Magnetic excitations in URu$_2$Si$_2$ paramagnetic and Hidden Order phases

We have mapped the lattice and magnetic excitations in heavy fermion URu$_2$Si$_2$ via inelastic neutron and x-ray scattering measurements in the Hidden Order and paramagnetic phases. The magnetic excitations and phonons always respect the zone edges of the paramagnetic phase, showing no signs of reduced spatial symmetry. Features of the magnetic and lattice excitation spectra are associated with effects due to electronic interactions. Our results are inconsistent with simple local order parameters and density waves, and place constraints on models invoking Brillouin zone folding of the magnetic excitations. Phys. Rev. B 91, 035128 (2015)