Surface step states and Majorana end states in profiled topological insulator thin films

Abstract

The protected helical surface states in thin films of topological insulators (TI) are subject to inter-surface hybridisation. This leads to gap opening and spin texture changes as witnessed in photoemission and quasiparticle interference investigations. Theoretical studies show that universally the hybridisation energy exhibits exponential decay as well as sign oscillations as a function of film thickness, depending on the effective band parameters of the material. When a step is introduced in the TI film e.g. by profiling the substrate such that the hybridisation has different signs on both sides of the step, 1D bound states appear within the hybridisation gap which decay exponentially with distance from the step. The step bound states have linear dispersion and inherit the helical spin locking from the surface states and are therefore non-degenerate. When the substrate becomes an s-wave superconductor Majorana zero modes located at the step ends are created inside the superconducting gap. The proposed scenario involves just a suitably stepped interface of superconductor and TI and therefore may be a most simple device being able to host Majorana zero modes.

10 pages, 5 figures

References in corpus (9)

• Evidence of Majorana fermions in an Al - InAs nanowire topological superconductor
• Topological Surface States Protected From Backscattering by Chiral Spin Texture
• Colloquium: Majorana Fermions in nuclear, particle and solid-state physics
• Non-Abelian quantum order in spin-orbit-coupled semiconductors: The search for topological Majorana particles in solid state systems
• Distinguishing a Majorana zero mode using spin resolved measurements
• Intrinsic conduction through topological surface states of insulating Bi${}_2$Te${}_3$ epitaxial thin films
• Stability of Majorana Fermions in Proximity-Coupled Topological Insulator Nanowires
• Majorana bound states in semiconducting nanostructures
• Spin-orbit scattering visualized in quasiparticle interference