Double Majorana Vortex Flat Bands in the Topological Dirac Superconductor

TL;DR

This paper explores vortex-bound states in superconducting Dirac semimetals, revealing robust double Majorana vortex flat bands protected by topology and symmetry, with implications for experimental detection in correlated materials.

Contribution

It uncovers the existence of double Majorana vortex flat bands in Dirac semimetals with unconventional pairing, a novel topological feature not previously studied in such systems.

Findings

Double Majorana vortex flat bands are identified at zero energy.

Flat bands are protected by a nontrivial $ ext{Z}_2$ topology and four-fold rotational symmetry.

The study discusses experimental implications for correlated Dirac semimetals like iron-based superconductors.

Abstract

Vortex lines, known as topological defects, are cable of trapping Majorana modes in superconducting topological materials. Previous studies have primarily focused on topological bands with conventional s-wave pairing. However, topological Dirac semimetals exhibiting a unique orbital texture can favor unconventional pairing when electronic correlations are significant. The topology of vortices in these systems has yet to be explored. In this work, we investigate the vortex bound states in superconducting Dirac semimetals, with a particular focus on the orbital-singlet unconventional pairing, which generates higher-order Majorana hinge modes. Remarkably, we identify robust double Majorana vortex flat bands at zero energy. In type-I Dirac semimetals, these Majorana flat bands are located between the projections of two superconduting Dirac points. In contrast, in type-II Dirac semimetals, they extend across the entire 1D Brillouin zone. These double flat bands arise from a nontrivial $\mathbb{Z}_2$ topology defined by an effective particle-hole symmetry and are protected by the four-fold rotational symmetry. Additionally, we observe that moving the vortex line close to a hinge can trivialize the higher-order Majorana arc on the hinge, leaving a single Majorana mode at the vortex core due to the hybridization of Majorana modes. Finally, we discuss the potential experimental implications for correlated Dirac semimetals, such as electron-doped iron-based superconductors.