[show abstract][hide abstract] ABSTRACT: The crossover between an impurity band (IB) and a valence band (VB) regime as a function of the magnetic impurity concentration in a model for diluted magnetic semiconductors (DMSs) is studied systematically by taking into consideration the Coulomb attraction between the carriers and the magnetic impurities. The density of states and the ferromagnetic transition temperature of a spin-fermion model applied to DMSs are evaluated using dynamical mean-field theory and Monte Carlo (MC) calculations. It is shown that the addition of a square-well-like attractive potential can generate an IB at small enough Mn doping x for values of the p-d exchange J that are not strong enough to generate one by themselves. We observe that the IB merges with the VB when x⩾xc where xc is a function of J and the Coulomb strength V. Using MC simulations, we demonstrate that the range of the Coulomb attraction plays an important role. While the on-site attraction, which has been used in previous numerical simulations, effectively renormalizes J for all values of x, an unphysical result, a nearest-neighbor range attraction renormalizes J only at very low dopings, i.e., until the bound holes wave functions start to overlap. Thus, our results indicate that the Coulomb attraction can be neglected to study Mn-doped GaSb, GaAs, and GaP in the relevant doping regimes, but it should be included in the case of Mn-doped GaN, which is expected to be in the IB regime.
[show abstract][hide abstract] ABSTRACT: Recent progress in the numerical study of various strongly correlated electronic systems is reviewed. The study of transport in single molecule conductors and quantum dots is addressed with a recently proposed adaptive time-dependent density-matrix-renormalization group (DMRG). Experiments involving non-local spin control and their numerical simulation are also discussed. A section is devoted to recent efforts in the study of spin-fermion models for colossal magnetoresistive manganites, where we present insights on the effect of disorder and electron–phonon coupling. Finally, using a dynamical mean field approach, we review calculations in the area of diluted magnetic semiconductors that provides guidelines on how the Curie temperature could be increased in these itinerant ferromagnetic systems.