Evidence for a hidden order parameter in URu₂Si₂

Proceedings of the International Conference on Magnetism (ICM 2003)We have measured the field dependence of the ordered antiferromagnetic moment and the magnetic excitations in URu2Si2 for fields up to 17 T applied along c axis, using neutron scattering. The decrease of the magnetic intensity of the tiny moment m with increasing field does not follow a simple power law, but shows a clear inflection point, suggesting that the moment m is connected to a hidden order parameter Ψ. The magnetic excitation gap at Q=(1,0,0) increases continuously with increasing field, while that at Q=(1.4,0,0) is nearly constant