Dynamical properties of spatially anisotropic frustrated Heisenberg models in a magnetic field

We investigate spectral features of spatially anisotropic spin-1/2 frustrated antiferromagnets in a magnetic field by a weak-coupling approach from the one-dimensional (1D) limit. Using exact results of the Heisenberg chain, we calculate dynamical structure factors of spatially anisotropic frustrated antiferromagnets in two dimensions. We obtain rich peak structures depending on the momentum and the strength of magnetic fields. We identify the sharp peaks as bound and antibound states between particles carrying fractional S^z in 1D in a magnetic field, psinons and antipsinons, and those originating from 2-string solutions. We compare these spectral features with available experimental results on Cs₂CuCl₄, and suggest that the dynamical properties of Cs₂CuCl₄ in a magnetic field can be interpreted in terms of particles in 1D in a magnetic field.