Bound-state spectrum of superconductors with magnetic-texture defects

Recent experiments [1] provided evidence for zero-energy Majorana bound states (MBSs) when magnetic adatoms are deposited onto a superconductor. Such observations are reconcilable by means of 0D-like defects which trap MBSs. Existing explanations rely on the presence of isolated magnetic skyrmions or vortices in the spin-orbit coupling field. These need to be contrasted to the standard mechanism, in which MBSs are trapped in vortices of the superconducting order parameter. Inspired from the above, we explore a novel promising path towards realizing MBSs, which relies on 0D defects in the order parameter describing a textured magnetic order that coexists with spin-singlet superconductivity. This scenario appears relevant for iron-pnictides, where a theoretical study [2] has revealed that textured magnetism is accessible in doped BaFe₂As₂ and LaFeAsO. Here, we perform a thorough numerical investigation of the bound-state energy spectrum arising when vortices are introduced in the order parameter of spin-spiral and -whirl magnetic orders. Our preliminary results indicate that the defect-induced MBSs are accessible in superconductors which yield a nodal spectrum in the absence of the magnetic order.

[1] Ménard et al, Nat. Com. 10, 2587 (2019)
[2] Christensen et al, PRX 8, 041022 (2018)