Roles of Quadrupoles in Non-Fermi Liquid Physics for Crystal Field Triplets

Abstract

Crystal field triplet ground states in f(2) configurations such as Pr ions have quadrupolar coupling as well as magnetic coupling to conduction electrons, leading to a nontrivial non-Fermi liquid Kondo physics associated with quadrupole degrees of freedom. In particular, a magnetic-field-induced quadrupole moment exhibits the same power-law temperature dependence as a magnetic moment, which is demonstrated by a numerical renormalization group analysis. Both thermodynamic quantities are also scaled by a single energy parameter as well as a quadrupole susceptibility, indicating that magnetic dipoles and electric quadrupoles are closely correlated. The field-induced quadrupoles may be relevant for confirmation of the Kondo effect of triplet origin, which could cause unusual heavy fermion properties of Pr-based metallic compounds.