Frustration in the Kondo lattice model: Local versus extended singlet phases
Résumé
We present a theoretical study of the frustrated Kondo lattice model on a Shastry-Sutherland-type lattice. Using a mean-field decoupling on both the Kondo and intersite exchange interactions, we study three different phases, an antiferromagnetic (AF) phase without Kondo effect, a Kondo (K) phase without magnetic order, and finally a valence bond solid (VBS) phase without magnetic order and Kondo effect. A phase diagram is obtained giving the stability region of the three phases, as a function of the Kondo parameter JK and the frustration ratio J/J' of the two exchange interactions on the Shastry-Sutherland lattice. This phase diagram can account for the change under pressure from a nonmagnetic Kondo phase to an AF phase and to a completely different nonmagnetic VBS phase occurring in some ytterbium compounds such as Yb2Pd2Sn.