Symmetry and correlations underlying Hidden Order in URu2Si2

We experimentally investigate the symmetry in the Hidden Order (HO) phase of intermetallic URu2Si2 by mapping the lattice and magnetic excitations via inelastic neutron and x-ray scattering measurements in the HO and high-temperature paramagnetic phases. At all temperatures the excitations respect the zone edges of the body-centered tetragonal paramagnetic phase, showing no signs of reduced spatial symmetry, even in the HO phase. The magnetic excitations originate from transitions between hybridized bands and track the Fermi surface, whose feature are corroborated by the phonon measurements. Due to a large hybridization energy scale, a full uranium moment persists in the HO phase, consistent with a lack of observed crystal-field-split states. Our results are inconsistent with local order parameter models and the behavior of typical density waves. We suggest that an order parameter that does not break spatial symmetry would naturally explain these characteristics.
Comment: 16 pages, 13 figures The scope of this work was expanded to include much more magnetic neutron scattering as well as inelastic x-ray scattering. The modes originally identified as soft phonons are magnetic. Many of the figures had their quality reduced in order to fit the arxiv file size limits. Please see the PRB article for higher quality images