Electrically controllable spin filtering based on superconducting helical states

TL;DR

This paper develops a microscopic theory for S/3D TI bilayers showing they can act as electrically controllable spin filters due to strong magnetoelectric effects from spin-momentum locking.

Contribution

It introduces a formalism for S/3D TI bilayers and demonstrates their potential as non-magnetic, electrically tunable spin filters based on giant magnetoelectric effects.

Findings

Giant magnetoelectric behavior in the DOS of S/3D TI bilayers

Equal amplitudes of odd-frequency singlet and triplet components due to spin-momentum locking

Connection between odd-frequency pairing and magnetoelectric effects

Abstract

The magnetoelectric effects in the surface states of the 3D TI are extremely strong due to the full spin-momentum locking. Here the microscopic theory of S/3D TI bilayer structures in terms of quasiclassical Green's functions is developed. On the basis of the developed formalism it is shown that the DOS in the S/TI bilayer manifests giant magnetoelectric behavior and, as a result, S/3D TI heterostructures can work as non-magnetic fully electrically controllable spin filters. It is shown that due to the full spin-momentum locking the amplitudes of the odd-frequency singlet and triplet components of the consensate wave function are equal. The same is valid for the even frequency singlet and triplet components. We unveil the connection between the odd-frequency pairing in S/3D TI heterostructures and magnetoelectric effects in the DOS.