Competing Vortex Topologies in Iron-Based Superconductors br

In this Letter, we establish a new theoretical paradigm for vortex Majorana physics in the recentlydiscovered topological iron-based superconductors (TFeSCs). While TFeSCs are widely accepted as anexemplar of topological insulators (TIs) with intrinsics-wave superconductivity, our theory implies thatsuch a common belief could be oversimplified. Our main finding is that the normal-state bulk Dirac nodes,usually ignored in TI-based vortex Majorana theories for TFeSCs, will play a key role of determining thevortex state topology. In particular, the interplay between TI and Dirac nodal bands will lead to multiplecompeting topological phases for a superconducting vortex line in TFeSCs, including an unprecedentedhybrid topological vortex state that carries both Majorana bound states and a gapless dispersion.Remarkably, this exotic hybrid vortex phase generally exists in the vortex phase diagram for our minimalmodel for TFeSCs and is directly relevant to TFeSC candidates such as LiFeAs. When the fourfold rotationsymmetry is broken by vortex-line tilting or curving, the hybrid vortex gets topologically trivialized andbecomes Majorana free, which could explain the puzzle of ubiquitous trivial vortices observed in LiFeAs.The origin of the Majorana signal in other TFeSC candidates such as FeTexSe1-xand CaKFe4As4is alsointerpreted within our theory framework. Our theory sheds new light on theoretically understanding andexperimentally engineering Majorana physics in high-temperature iron-based systems