Spin-triplet pairs in the proximity of a supercondutor and a ferromagnet

Electrons in a supercondutor below Tc are described by a single wave function, which satifies Schrodinger's equation (dBG equation). The value of this function relates to the effective potential felt by the Copper pairs. The potential is negative in the superconductor but positive in a normal material. Thus, normal mateials make a energy barrier that prevents the peameability of electron pairs , and hence supercurrent to spill much, especially when the normal material is ferromagnetic. A ferromagnet favors spin-triplet, while Copper pairs are singlets. Nevertheless, there are some recent experiments observing a longer-range spilling of supercurrent, which was being put under the context of spin-triplet paring that may arise the perephery of an S-N interaface. Now, it came a paper aiming at this problem[1]. They found further evidences of such paring.

The superconductor-ferromagnet proximity effect describes the fast decay of a spin-singlet supercurrent originating from the superconductor upon entering the neighboring ferromagnet. After placing a conical magnet (holmium) at the interface between the two, we detected a long-ranged supercurrent in the ferromagnetic layer. The long-range effect required particular thicknesses of the spiral magnetically ordered holmium, consistent with spin-triplet proximity theory. This enabled control of the electron pairing symmetry by tuning the degree of magnetic inhomogeneity through the thicknesses of the holmium injectors.

[1]Science 2 July 2010: Vol. 329. no. 5987, pp. 59 - 61; DOI: 10.1126/science.1189246