Helical Hinge Majorana Modes in Iron-Based Superconductors

Motivated by recent experiments on FeTe1-xSex, we construct an explicit minimal model of an iron-based superconductor with band inversion at the Z point and nontopological bulk s(+/-) pairing. While there has been considerable interest in Majorana zero modes localized at vortices in such systems, we find that our model-without any vortices-intrinsically supports 1D helical Majorana modes localized at the hinges between (001) and (100) or (010) surfaces, suggesting that this is a viable platform for observing higher-order topological superconductivity. We provide a general theory for these hinge modes and discuss their stability and experimental manifestation. Our work indicates the possible experimental observability of hinge Majorana modes in iron-based topological superconductors.