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

摘要

Four-component Bogoliubov-de Gennes equations are applied to study tunneling conductance spectra of ferromagnet/ferromagnet/d-wave superconductor (F-1/F-2/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-2/S interface, spin flip in the F-2 layer, and superconducting coherence kept up in the F-2 layer. Effects of angle alpha between magnetizations of the two F layers, polarizations of the F-1 and F-2 layers, the thickness of the F-2 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 alpha = 0 to a zero-bias conductance peak at a certain value of alpha can be seen as a sign of generated spin-triplet correlations.