Manifestation of triplet superconductivity in superconductor-ferromagnet structures

We study proximity effects in a multilayered superconductor/ferromagnet (S/F) structure with arbitrary relative directions of the magnetization M. If the magnetizations of different layers are collinear, the superconducting condensate function induced in the F layers has only a singlet component and a triplet one with a zero projection of the total magnetic moment of the Cooper pairs on the M direction. In this case the condensate penetrates the F layers over a short length ξ_J determined by the exchange energy J. If the magnetizations M are not collinear, the triplet component has, in addition to the zero projection, the projections ±1. The latter component is even in the momentum, odd in the Matsubara frequency and penetrates the F layers over a long distance that increases with decreasing temperature and does not depend on J (the spin-orbit interaction limits this length). If the thickness of the F layers is much larger than ξ_J, the Josephson coupling between neighboring S layers is provided only by the triplet component, so that a new type of superconductivity arises in the transverse direction of the structure. The Josephson critical current is positive (negative) for the case of a positive (negative) chirality of the vector M. We demonstrate that this type of the triplet condensate can be detected also by measuring the density of states in F/S/F structures.