Abstract
A system exhibiting multiple simultaneously broken symmetries offers the opportunity to influence physical phenomena such as tunneling currents by means of external control parameters. In this paper, we consider the broken SU(2) (internal spin) symmetry of ferromagnetic systems coexisting with (i) the broken U(1) symmetry of superconductors and (ii) the broken spatial inversion symmetry induced by a Rashba term in a spin-orbit coupling Hamiltonian. In order to study the effect of these broken symmetries, we consider tunneling currents that arise in two different systems; tunneling junctions consisting of nonunitary spin-triplet ferromagnetic superconductors and junctions consisting of ferromagnets with spin-orbit coupling. In the former case, we consider different pairing symmetries in a model where ferromagnetism and superconductivity coexist uniformly. An interplay between the relative magnetization orientation on each side of the junction and the superconducting phase difference is found, similarly to that found in earlier studies on spin-singlet superconductivity coexisting with spiral magnetism. This interplay gives rise to persistent spin- and charge-currents in the absence of an electrostatic voltage that can be controlled by adjusting the relative magnetization orientation on each side of the junction. In the second system, we study transport of spin in a system consisting of two ferromagnets with spin-orbit coupling separated by an insulating tunneling junction. A persistent spin-current across the junction is found, which can be controlled in a well-defined manner by external magnetic and electric fields. The behavior of this spin-current for important geometries and limits is studied.
- Received 6 September 2006
DOI:https://doi.org/10.1103/PhysRevB.75.024508
©2007 American Physical Society