The quantum ferromagnetic transition of itinerant electrons is considered. It is shown that the Landau-Ginzburg-Wilson theory described by Hertz and others breaks down due to a singular coupling between fluctuations of the conserved order parameter. This coupling induces an effective long-range interaction between the spins of the form 1/r2d-1. It leads to unusual scaling behavior at the quantum critical point in 1 < d ≤ 3 dimensions, which is determined exactly.
T. Vojta et al., "Breakdown of Landau-Ginzburg-Wilson Theory for Certain Quantum Phase Transitions," Europhysics Letters, vol. 36, no. 3, pp. 191-196, Institute of Physics - IOP Publishing, Oct 1996.
The definitive version is available at http://dx.doi.org/10.1209/epl/i1996-00208-x
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