Browsing by Author "Arjoranta, Juho"

The spin-orbit (SO) coupling gives rise to a large splitting of the subband energy levels in semiconducting heterostructures. Both theoretical and experimental interest towards SO interactions in superconductors and superconducting heterostructures has been on the rise due to new experimental findings on the field. The zero-energy peak in the local density of states in the experiment suggests that Majorana fermions appear in superconductor-semiconductor nanowires. In this thesis, I study the effects of SO coupling in superconductor-normal metal-superconductor (SNS) junctions in the presence of an exchange field. We adopt the quasiclassical Green's function approach and implement the Rashba SO interaction into the Usadel equation, which is the equation of motion for the quasiclassical Green's functions. We solve the Usadel equation numerically as the analytic solution in the general case is not possible. We find that the Rashba SO coupling has a finite effect on the physical properties of the junction only if there is also an exchange field along the SNS junction. When both are present, two interesting phenomena occur. Contrary to the case without Rashba SO coupling, supercurrent through the SNS junction stays finite even with a very large exchange field strength along the junction. Also, the local density of states peaks up in the normal metal at zero energy when both, the exchange field and the Rashba SO coupling, are present. The peak persists almost throughout the normal metal regime vanishing only at the edges near the superconductors. Therefore, the peak cannot be explained as Majorana fermions as they would appear as a peak near the edges and an alternative explanation is needed.