Condensed Matter Seminar Series

Title: Microscopic Hamiltonian for Diluted Magnetic Semiconductors

Adriana Moreo

Oak Ridge National Lab and University of Tennessee

Tuesday May 16,  11:30 am,  Room 298,  Physics Building

Abstract:  We formulated a real space Hamiltonian to study the effect of dilute magnetic doping of III-V semiconductors. A p-type valence band is considered and nearest neighbor hopping of holes among bonding orbitals in a diamond lattice is allowed. The relevant hopping parameters between orbitals are obtained in terms of the Luttinger parameters. Considering the effects of the spin-orbit interactions the number of degrees of freedom per site is reduced from 6 (3 orbitals and two spin orientations for the p bands) to 4 (the four projections corresponding to j=3/2 which is the quantum number of the heavy and light hole bands). The magnetic interaction between the doped magnetic impurities and the spin of the mobile holes is written in the appropriated base. The numerical values of the hopping parameters and Hund interaction are obtained from the literature for the different compounds and, thus, there are no free parameters. The properties of the materials are calculated using numerical techniques. The newly developed TPEM method allows us to consider lattices with NxNxN cubes with N as big as 6. Since there are 4 ions associated to each site of a cube in an fcc lattice the total number of Ga sites in our simulations is 4xNxNxN. Finite size effects are very small when systems larger than 3x3x3 cubes are considered. For Mn doped GaAs we reproduce the experimentally observed Curie temperatures for all the studied values of effective hole dopings. The accepted value for J=1.2eV corresponds to weak coupling since impurity bands above the top of the valence band are not observed. These bands form for much larger values of J. Results for other magnetically doped III-V compounds will be presented.