Incommensurate spin resonance in URu2Si2.*

The nature of the hidden order (HO) in URu2Si2 below T$_{HO}$ = 17.5K has been a puzzle for a long time. Here we propose to search for the spin resonance as a tool to elucidate the nature of the HO. We consider inelastic neutron scattering in URu2Si2 and argue that a gap in the fermion spectrum will produce an incommensurate spin resonance at Q* = (1$\backslash $pm 0.4, 0,0) at $\omega _{res}$ = 4-6 meV. 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\^{}* . The predicted behavior of the spin susceptibility is strikingly similar to the phenomenology of resonance peaks in high-T{\_}c and heavy fermion superconductors. The energy of the resonance peak scales with T$_{HO}$ $\omega _{res} \quad \sim $ 4 k{\_}BT$_{HO}$