We report low-energy inelastic neutron scattering data of the paramagnetic (PM) to hidden-order (HO) phase transition at T0=17.5K in URu2Si2. While confirming previous results for the HO and PM phases, our data reveal a pronounced wave-vector dependence of low-energy excitations across the phase transition. To analyze the energy scans we employ a damped harmonic oscillator model containing a fit parameter 1/$\Gamma$ which is expected to diverge at a second-order phase transition. Counter to expectations the excitations at $̊ightarrow$Q1$\approx$(1.4,0,0) show an abrupt steplike suppression of 1/$\Gamma$ below T0, whereas excitations at $̊ightarrow$Q0=(1,0,0), associated with large-moment antiferromagnetism (LMAF) under pressure, show an enhancement and a pronounced peak of 1/$\Gamma$ at T0. Therefore, at the critical HO temperature T0, LMAF fluctuations become nearly critical as well. This is the behavior expected of a ``supervector'' order parameter with nearly degenerate components for the HO and LMAF leading to nearly isotropic fluctuations in the combined order-parameter space.     «

We report low-energy inelastic neutron scattering data of the paramagnetic (PM) to hidden-order (HO) phase transition at T0=17.5K in URu2Si2. While confirming previous results for the HO and PM phases, our data reveal a pronounced wave-vector dependence of low-energy excitations across the phase transition. To analyze the energy scans we employ a damped harmonic oscillator model containing a fit parameter 1/$\Gamma$ which is expected to diverge at a second-order phase transition. Counter to expe...     »