Effective model of the electronic Griffiths phase

We present simple analytical arguments explaining the universal emergence of electronic Griffiths phases as precursors of disorder-driven metal-insulator transitions in correlated electronic systems. A simple effective model is constructed and solved within Dynamical Mean Field Theory. It is shown to capture all the qualitative and even quantitative aspects of such Griffiths phases.Comment: 9 pages, 7 figures, one reference corrected; minor corrections include

Non-uniform phases in metals with local moments

The two-dimensional Kondo lattice model with both nearest and next-nearest neighbor exchange interactions is studied within a mean-field approach and its phase diagram is determined. In particular, we allow for lattice translation symmetry breaking. We observe that the usual uniform inter-site order parameter is never realized, being unstable towards other more complex types of order. When the nearest neighbor exchange J_1 is ferromagnetic the flux phase is always the most stable state, irrespective of the value of the next-nearest-neighbor interaction J_2. For antiferromagnetic J_1, however, either a columnar or a flux phase is realized, depending on conduction electron filling and the value of J_2.Comment: 5 pages, 7 figure