Non-Fermi Liquid Fixed Points in Quantum Impurity Models:Non-perturbative Approaches
(séminaire commun avec : LPS, CPhT et LPTMS d’Orsay)
Four decades ago, the work of the Japanese physicist Jun Kondo was the beginning of intense theoretical studies of the effects of impurities in metals. A problem that found later many ramifications, -in applications to heavy fermions, mesoscopics, etc.-, and constitutes one of the current paradigms of strongly-correlated many-body physics. I will present the Kondo and Anderson models and their multi-channel generalizations; giving a discussion of the different non-perturbative approaches used to study their non-trivial infrared fixed points.
I will put the emphasis on the case of multi-channel impurities. In particular, I will give a summarized account of our most recent results for the multi-channel Anderson model. We studied the full crossovers of different thermodynamic quantities, and we have shown that the low-energy physics of this model is governed by a line of fixed points. This describes non-Fermi liquid behavior in the integral valence regime, associated with moment formation, as well as in the mixed valence regime, where no moment forms. I will briefly point out the relevance of these results for the theory of certain uranium heavy fermion compounds like UBe$_{13}$.
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