Generic Theory for Majorana Zero Modes in 2D Superconductors.

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Topological Superconductivity

Background:

• Non-Abelian Majorana zero modes (MZM) are typically associated with vortex cores in p_{x}+𝒾p_{y} topological superconductors.
• Realization often requires specific conditions like 2D spin-orbit coupled systems with a single Fermi surface and s-wave proximity coupling.

Purpose of the Study:

• To demonstrate that non-Abelian MZMs are not exclusively tied to bulk topology in 2D superconductors.
• To propose a broader framework for the existence of non-Abelian MZMs in both topological and trivial superconductors.
• To identify new experimental avenues for realizing non-Abelian MZMs.

Main Methods:

• Theoretical analysis of 2D systems with multiple Fermi surfaces gapped by superconducting pairings.
• Investigation of MZM existence under conditions of an odd number of superconducting Fermi surfaces with vortices.
• Introduction of an emergent Chern-Simons invariant for MZM protection.

Main Results:

• The existence of non-Abelian MZMs is shown to be independent of the bulk topology of the superconductor.
• At least one MZM is guaranteed to survive in a generic 2D system with multiple Fermi surfaces if an odd number of these surfaces exhibit superconducting vortices.
• A minimal experimental scheme for realizing MZMs in a 2D superconducting Dirac semimetal with trivial bulk topology is proposed.

Conclusions:

• Non-Abelian MZMs can be realized in a more diverse set of superconducting systems than previously thought.
• The protection mechanism for MZMs can stem from an emergent Chern-Simons invariant, irrespective of bulk topology.
• The proposed scheme in superconducting Dirac semimetals offers a promising direction for experimental realization using cold-atom platforms.