Triplet pairing states with equal spins in ferromagnet/superconductor heterojunctions for noncollinear magnetizations

Four-component Bogoliubov-de Gennes equations are applied to study tunneling conductance spectra of ferromagnet/ferromagnet/d-wave superconductor (F<Subscript>1</Subscript>/F<Subscript>2</Subscript>/d-wave S) tunnel junctions and to find out signs of spin-triplet pairing correlations induced in the proximity structure. The pairing correlations with equal spins arises from the novel Andreev reflection (AR), which requires at least three factors: the usual AR at the F<Subscript>2</Subscript>/S interface, spin flip in the F<Subscript>2</Subscript> layer, and superconducting coherence kept up in the F<Subscript>2</Subscript> layer. Effects of angle α between magnetizations of the two F layers, polarizations of the F<Subscript>1</Subscript> and F<Subscript>2</Subscript> layers, the thickness of the F<Subscript>2</Subscript> layer, and the orientation of the d-wave S crystal on the tunneling conductance are investigated. A conversion from a zero-bias conductance dip at α=0 to a zero-bias conductance peak at a certain value of α can be seen as a sign of generated spin-triplet correlations. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007