INCOMMENSURATE SPIN CORRELATIONS IN SPIN-1 2 FRUSTRATED 2-LEG HEISENBERG LADDERS/

We develop a low-energy effective theory for spin-1/2 frustrated two-l eg Heisenberg spin ladders. We obtain a new type of interchain couplin g that breaks parity symmetry. In the presence of an XXZ-type anisotro py, this interaction gives rise to a novel ground state, characterized by incommensurate correlations. In the case of a single ladder, this state corresponds to a spin nematic phase. For a frustrated quasi-one- dimensional system of infinitely many weakly coupled chains, this stat e develops true three-dimensional spiral order. We apply our theory to recent neutron scattering experiments on Cs2CuCl4.