Gapped Excitations in the High-Pressure Antiferromagnetic Phase of   URu$_2$Si$_2$
  We report a neutron scattering study of the magnetic excitation spectrum in each of the three temperature and pressure driven phases of URu$_2$Si$_2$. We find qualitatively similar excitations throughout the (H0L) scattering plane in the hidden order and large moment phases, with no changes in the $\hbar\omega$-widths of the excitations at the $\Sigma$ = (1.407,0,0) and $Z$ = (1,0,0) points, within our experimental resolution. There is, however, an increase in the gap at the $\Sigma$ point from 4.2(2) meV to 5.5(3) meV, consistent with other indicators of enhanced antiferromagnetism under pressure. 
T.J. Williams, H. Barath, Z. Yamani, J.A. Rodriguez-Riviera, J.B.   Le\~ao, J.D. Garrett, G.M. Luke, W.J.L. Buyers and C. Br...
cond-mat.str-el