Recent developments in multi-channel Kondo physics (invited) (abstract)

Abstract

The two-channel Kondo model for a single spin-one-half magnetic impurity coupled to two degenerate bands of conduction electrons predicts the existence of a zero-temperature quantum critical point, leading to ‘‘marginal-Fermi-liquid’’ behavior at low temperatures. A two-channel Kondo description has been proposed1 for several U and Ce-based heavy-fermion materials whose thermodynamic and transport properties exhibit anomalous temperature and magnetic field dependence.2 This talk will review recent theoretical work on multi-channel Kondo behavior. Two factors may be particularly important in determining the relevance of the multi-channel Kondo effect for real systems: (1) Channel asymmetry: Any difference between the coupling of the two conduction bands to the impurities leads to the recovery of Fermi-liquid behavior at sufficiently low temperatures.3 (2) Inter-impurity interactions: Numerical renormalization-group calculations for a two-impurity model show that any nonzero Ruderman–Kittel–Kasuya–Yoshida (RKKY) coupling between the impurities destabilizes the single-impurity critical point.4 Depending on the strength and sign of the RKKY coupling, the system may be driven either to a Fermi-liquid or to a novel regime of non-Fermi-liquid behavior governed by nonuniversal critical exponents. The experimental implications of these findings will be discussed.