Replica symmetry breaking in a quantum spin glass-antiferromagnetic Kondo lattice

The competition between the Kondo effect and the glassy magnetic order has been studied in a theoretical model of a Kondo lattice with an intrasite Kondo interaction. The spin glass (SG) and the antiferromagnetic (AF) orderings are described by two Kondo sublattices with infinite-range Ising SG interactions among localized spins and the disordered interactions can occur with spins of same sublattices and between spins of distinct sublattices. A transverse field F is introduced in the effective model as a quantum mechanism to produce spin flipping. The problem is formulated in a Grassmann path integral formalism. The disorder is treated within the replica trick in one-step replica symmetry breaking (1S-RSB). The static ansatz is adopted to get a mean-field expression for the free energy and order parameters. Results show a transition from the AF order to an RSB region with a finite staggered magnetization (mixed phase) when temperature T decreases for low values of the Kondo interaction. The SG phase is not observed below the mixed phase for 1S-RSB solution, in contrast with previous replica symmetry (RS) results. The F field suppresses the Neel temperature leading it to a quantum critical point. (C) 2007 Elsevier B.V. All rights reserved.