title: Spin-current order in anisotropic triangular antiferromagnets.
abstract: We analyze instabilities of the collinear up-up-down state of a two-dimensional quantum spin-S spatially anisotropic triangular lattice antiferromagnet in a magnetic field. We find, within the large-S approximation, that near the end point of the plateau, the collinear state becomes unstable due to the condensation of two-magnon bound pairs rather than single magnons. The two-magnon instability leads to a novel two-dimensional vector chiral phase with alternating spin currents but no magnetic order in the direction transverse to the field. This phase breaks a discrete Z(2) symmetry but preserves a continuous U(1) one of rotations about the field axis. It possesses orbital antiferromagnetism and displays a magnetoelectric effect.
authors.affiliation: Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Andrey V
authors.initials: AV
authors.lastname: Chubukov
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Starykh