Competing Vortex Topologies in Iron-Based Superconductors.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Physics

Background:

• Topological iron-based superconductors (TFeSCs) are typically viewed as topological insulators with superconductivity.
• Existing theories for vortex Majorana physics in TFeSCs often overlook the role of normal-state bulk Dirac nodes.

Purpose of the Study:

• To establish a new theoretical framework for understanding vortex Majorana physics in TFeSCs.
• To investigate the influence of normal-state Dirac nodes on the topological properties of superconducting vortices.

Main Methods:

• Development of a new theoretical paradigm for vortex Majorana physics.
• Analysis of the interplay between topological insulator and Dirac nodal bands in TFeSCs.
• Construction of a minimal model for TFeSCs, including candidates like LiFeAs.

Main Results:

• Normal-state bulk Dirac nodes are crucial in determining vortex state topology.
• A novel hybrid topological vortex state, featuring Majorana bound states and gapless dispersion, is predicted.
• This hybrid state can become trivial (Majorana-free) when rotational symmetry is broken, explaining experimental observations in LiFeAs.

Conclusions:

• The proposed theory offers a more comprehensive understanding of vortex Majorana physics in TFeSCs.
• It provides a unified framework to interpret Majorana signals in various TFeSC candidates.
• The findings pave the way for experimental engineering of Majorana physics in high-temperature iron-based systems.