Incommensurate spin resonance in URu2 Si2

The nature of the hidden order (HO) in URu2 Si2 below THO =17.5 K has been a puzzle for a long time. Neutron-scattering studies of this material reveal a rich spin dynamics. We focus on the inelastic neutron scattering in URu2 Si2 and argue that the observed gap in the fermion spectrum naturally leads to the spin feature observed at energies ωres =4-6 meV at momenta at Q□ = (1±0.4,0,0). We discuss how spin features seen in URu2 Si2 can indeed be thought of in terms of the spin resonance that develops in HO state and is not related to the superconducting transition at 1.5 K. In our analysis, we assume that the HO gap is due to a particle-hole condensate that connects nested parts of the Fermi surface with nesting vector Q□ Within this approach, we can predict the behavior of the spin susceptibility at Q□ and find it to be strikingly similar to the phenomenology of resonance peaks in high Tc and heavy fermion superconductors. The energy of the resonance peak scales with THO ωres □4 kB THO. We discuss observable consequences that spin resonance will have on neutron scattering and local density of states. Moreover, we argue how the establishment of spin resonance in URu2 Si2 and better characterization of susceptibility, temperature, pressure, and Rh-doping dependence would elucidate the nature of the HO.