80 research outputs found
Collective excitations in a magnetically doped quantized Hall ferromagnet
A theory of collective states in a magnetically quantized two-dimensional
electron gas (2DEG) with half-filled Landau level (quantized Hall ferromagnet)
in the presence of magnetic 3d impurities is developed. The spectrum of bound
and delocalized spin-excitons as well as the renormalization of Zeeman
splitting of the impurity 3d levels due to the indirect exchange interaction
with the 2DEG are studied for the specific case of n-type GaAs doped with Mn
where the Lande` g-factors of impurity and 2DEG have opposite signs. If the
sign of the 2DEG g-factor is changed due to external influences, then impurity
related transitions to new ground state phases, presenting various spin-flip
and skyrmion-like textures, are possible. Conditions for existence of these
phases are discussed. PACS: 73.43.Lp, 73.21.Fg, 72.15.RnComment: 32 pages including 7 figures. To be published in Phys. Rev.
Classical and quantum radiation of perturbed discrete breathers
We show that the linearized phase space flow around a discrete breather
solution is not capable of generating persistent energy flow away from the
breather even in the case of instabilities of extended states. This holds both
for the classical and quantized description of the flow. The main reason for
that is the parametric driving the breather provides to the flow. Corresponding
scaling arguments are derived for both classical and quantum cases. Numerical
simulations of the classical flow support our findings.Comment: 8 pages, 3 figure
Spin-engineered quantum dots
Spatially nonhomogeneously spin polarized nuclei are proposed as a new
mechanism to monitor electron states in a nanostructure, or as a means to
createn and, if necessary, reshape such nanostructures in the course of the
experiment. We found that a polarization of nulear spins may lift the spin
polarization of the electron states in a nanostructure and, if sufficiently
strong, leads to a polarization of the electron spins. Polarized nuclear spins
may form an energy landscape capable of binding electrons with energy up to
several meV and the localization radius 100\AA.Comment: 9 pages, 1 figure, submitted to Physica E, Augist 31, 200
Double exchange mechanisms for Mn doped III-V ferromagnetic semiconductors
A microscopic model of indirect exchange interaction between transition metal
impurities in dilute magnetic semiconductors (DMS) is proposed. The
hybridization of the impurity d-electrons with the heavy hole band states is
largely responsible for the transfer of electrons between the impurities,
whereas Hund rule for the electron occupation of the impurity d-shells makes
the transfer spin selective. The model is applied to such systems as type
GaN:Mn and type (Ga,Mn)As, type (Ga,Mn)P. In type DMS with
Mn impurities the exchange mechanisms is rather close to the
kinematic exchange proposed by Zener for mixed-valence Mn ions. In type DMS
ferromagnetism is governed by the kinematic mechanism involving the kinetic
energy gain of heavy hole carriers caused by their hybridization with 3d
electrons of Mn impurities. Using the molecular field approximation the
Curie temperatures are calculated for several systems as functions of the
impurity and hole concentrations. Comparison with the available experimental
data shows a good agreement.Comment: Submitted to PR
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