Quadrupolar Phase Transition and Field-Dependent Multipolar Fluctuation in CeB₆

Abstract

The effect of multipolar fluctuations on the quadrupolar phase transition in CeB₆ is investigated. The d^-1-correction to the mean-field solution of the multipolar Ruderman-Kittel-Kasuya-Yoshida (RKKY) model is analyzed in terms of a generalized Landau expansion of free energy, with d being the spatial dimension. It is shown that the multipolar fluctuations become strong and field-dependent when the model is close to the SU(4)-symmetric limit. As a result, various unusual phenomena around the transition are shown to be reasonably explained within the RKKY model. The realistic form of the interactions for CeB₆ is discussed on the basis of a quantitative comparison with experiments.