Nonlinear susceptibility as a probe of tensor spin order inURu2Si2

Abstract
The nonlinear susceptibility is discussed as a probe of multispin correlation functions. In the heavy-fermion compound URu2 Si2, measurements of the leading nonlinear susceptibility (χ3) reveal a sharp anomaly at 17.3 K closely matching that of the specific heat at the same temperature. We attribute this result to the development of anisotropic triplet pairing in the particle-hole channel of the heavy electron fluid.