Basal-plane nonlinear susceptibility: A direct probe of the single-ion physics in URu2Si2

Abstract

he microscopic nature of the hidden order state in URu[subscript 2]Si[subscript 2] is dependent on the low-energy configurations of the uranium ions, and there is currently no consensus on whether it is predominantly 5f[supercript 2] or 5f[supercript 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[supercript 2] and 5f[supercript 3] crystal-field schemes that are consistent with current experiment. Because of its dual magnetic and orbital character, aΓ[subscript 5] magnetic non-Kramers doublet ground state of the U ion can be identified by χ[subscript 1][superscript c](T)∝χ[subscript 3]⊥(T), where we have determined the constant of proportionality for URu[subscript 2]Si[subscript 2].