Metallization and proximity superconductivity in topological insulator nanowires

A heterostructure consisting of a topological insulator (TI) nanowire brought into proximity with superconducting layer provides promising route to achieve superconductivity and associated Majorana bound states (MBSs). Here, we study effects caused by such coupling between thin an $s$-wave superconductor TI nanowire. We show that there is distinct phenomenology arising from the metallization in superconductor. In strong limit, required induce large pairing potential, find results shift subbands ($\sim 20$ meV) as well it leads small reduction size subband gap opened magnetic field applied parallel axis. Surprisingly, nanowires can also be beneficial. Most notably, induces potential portion close interface superconductor, this breaks inversion symmetry at finite momentum lifts spin degeneracy within subband. As create or enhance splitting key achieving superconductivity. This stark contrast semiconductors, where has been shown always reduce equivalent subband-splitting spin-orbit coupling. certain geometries critical enter phase. conclude that, unlike occur relatively easily mitigated, for instance modifying geometry attached compensation material.