Spin current in triplet superconducting rings

Full text: In the BCS theory, superconductivity is characterized by the condensation of Cooper pairs which consist of two electrons. The spin configurations of Copper pairs are categorized into spin-singlet state and spin-triplet states. This feature can be described by the pair potentials in a matrix form. On the basis of the mean field theory of superconductivity [2], we derive a formula of spin current in spin-triplet superconducting systems. We found that the spatial fluctuations of d-vectors drive the spin current in equilibrium. Here we consider spin current in topological crystals [3] of spin-triplet superconductors as shown in Fig.1 (a). The solid vectors denote the d-vector of the pair potentials. There is no spin current in a ring shown in (a) because there is no spatial fluctuations in d-vectors. In (b) and (c), however, d-vector is rotated by 2π while it circles the ring, which causes the circulating spin current polarized perpendicular to the d-vectors. In the presentation, we will also discuss a relation between the polarization of spin and the current direction. [1] Y. Maeno, et. al., Nature 372, 532 (1994). [2] Y. Asano, Phys. Rev. B 64, 224515 (2001). [3] S. Tanda et al., Nature 417, 397 (2002). (There is one figure also)