Field-dependent energy scales in URu2Si2

At low temperature, macroscopic properties of URu2Si2 display a characteris tic energy scale Delta(0)(B) which decreases when a magnetic field is appli ed, and eventually vanishes at an extrapolated value of the field of about 40 T. We have performed inelastic neutron scattering measurements of the ma gnetic dynamics of URu2Si2 in applied fields along the c axis of intensitie s up to 12 T. We show that Delta(0)(B) is not related to gaps in the magnet ic fluctuations spectra. This provides direct evidence of the fact that two distinct energy scales govern the physics of this compound.