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The coupling of an electron gas confined by a harmonic potential and submitted to a strong magnetic field tilted in relation to the confining direction creates an excitation called here magneto-polariton. This work describes the origin of this excitation and calculates the energy eigenvalues for different tilted angles. It presents the reasons leading to the crossings and repulsions of the energy bands, the degeneracy of the states, the way the Fermi levels change with the magnetic field, the influence of an external electric field, and how the Hall resistance plateaus change with the change in the tilted angle. [ABSTRACT FROM AUTHOR]

We investigate the spin-polarized transport of holes in GaMnAs/GaAs heterostructures with Mn concentration 5% in which a ferromagnetic order is known to exist. Disorder enters the problem both in the random distribution of Mn centers and impurities, and also in the orientation of the magnetic moments at the Mn sites. We take into account the existence of an impurity band determining the extended or localized nature of the states at and near the Fermi level. Magnetic order and resistivity are inter-related due to the influence of the spin polarization of the impurity band and the effect of the Zeeman splitting on the mobility edge. We obtain two channels of transport, one provided by the extended states above the mobility edge, when this lies below the Fermi level, the other coming out of the thermal excitation of the localized states through a hopping mechanism. We discuss the competition between these two channels in determining, once having obtained the dependence of the resistance on temperature, the metallic or non-metallic nature of the sample. [ABSTRACT FROM AUTHOR]

The interplay between disorder and spin polarization in a GaMnAs thin layer results into spin-polarized impurity hole bands. A figure of merit is defined to label the nature of the sample as metallic or nonmetallic. It is shown that samples with the highest figures of merit have a ratio between the extended hole density and the Mn concentration near 0.2, in agreement with the ratio of 0.1–0.25 known to occur among samples produced with the highest Curie temperatures. Both the nonmetal-to-metal and the metal-to-nonmetal transitions experimentally observed in the ferromagnetic regime are obtained as the Mn concentration increases. [ABSTRACT FROM AUTHOR]

A self-consistent calculation of the density of states and the spectral density function is performed in a two-dimensional spin-polarized hole system based on a multiple-scattering approximation. Using parameters corresponding to GaMnAs thin layers, a wide range of Mn concentrations and hole densities have been explored to understand the nature, localized or extended, of the spin-polarized holes at the Fermi level for several values of the average magnetization of the Mn system. The authors show that, for a certain interval of Mn and hole densities, an increase on the magnetic order of the Mn ions come together with a change of the nature of the states at the Fermi level. This fact provides a delocalization of spin-polarized extended states antialigned to the average Mn magnetization and a higher spin polarization of the hole gas. This nonmetal-to-metal transition caused by the increase of Mn concentration once the ferromagnetic phase is reached was observed experimentally since the first samples were produced. These results are consistent with the occurrence of ferromagnetism with relatively high transition temperatures observed in some thin film samples and multilayered structures of this material. [ABSTRACT FROM AUTHOR]