Spin polarization of (Ga,Mn)As measured by Andreev Spectroscopy: The role of spin-active scattering

Abstract

We investigate the spin-polarization of the ferromagnetic semiconductor(Ga,Mn)As by Andreev point contact spectroscopy. We analyze the conductancespectra with the theoretical model of [R. Grein et al., Phys. Rev. B 81, 094508(2010)], which accounts for momentum- and spin-dependent scattering at theinterface. We show that this allows for fitting the data without resorting toan effective temperature or statistical distribution of superconducting gaps,as it is the case for the spin-dependent version of the standardBlonder-Tinkham-Klapwijk (BTK) model. We find a transport polarization PC ofabout 56% at the Fermi level and comparing it to the k.p kinetic-exchange modelof (Ga,Mn)As, we achieve a considerably better agreement than estimatesinferred from the spin-dependent BTK model which are significantly higher. Thetemperature dependence of the conductance spectra is fully analyzed.