Large-Scale Monte Carlo Study of a Realistic Lattice Model forGa1−xMnxAs

Abstract

The properties of Mn-doped GaAs are studied at several doping levels and hole compensations, using a real-space Hamiltonian on an fcc lattice that reproduces the valence bands of undoped GaAs. Large-scale Monte Carlo (MC) simulations on a Cray XT3 supercomputer, using up to a thousand nodes, were needed to make this effort possible. Our analysis considers both the spin-orbit interaction and the random distribution of the Mn ions. The hopping amplitudes are functions of the GaAs Luttinger parameters. At the coupling J∼1.2 eV deduced from photoemission experiments, the MC Curie temperature and the shape of the magnetization curves are in agreement with experimental results for annealed samples. Although there are sizable differences with mean-field predictions, the system is found to be closer to a hole-fluid regime than to localized carriers.

Temperature-dependent resistivity of ferromagneticGa1−xMnxAs: Interplay between impurity scattering and many-body effects

“…For more heavily doped, high-T c metallic samples there are strong indications that the impurity band merges with the host semiconductor valence band forming mostly hostlike states at the Fermi energy with some low-energy tail of disorder-related localized states. 4 First-principles calculations [5][6][7] have so far not been fully conclusive regarding the nature of the itinerant carriers in this regime and further theoretical studies continue to be necessary. The question is thus, in essence, whether the valence-band 8 or impurity-band 9 picture is more adequate to describe the spectrum of experimental observations in Ga 1−x Mn x As.…”

Effective Heisenberg exchange integrals of diluted magnetic semiconductors determined within realistic multi-band tight-binding models

“…One possibility is to set up the hamiltonian for the full atomistic lattice and use s, p, d-orbitals because the chemical bond of GaAs is sp 3 -hybridized and the Mn 2+ impurities under consideration introduce d-orbitals into the problem. These kinds of approaches were already studied in the work of Tang and Flatté [15] [10], while the second one uses the sp 3 -basis as first suggested by Loehr in Ref. [18] and was also applied to ferromagnetic semiconductor superlattices [19].…”

“…A similar model was also used in recent Monte-Carlo (MC) simulations [10]. However, in this previous work only the three valence bands (per spin direction) of GaAs were taken into account, furthermore the Vterm was completely neglected and the whole investigation was restricted to relatively small systems.…”

“…We consider both, a six-band model (i.e. only the three valence bands per spin direction as investigated in [10]) and a more realistic eightband model (including also one conduction band). We take into account a finite concentration x of Mn-ions, which provide for a local impurity potential V , a local exchange coupling J pd and simultaneously serve as dopants (acceptors), and treat the disorder exactly.…”

Transport and optical conductivity in dilute magnetic semiconductors

“…Firstprinciples calculations [9,10] have not been fully conclusive regarding the nature of the itinerant carriers. Therefore, a lot of attention is being paid to effective Hamiltonian models [11,12] (whether based on the host band structures or impurity bands) or Monte Carlo simulations [13] and their abilities to adequately describe the experimental results.…”