Quantum critical properties of the Bose-Fermi Kondo Model in a large-N limit

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Studies of non-Fermi liquid properties in heavy fermions have led to the current interest in the Bose-Fermi Kondo model. Here we use a dynamical large-N approach to analyze an SU(N)xSU(κN) generalization of the model. We establish the existence in this limit of an unstable fixed point when the bosonic bath has a sub-ohmic spectrum (|ω|¹⁻ε ω, with 0<ε<1). At the quantum critical point, the Kondo scale vanishes and the local spin susceptibility (which is finite on the Kondo side for κ<1) diverges. We also find an ω/T scaling for an extended range (15 decades) of ω/T. This scaling violates (for ε≥ 1/2) the expectation of a naive mapping to certain classical models in an extra dimension; it reflects the inherent quantum nature of the critical point.