Helical Hinge Majorana Modes in Iron-Based Superconductors

Abstract

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 non-topological 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 Majoranas in iron-based topological superconductors.arXiv:1812.10493v2 [cond-mat.supr-con]

On the Remarkable Superconductivity of FeSe and Its Close Cousins

“…Another possibility for generating 1D helical Majorana modes in FeTe 0.55 Se 0.45 was first discussed theoretically by Zhang et al [429], who predicted the emergence of so-called higher-order superconducting topology with associated 1D localized helical Majorana hinge states between (001) and (100) or (010) surfaces. An n'th order topological phase hosted in a D-dimensional system features (D − n)-dimensional topological edge states [430][431][432][433].…”

Trails of Mobile Majoranas in an Iron Chalcogenide?

“…It is claimed that this ZBCP is the evidence of a recent theoretical proposal of "helical hinge Majorana fermions" [9]. This theory [9] proposed that superconductors with unconventional s pm pairing and topological surface states are "higher-order topological superconductors", with symmetry-protected helical Majorana fermions on the hinges between (001) and (100) surfaces. The basic idea is that the bulk s pm pairing may induce pairing order parameters with opposite signs on the two surfaces, and the hinge line between the two surfaces become a "π-phase shift domain wall" (see Fig.…”

FeTe0.55Se0.45 van der Waals tunneling devices

“…Furthermore, the symmetry of the superconducting order parameter is as yet unsettled, with evidence in favor of S ± symmetry [11]. The unconventional S ± symmetry in a topological superconductor has been suggested to give rise to chiral one-dimensional "hinge" modes at the intersection between two faces of the superconductor [12,13].…”