Giant spin splitting and $0 - π$ Josephson transitions from the Edelstein effect in quantum spin-Hall insulators

G. Tkachov

Published 2017-03-17Version 1

Hybrid structures of quantum spin-Hall insulators (QSHIs) and superconductors present a unique opportunity to access dissipationless topological states of matter, which, however, is frequently hindered by the lack of control over the spin polarization in QSHIs. We propose a very efficient spin-polarization mechanism based on the magnetoelectric (Edelstein) effect in superconducting QSHI structures. It acts akin to the Zeeman splitting in an external magnetic field, but with an effective g-factor of order of 1000. We show that the Edelstein spin splitting triggers $0-\pi$ Josephson transitions with a superharmonic $\pi$-periodic current-phase relationship at the transition. This manifests itself as a crossover from $\Phi_0$ - to $\Phi_0/2$ - periodic magnetic oscillations of the Josephson current in a superconducting loop ($\Phi_0=h/2e$ is the magnetic flux quantum). Such controllable $0-\pi$ transitions offer new perspectives for dissipationless spintronic devices and engineering flux qubits.