Nonlinear susceptibility:: Evidence for antiferroquadrupolar fluctuations and a nonmagnetic Γ1 ground state in the heavy fermion superconductor PrOs4Sb12

Nonlinear susceptibility (chi(3)) measurements were performed on single crystals of the heavy fermion superconductor PrOs4Sb12 in order to probe the nature of the Pr3+ ground state in the crystalline electric field. Calculations of chi(3)(T) have been carried out (i) within a mean field model of intersite magnetic and quadrupolar interactions for an ionic (zero hybridization) crystal field Gamma(1) singlet ground state and a first excited state magnetic triplet, and (ii) within a two-channel Anderson impurity model assuming a Gamma(23) doublet ground state. The experimental chi(3) results are in best agreement with the nonmagnetic Gamma(1) ground state in the tetrahedral crystalline electric field of the Pr3+ ions with antiferroquadrupolar intersite coupling and weak antiferromagnetic intersite coupling.