454 research outputs found
Ferromagnetic ordering in dilute magnetic dielectrics with and without free carriers
The state of art in the theoretical and experimental studies of transition
metal doped oxides (dilute magnetic dielectrics) is reviewed. The available
data show that the generic non-equilibrium state of oxide films doped with
magnetic impurities may either favor ferromagnetism with high Curie temperature
or result in highly inhomogeneous state without long-range magnetic order. In
both case concomitant defects (vacancies, interstitial ions play crucial part.Comment: 10 pages, 3 figures. The paper was presented at the Moscow
Internation Symposium on Magnetism (MISM-08). To be published in Journ.
Magnetism and Magnetic Material
Many-particle resonances in excited states of semiconductor quantum dots
Anderson impurity model for semiconductor quantum dot is extended to take
into account both particle and hole branches of charge excitations. It is shown
that in dots with even number of electrons where the Kondo effect is absent in
the ground state, novel midgap exciton states emerge in the energy spectrum due
to Kondo-type shake-up processes. The relevance of the model to
heterostructures doped by transition metal impurities and to rare earth ions
adsorbed on metallic surfaces is discussed.Comment: 9 pages, 6 ps figure
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
Time-dependent single electron tunneling through a shuttling nano-island
We offer a general approach to calculation of single-electron tunneling
spectra and conductance of a shuttle oscillating between two half-metallic
leads with fully spin polarized carriers. In this case the spin-flip processes
are completely suppressed and the problem may be solved by means of canonical
transformation, where the adiabatic component of the tunnel transparency is
found exactly, whereas the non-adiabatic corrections can be taken into account
perturbatively. Time-dependent corrections to the tunnel conductance of moving
shuttle become noticeable at finite bias in the vicinity of the even/odd
occupation boundary at the Coulomb diamond diagram.Comment: 12 pages, 4 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.
Dynamical and point symmetry of the Kondo effect in triangular quantum dot
In this work we concentrate on the {\it point symmetry} of triangular triple
quantum dot and its interplay with the {\it spin rotation symmetry} in the
context of Kondo tunneling through this kind of artificial molecule.
A fully symmetric triangular triple quantum dot is considered, consisting of
three identical puddles with the same individual properties (energy levels and
Coulomb blockade parameters) and inter-dot coupling (tunnel amplitudes and
electrostatic interaction). The underlying Kondo physics is determined by the
product of a discrete rotation symmetry group in real space and a continuous
rotation symmetry in spin space. These symmetries are reflected in the
resulting exchange hamiltonian which naturally involves spin and orbital
degrees of freedom. The ensuing poor-man scaling equations are solved and the
Kondo temperature is calculated.Comment: 7 pages 1 figure, to appear in the proceeding of FQMT04 (Prague, July
2004
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