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 Jc = T 0 K , the single-impurity Kondo temperature. Close to the critical point, the Fermi liquid coherence scale T ⋆ is strongly reduced and the effective mass strongly enhanced. The regime T > T ⋆ is characterized by spin-liquid magnetic correlations and non-Fermi-liquid properties. It is suggested that some of these considerations are relevant to the heavy fermion compound LiV2O4 and that magnetic frustration is essential to explain the large effective mass and small coherence scale observed in this compound. Introduction. – The interplay between the Kondo effect and RKKY interactions is an essential feature of heavy-fermion systems. In dilute Kondo systems, below the single-site Kondo temperature T 0 K , local magnetic moments are screened and a local Fermi-liquid (FL) picture applies [1]. In dense systems, intersite interactions between the localized spins compete with the Kondo effect and may lead to a magnetically ordered ground state if they are strong enough [2]. In the presence of frustration (either due to the geometry of the lattice or to disorder), conventional magnetic ordering may be replaced by spin-glass (SG) freezing, or be suppressed altogether, leaving a correlated paramagnet or “spin-liquid” (SL) state. This situation is apparently realized in LiV2O4, a metallic compound which displays heavyfermion behavior even though no f-electrons are involved [3–5]. Similar physics may be present in YScMn2 and β −Mn. LiV2O4 has a normal-spinel structure in which the V ions form a lattice of corner-sharing tetrahedra. This highly frustrated structure is known to lead to unconventional spin-liquid ground-states [6] and recent NMR studies [7] indeed showed (∗) E-mail:[email protected]