Generating giant spin currents using nodal topological superconductors

Abstract

In this work, we show that a giant spin current can be injected into a nodal topological superconductor, using a normal paramagnetic lead, through a large number of zero-energy Majorana fermions at the superconductor edge. The giant spin current is caused by the selective equal-spin Andreev reflections (SESARs) induced by Majorana fermions. In each SESAR event, a pair of electrons with certain spin polarization are injected into the nodal topological superconductor, even though the pairing in the bulk of the nodal superconductor is spin-singlet $s$ wave. We further explain the origin of the spin current by showing that the pairing correlation at the edge of a nodal topological superconductor is predominantly equal-spin triplet at zero energy. The experimental consequences of SESARs in nodal topological superconductors are discussed.