Niklowitz, P. G. (Corresponding Author) ; Dunsiger, S. R. ; Pfleiderer, C.MLZ* ; Link, P.MLZ* ; Schneidewind, A.MLZ* ; Faulhaber, E.MLZ* ; Vojta, M. ; Huang, Y. -. ; Mydosh, J. A.

2015

Abstract: We report low-energy inelastic neutron scattering data of the paramagnetic (PM) to hidden-order (HO) phase transition at $T_0=17.5\,{\rm K}$ in URu$_2$Si$_2$. While confirming previous results for the HO and PM phases, our data reveal a pronounced wavevector 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 $\vec{Q}_1=(1.44,0,0)$ show an abrupt step-like suppression of $1/\Gamma$ below $T_0$, whereas excitations at $\vec{Q}_0=(1,0,0)$, associated with large-moment antiferromagnetism (LMAF) under pressure, show an enhancement and a pronounced peak of $1/\Gamma$ at $T_0$. Therefore, at the critical HO temperature $T_0$, LMAF fluctuations become nearly critical as well. This is the behavior expected of a super-vector order parameter with nearly degenerate components for the HO and LMAF leading to nearly isotropic fluctuations in the combined order-parameter space.

Keyword(s): Key Technologies (1st) ; Fundamental Science (1st) ; Magnetism (2nd)

1. PANDA
2. ICTRL
3. OPTIC
4. E21

1. PANDA: Cold three axes spectrometer (SR2)