Majorana Flat Bands in s-Wave Gapless Topological Superconductors

Abstract

We demonstrate how the non-trivial interplay between spin-orbit coupling and nodeless $s$-wave superconductivity can drive a fully gapped two-band topological insulator into a time-reversal invariant gapless topological superconductor supporting symmetry-protected Majorana flat bands. We characterize topological phase diagrams by a ${\mathbb{Z}}_2\times {\mathbb{Z}}_2$ partial Berry-phase invariant, and show that, despite the trivial crystal geometry, no unique bulk-boundary correspondence exists. We trace this behavior to the anisotropic quasiparticle bulk gap closing, linear vs. quadratic, and argue that this provides a unifying principle for gapless topological superconductivity. Experimental implications for tunneling conductance measurements are addressed, relevant for lead chalcogenide materials.

5 pages, 4 figures, Phys. Rev. B, Rapid Comm. published version

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• Magnetic Field Driven Nodal Topological Superconductivity in Monolayer Transition Metal Dichalcogenides
• Majorana bound states in open quasi-1D and 2D systems with transverse Rashba coupling
• Exact Solution of Quadratic Fermionic Hamiltonians for Arbitrary Boundary Conditions
• Flat Majorana bands in 2-d lattices with inhomogeneous magnetic fields: topology and stability
• Squaring the fermion: The threefold way and the fate of zero modes
• Generalization of Bloch's theorem for arbitrary boundary conditions: Interfaces and topological surface band structure
• On the bulk boundary correspondence and the existence of Majorana bound states on the edges of 2D topological superconductors
• Gapless Topological Superconductors - Model Hamiltonian and Realization
• Rashba Sandwiches with Topological Superconducting Phases
• Flat bands and entanglement in the Kitaev ladder
• Dynamical generation of Floquet Majorana flat bands in s-wave superconductors
• Majorana fermions in finite-size strips with in-plane magnetic fields
• Stability of flat zero-energy states at the dirty surface of a nodal superconductor
• Type-I and type-II topological nodal superconductors with $s$-wave interaction
• Symmetry conditions of a nodal superconductor for generating robust flat-band Andreev bound states at its dirty surface
• Floquet Graphene Antidot Lattices
• Nodal Nematic Superconductivity in Multiple-Flat-Band Land
• Andreev spectroscopy of Majorana states in topological superconductors with multipocket Fermi surfaces
• Topological transitions in two-dimensional Floquet superconductors
• Quantized Thermal Hall Conductance and the Topological Phase Diagram of a Superconducting Bismuth Bilayer
• Boundary Flat Bands with Topological Spin Textures Protected by Sub-chiral Symmetry
• A theorem regarding families of topologically non-trivial fermionic systems