Abstract
A bilayer quantum frustrated antiferromagnet is studied using an effective-action approach. For not very small values of interlayer coupling, the action derived from the microscopical Hamiltonian has the form of the quantum O(3) nonlinear sigma model. It is solved in the mean-field approximation with the ultraviolet cutoff chosen to fit numerical results. The obtained phase diagram displays a linear decrease in the critical value of interlayer coupling with increase of in-plane frustration.
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