Effect of helical edge states on the tunneling conductance in ferromagnet/noncentrosymmetric superconductors junctions

Abstract

Helical edge states exist in the mixed spin-singlet and spin-triplet phase of a noncentrosymmetric (NCS) superconductor. In this article we have considered a planar ferromagnetic metal/NCS superconductor tunnel junction and have studied the effect of these helical edge states which manifests itself through the charge and spin tunneling conductance across the junction. We have shown the behavior of conductances for the entire range of variation of $\gamma = \Delta_-/\Delta_+$ where $\Delta_\pm$ are the order parameters in the positive and negative helicity bands of the NCS superconductor.There exists a competition between the Rashba parameter $\alpha$ and the exchange energy $E_{ex}$ which is crucial for determining the variation of the conductance with the applied bias voltage across the junction. We have found a nonzero spin current across the junction which appears due to the exchange energy in the Ferromagnet and modulates with the bias voltage. It also changes its profile when the strength of the exchange energy is varied.