Role of commensurate and incommensurate low-energy excitations in the paramagnetic to hidden-order transition of URu2Si2. / Niklowitz, P. G.; Dunsiger, Sarah; Pfleiderer, C.; Link, P.; Schneidewind, Astrid; Faulhaber, Enrico; Vojta, M.; Huang, Y. -K.; Mydosh, J. A.

In: Physical Review B, Vol. 92, No. 11, 115116, 08.09.2015, p. 1-6.

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• P. G. Niklowitz
• Sarah Dunsiger
• C. Pfleiderer
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 quasielastic scattering {\em across} the phase transition. Temperature scans at a small energy transfer of $0.5$~meV establish an abrupt step-like suppression of the excitations at $\vec{Q}_1=\qone$ below $T_0$, whereas excitations at $\vec{Q}_0=\qzero$, associated with large-moment antiferromagnetism (LMAF) under pressure, are enhanced with a pronounced peak {\em at} $T_0$. 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.