Abstract
The microscopic nature of the hidden order state in URu2Si2 is dependent on the low-energy configurations of the uranium ions, and there is currently no consensus on whether it is predominantly 5f(2) or 5f(3). Here we show that measurement of the basal-plane nonlinear susceptibility can resolve this issue; its sign at low temperatures is a distinguishing factor. We calculate the linear and nonlinear susceptibilities for specific 5f(2) and 5f(3) crystal-field schemes that are consistent with current experiment. Because of its dual magnetic and orbital character, a Gamma(5) magnetic non-Kramers doublet ground state of the U ion can be identified by chi(c)(1)(T) proportional to chi(perpendicular to)(3)(T), where we have determined the constant of proportionality for URu2Si2.