Robustness of Majorana fermions in proximity-induced superconductors

In two-dimensional chiral p-wave superconductors, the zero-energy Majorana fermion excitations trapped at vortex cores are protected from the thermal effects by the minigap, Delta(2)/epsilon(F) (Delta : bulk gap, epsilon(F): Fermi energy), which is the excitation gap to the higher energy bound states in the vortex cores. Robustness to thermal effects is guaranteed only when T <<Delta 2/epsilon F similar to 0.1 mK, which is a very severe experimental constraint. Here we show that when s-wave superconductivity is proximity-induced on the surface of a topological insulator or a spin-orbit-coupled semiconductor, as has been recently suggested, the minigaps of the resultant non-Abelian states can be orders of magnitude larger than in a chiral p-wave superconductor. Specifically, for interfaces with sufficient barrier transparencies, the minigap can be as high as similar to Delta >>Delta(2)/epsilon(F), where Delta is the bulk gap of the s-wave superconductor.