topological insulator (TI)-superconductor (SC) interface states. In particular we calculate the conductance of lateral heterojunctions which comprise a TI surface that is only partially covered by a superconducting material. Interface potentials at the TI-SC interface may lead to a Fermi velocity and spin texture mismatch between the two regions of the lateral heterojunction. By enforcing the hermiticity of the total Hamiltonian, we derive the boundary conditions and calculate the conductance of the structure in both the normal and superconducting state. The total Andreev conductance is calculated for both $s$-wave and spin-triplet parent SCs, and for several examples of nonhelical spin textures which lead to different Fermi surface mismatches between the two planar regions of the heterojunction. We find that for spin-triplet SCs, nonzero conductance signatures only appear for certain combinations of nonhelical spin textures and parent superconducting material.