Spin current and magnetoelectric effect in noncollinear magnets

A new mechanism of the magnetoelectric effect based on the spin supercurrent is theoretically presented in terms of a microscopic electronic model for noncollinear magnets. The electric polarization (P) over right arrow (ij) produced between the two magnetic moments (S) over right arrow (i) and (S) over right arrow (j) is given by (P) over right arrow proportional to e(ij)x((S) over right arrow (i)x (S) over right arrow (j)) with (e) over right arrow (ij) being the unit vector connecting the sites i and j. Applications to the spiral spin structure and the gauge theoretical interpretation are discussed.