IC state, by contrast to the cone state, spins on alternate chains in the plane precess in the opposite sense. []{data-label="fig:ic-state"}](ic_gray.pdf){width="0.95\columnwidth"}

One noteworthy highlight is that, remarkably, when the magnetic field is in the $b$-$c$ plane, the spin correlations impugn the popular interpretation of [[Cs$_2$CuCl$_4$]{}]{} as a two-dimensional “anisotropic triangular lattice” antiferromagnet. In fact, in this very wide regime, in the ground state, the spins are more correlated in the $a$-$b$ planes, [*perpendicular*]{} to the triangular layers, than they are within those layers! Taking into account these correlations is crucial to obtaining the proper low temperature phase diagram. They lead to an enhanced sensitivity to some very weak second neighbor and effective “biquadratic” interactions, which are needed to stabilize the antiferromagnetic and incommensurate states mentioned above.

The remainder of the paper is organized as follows. In Sec. \[sec:background\], we present some necessary background, including the standard model Hamiltonian for [[Cs$_2$CuCl$_4$]{}]{}, the low energy properties of a single Heisenberg chain, the results of a space group analysis of allowed DM interactions in [[Cs$_2$CuCl$_4$]{}]{}, and a summary of the general scaling and Chain Mean Field Theory (CMFT) approach to studying competing interactions. In Sec. \[sec:ideal-2d-model\], we determine the ground state behavior of 