Heavy-fermion and spin-liquid behavior in a Kondo lattice with magnetic frustration

We study the competition between the Kondo effect and frustrating exchange interactions in a Kondo-lattice model within a large-N dynamical mean-field theory. We find a T=0 phase transition between a heavy Fermi liquid and a spin liquid for a critical value of the exchange J(c)=T-K(0), the single-impurity Kondo temperature. Close to the critical point, the Fermi-liquid coherence scale T-star is strongly reduced and the effective mass strongly enhanced. The regime T>T-star is characterized by spin-liquid magnetic correlations and non-Fermi-liquid properties. It is suggested that magnetic frustration is a general mechanism which is essential to explain the large effective mass of some metallic compounds such as LiV2O4.