Quantum fluctuations in the incommensurate phase of CsCuCl3 under transverse magnetic field

In low magnetic field, the stacked, triangular antiferromagnet CsCuCl3 has a helical structure incommensurate (IC) in the chain direction. The IC wavenumber (from neutron–diffraction experiments) decreases with increasing field transverse to the chains, as predicted by classical theory, but then it has a plateau almost certainly caused by quantum fluctuations. Linear spin– wave theory fails because fluctuations have particularly large effects in the IC phase. An innovative phenomenological treatment of quantum fluctuations yields a plateau at approximately the observed value and the observed fields; it predicts a transition to the commensurate phase so far not observed. Results depend sensitively on a weak anisotropy. 64.70.Rh, 75.10.Jm, 75.25.+z, 75.50.Ee Typeset using REVTEX