Andreev spectroscopy of nonhelical spin textures in topological insulators

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 conservation of current across the interface, we derive the boundary conditions and calculate the conductance 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.

Automated summary

We study the influence of nonhelical spin textures on the proximity-induced superconductivity in the interface states of topological insulator-superconductor heterojunctions. By calculating the conductance of lateral heterojunctions, we find that interface potentials may cause a mismatch in Fermi velocity and spin texture between the two regions. By enforcing current conservation across the interface, we derive boundary conditions and calculate the conductance in both normal and superconducting states. We find that nonzero conductance signatures only appear for certain combinations of nonhelical spin textures and parent superconducting materials in the case of spin-triplet superconductors.