RKKY interaction in layered superconductors with anisotropic pairing

The RKKY interaction between localized moments in layered d-wave superconductors is considered at T much less than T-c. It is shown that the interaction is anisotropic and consists of two terms: conventional oscillating one and the positive term, which is proportional to the gap function and decreases in the 2D case inversely proportional to the distance. Both of these terms reveal crossover to the more rapid decay law at large distances, exponential one away from the nodal directions of order parameter and power-like law close to them. If the background in the normal state is ferromagnetic, d-wave superconductivity results in helicoid ordering with a star of helicoid axes fixed by nodes. The period of this skew structure has unconventional xi(1/2) dependence on the correlation length.