Intertwined Charge Stripes and Majorana Zero Modes in An Iron-Based Superconductor

TL;DR

This study uncovers intertwined charge-stripe order and Majorana zero modes within magnetic vortices in an iron-based superconductor, revealing complex vortex phenomena and novel quantum states linked to density-wave textures.

Contribution

It demonstrates the coexistence of charge-stripe order with Majorana modes and vortex types in an iron-based superconductor, a novel observation in this material class.

Findings

Charge-stripe order nucleates inside vortices and extends into the vortex halo.

Charge order modulates Andreev bound states, leading to distinct vortex quantizations.

Presence of Majorana zero modes in non-abelian vortices within the superconductor.

Abstract

In type-II superconductors, magnetic fields modulate the amplitude and phase of the superconducting order parameter, forming quantized vortices where superconductivity is locally suppressed and exotic bound states or competing electronic orders emerge. Using spectroscopic-imaging scanning tunneling microscopy on epitaxial Ba(Fe$_{0.94}Co$_{0.06})$_2$As$_2$ films, we discover an incommensurate charge-stripe order aligned with the Fe-Fe bond direction and nucleated inside magnetic vortices. These charge modulations intensify at the vortex core, extend far into the vortex halo, and persist within the superconducting gap. Strikingly, the charge order modulates Andreev bound states of vortices at non-zero energies, producing abelian vortices with half-odd-integer level quantization and non-abelian vortices with integer-quantized core states that host a Majorana zero mode. The distinct vortex types are distinguished by the registry of their centers relative to the charge-stripe pattern and remain robust in ultrathin (2.5-unit-cell) films. Our findings reveal a density-wave-textured vortex matter and provide fresh insights into the intertwined phenomena of charge-stripe order, pair-density-wave modulations, and Majorana physics in iron-based superconductors.