Influence of Spin-Orbit Interactions on Point Contact Andreev Reflection

In PCAR (point contact Andreev reflection) the I(V) characteristics of an interface between a singlet superconductor and a ferromagnetic metal is used (1)(2) to probe the degree of spin-polarization near the Fermi energy of the ferromagnet. Motivated by recent PCAR studies (3)(4) of (III,Mn)V ferromagnetic semiconductors, in which the spin-orbit interaction scale is comparable to the exchange energy scale, we report on a theoretical study the effect of spin-orbit interactions on the quasiparticle current through a ferromagnet-superconductor interface. Our theoretical analysis generalizes the Blonder-Tinkham-Klapwijk model results commonly used to interpret PCAR experiments. We find that PCAR provides a good qualitative measure of Fermi energy spin-polarization, even when the quasiparticle bands are strongly spin-orbit coupled.\\ (1) R.J. Soulen \emph{et al.}, Science \textbf{282},85 (1998)\\ (2) S.K. Upadhyay \emph{et al.}, Phys. Rev Lett. \textbf{81}, 3247 (1998)\\ (3) J.G. Braden \emph{et al.}, Phys. Rev. Lett. \textbf{91},56602 (2003)\\ (4) R.P. Pangulury \emph{et al.}, Appl. Phys. Lett. \textbf{84},4947 (2004)