Superconductive proximity in a Topological Insulator slab and excitations bound to an axial vortex

Abstract

We consider the proximity effect in a Topological Insulator sandwiched between two conventional superconductors, by comparing s-wave spin singlet superconducting pairing correlations and odd-parity triplet pairing correlations with zero spin component orthogonal to the slab ("polar " phase). A superconducting gap opens in the Dirac dispersion of the surface states existing at the interfaces. An axial vortex is included, piercing the slab along the normal to the interfaces with the superconductors. It is known that, when proximity is s-wave, quasiparticles in the gap are Majorana Bound States, localized at opposite interfaces. We report the full expression for the quantum field associated to the midgap neutral fermions, as derived in the two-orbital band model for the TI. When proximity involves odd-parity pairing, midgap modes are charged Surface Andreev Bound States, and they originate from interfacial circular states of definite chirality, centered at the vortex singularity and decaying in the TI film with oscillations. When the chemical potential is moved away from midgap, extended states along the vortex axis are also allowed. Their orbital structure depends on the symmetry of the bulk band from where the quasiparticle level splits off.

13 pages no figures, accepted for publication in Phys. Rev. B

References in corpus (8)

• Superconducting proximity effect and Majorana fermions at the surface of a topological insulator
• Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface
• Classification of topological insulators and superconductors in three spatial dimensions
• First direct observation of Spin-textures in Topological Insulators : Spin-resolved ARPES as a probe of topological quantum spin Hall effect and Berry's phase
• Topological Defects and Gapless Modes in Insulators and Superconductors
• Supercurrent blockade in Josephson junctions with a Majorana wire
• Spin connection and boundary states in a topological insulator
• Majorana zero modes bound to a vortex line in a topological superconductor

Cited by in corpus (1)

• $Z_2$ index for gapless fermionic modes in the vortex core of three dimensional paired Dirac fermions