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

TL;DR

This paper proposes a model where a screw dislocation on the surface of an iron-based superconductor induces a Majorana zero mode by altering boundary conditions, confirmed through numerical simulation and effective theory.

Contribution

It introduces a novel mechanism for Majorana zero mode creation via screw dislocation-induced boundary condition change on superconductor surfaces.

Findings

Screw dislocation transforms boundary conditions, enabling Majorana zero mode formation.

Majorana zero mode persists even as the hole radius approaches zero.

Numerical and effective theory confirm the proposed scenario.

Abstract

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.