Basal-Plane Nonlinear Susceptibility: A Direct Probe of the Single-Ion Physics in URu2Si2

TL;DR

This paper demonstrates that basal-plane nonlinear susceptibility measurements can distinguish the uranium ion configurations in URu2Si2, clarifying the nature of its hidden order state by analyzing specific magnetic and orbital properties.

Contribution

It introduces a method to identify the uranium ion configuration in URu2Si2 using basal-plane nonlinear susceptibility, providing a new probe for the hidden order state.

Findings

Sign of nonlinear susceptibility at low temperatures differentiates 5f^2 and 5f^3 configurations.

Calculated susceptibilities match experimental data for specific crystal-field schemes.

Identified the a5 magnetic non-Kramers doublet ground state through susceptibility relations.

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 $\chi_1^c(T) \propto \chi_3^\perp(T)$ where we have determined the constant of proportionality for URu2Si2.