138 research outputs found
Bound spin-excitons in two-dimensional electron gas
A theory of the spin exciton capture by a magnetic impurity in a 2D electron
gas is developed. We consider the resonance model for electron scattering by a
transition metal impurity and calculate the binding potential for spin
excitons. This potential is spin selective and is capable of binding a spin
exciton with zero angular momentum. In order to trap an exciton with a nonzero
angular momentum m, the potential must exceed a certain threshold value,
depending on m.Comment: 11 pages, 3 figure
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.
Condensation of Photons coupled to a Dicke Field in an Optical Microcavity
Motivated by recent experiments reporting Bose-Einstein condensation (BEC) of
light coupled to incoherent dye molecules in a microcavity, we show that due to
a dimensionality mismatch between the 2D cavity-photons and the 3D arrangement
of molecules, the relevant molecular degrees of freedom are collective Dicke
states rather than individual excitations. For sufficiently high dye
concentration the coupling of the Dicke states with light will dominate over
local decoherence. This system also shows Mott criticality despite the absence
of an underlying lattice in the limit when all dye molecules become excited.Comment: 4 pages + supplementary materia
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
- …