# 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.

*Host: Harold Baranger*