One-step replica symmetry breaking solution for fermionic Ising spin glass in a transverse field

The fermionic Ising spin glass models in a transverse field are investigated in a Grassmann path integral formalism. The Parisi's scheme of one-step replica symmetry breaking (RSB) is used within the static ansatz. This formalism has already been applied in a theory in which $m$ (Parisi's block-size parameter) is taken as a constant (PRB 72, 014447 (2005)). Now, it is extended to consider $m$ as a variational parameter. In this case, the results show that RSB is present when $T\to0$, in which the system is driven by quantum fluctuations.Comment: 8 pages, 3 figures, accepted for publication as a Brief Report in Phys. Rev.

A van Hemmen-Kondo model for disordered strongly correlated electron systems

We present here a theoretical model in order to describe the competition between the Kondo effect and the spin glass behavior. The spin glass part of the starting Hamiltonian contains Ising spins with an intersite exchange interaction given by the local van Hemmen model, while the Kondo effect is described as usual by the intrasite exchange $J_K$. We obtain, for large $J_K$ values, a Kondo phase and, for smaller $J_K$ values, a succession, with decreasingComment: 14 pages, 4 figures, accepted for publication in Phys. Rev.

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Role of the transverse field in inverse freezing in the fermionic Ising spin-glass model

We investigate the inverse freezing in the fermionic Ising spin-glass (FISG) model in a transverse field $\Gamma$. The grand canonical potential is calculated in the static approximation, replica symmetry and one-step replica symmetry breaking Parisi scheme. It is argued that the average occupation per site $n$ is strongly affected by $\Gamma$. As consequence, the boundary phase is modified and, therefore, the reentrance associated with the inverse freezing is modified too.Comment: 6 pages, 3 figures, accepted for publication in PR

Spin Glass and antiferromagnetism in Kondo lattice disordered systems

The competition between spin glass (SG), antiferromagnetism (AF) and Kondo effect is studied here in a model which consists of two Kondo sublattices with a gaussian random interaction between spins in differents sublattices with an antiferromagnetic mean Jo and standard deviation J. In the present approach there is no hopping of the conduction electrons between the sublattices and only spins in different sublattices can interact. The problem is formulated in the path integral formalism where the spin operators are expressed as bilinear combinations of Grassmann fields which can be solved at mean field level within the static approximation and the replica symmetry ansatz. The obtained phase diagram shows the sequence of phases SG, AF and Kondo state for increasing Kondo coupling. This sequence agrees qualitatively with experimental data of the Ce_{2} Au_{1-x} Co_{x} Si_{3} compound.Comment: 7 pages, 1 figure, submitted to EPJ