Majorana Zero Mode Induced by a Screw Dislocation on the Surface of an Iron-based Superconductor

We propose a simple scenario to describe a dislocation-induced Majorana zero mode on the surface of an iron-based superconductor, using an illustrative model with a cylindrical hole of radius $R$ perpendicular to its top surface. Topological surface states on the inner surface of the hole form an effective chiral $p$-wave superconductor. When the top surface has a perpendicular magnetization, chiral Majorana modes appear near the circular edge of the hole. Since the corresponding wavefunctions obey an antiperiodic boundary condition in the circumferential direction, a Majorana zero mode at zero energy does not appear. However, if a screw dislocation is inserted through the hole, the antiperiodic boundary condition is transformed into a periodic one, resulting in the appearance of a Majorana zero mode. This Majorana zero mode remains in the no-hole limit of $R \to 0$. We confirm this scenario by numerical simulation and effective theory. A method of creating a Majorana zero mode in the absence of the surface magnetization is briefly described.