163 research outputs found
Double-exciton component of the cyclotron spin-flip mode in a quantum Hall ferromagnet
We report on the calculation of the cyclotron spin-flip excitation (CSFE) in
a spin-polarized quantum Hall system at unit filling. This mode has a
double-exciton component which contributes to the CSFE correlation energy but
can not be found by means of a mean field approach. The result is compared with
available experimental data.Comment: 9 pages, 2 figure
Charged two-dimensional magnetoexciton and two-mode squeezed vacuum states
A novel unitary transformation of the Hamiltonian that allows one to
partially separate the center-of-mass motion for charged electron-hole systems
in a magnetic field is presented. The two-mode squeezed oscillator states that
appear at the intermediate stage of the transformation are used for
constructing a trial wave function of a two-dimensional (2D) charged
magnetoexciton.Comment: 9 pages, 1 figur
Charged mobile complexes in magnetic fields: A novel selection rule for magneto-optical transitions
The implications of magnetic translations for internal optical transitions of
charged mobile electron-hole (--) complexes and ions in a uniform
magnetic field are discussed. It is shown that transitions of such
complexes are governed by a novel exact selection rule. Internal intraband
transitions of two-dimensional (2D) charged excitons in strong magnetic
fields are considered as an illustrative example.Comment: 4 pages, 2 figure
Two-dimensional magnetoexcitons in the presence of spin-orbit coupling
We study theoretically the effect of spin-orbit coupling on quantum well
excitons in a strong magnetic field. We show that, in the presence of an
in-plane field component, the excitonic absorption spectrum develops a
double-peak structure due to hybridization of bright and dark magnetoexcitons.
If the Rashba and Dresselhaus spin-orbit constants are comparable, the
magnitude of splitting can be tuned in a wide interval by varying the azimuthal
angle of the in-plane field. We also show that the interplay between spin-orbit
and Coulomb interactions leads to an anisotropy of exciton energy dispersion in
the momentum plane. The results suggest a way for direct optical measurements
of spin-orbit parameters.Comment: 9 pages, 6 figure
Definitive observation of the dark triplet ground state of charged excitons in high magnetic fields
The ground state of negatively charged excitons (trions) in high magnetic
fields is shown to be a dark triplet state, confirming long-standing
theoretical predictions. Photoluminescence (PL), reflection, and PL excitation
spectroscopy of CdTe quantum wells reveal that the dark triplet trion has lower
energy than the singlet trion above 24 Tesla. The singlet-triplet crossover is
"hidden" (i.e., the spectral lines themselves do not cross due to different
Zeeman energies), but is confirmed by temperature-dependent PL above and below
24 T. The data also show two bright triplet states.Comment: 4 figure
Charged hydrogenic problem in a magnetic field: Non-commutative translations, unitary transformations, and coherent states
An operator formalism is developed for a description of charged electron-hole
complexes in magnetic fields. A novel unitary transformation of the Hamiltonian
that allows one to partially separate the center-of-mass and internal motions
is proposed. We study the operator algebra that leads to the appearance of new
effective particles, electrons and holes with modified interparticle
interactions, and their coherent states in magnetic fields. The developed
formalism is used for studying a two-dimensional negatively charged
magnetoexciton . It is shown that Fano-resonances are present in the
spectra of internal transitions, indicating the existence of
three-particle quasi-bound states embedded in the continuum of higher Landau
levels.Comment: 9 pages + 2 figures, accepted in PRB, a couple of typos correcte
Spin Relaxation in a Quantized Hall Regime in Presence of a Disorder
We study the spin relaxation (SR) of a two-dimensional electron gas (2DEG) in
the quantized Hall regime and discuss the role of spatial inhomogeneity effects
on the relaxation. The results are obtained for small filling factors () or when the filling factor is close to an integer. In either case SR times
are essentially determined by a smooth random potential. For small we
predict a "magneto-confinement" resonance manifested in the enhancement of the
SR rate when the Zeeman energy is close to the spacing of confinement sublevels
in the low-energy wing of the disorder-broadened Landau level. In the resonant
region the -dependence of the SR time has a peculiar non-monotonic shape. If
, the SR is going non-exponentially. Under typical conditions
the calculated SR times range from to s.Comment: 10 pages, 1 figure. To appear in JETP Letter
Internal transitions of quasi-2D charged magneto-excitons in the presence of purposely introduced weak lateral potential energy variations
Optically detected resonance spectroscopy has been used to investigate
effects of weak random lateral potential energy fluctuations on internal
transitions of charged magneto-excitons (trions) in quasi two-dimensional
GaAs/AlGaAs quantum-well (QW) structures. Resonant changes in the ensemble
photoluminescence induced by far-infrared radiation were studied as a function
of magnetic field for samples having: 1) no growth interrupts (short range
well-width fluctuations), and 2) intentional growth interrupts (long range
monolayer well-width differences). Only bound-to-continuum internal transitions
of the negatively charged trion are observed for samples of type 1. In
contrast, a feature on the high field (low energy) side of electron cyclotron
resonance is seen for samples of type 2 with well widths of 14.1 and 8.4 nm.
This feature is attributed to a bound-to-bound transition of the spin-triplet
with non-zero oscillator strength resulting from breaking of translational
symmetry.Comment: 16 pages, 3 figures, submitted to Physical Review
Goldstone Mode Relaxation in a Quantum Hall Ferromagnet due to Hyperfine Interaction with Nuclei
Spin relaxation in quantum Hall ferromagnet regimes is studied. As the
initial non-equilibrium state, a coherent deviation of the spin system from the
direction is considered and the breakdown of this Goldstone-mode
state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring
non-exponentially with time is studied in terms of annihilation processes in
the "Goldstone condensate" formed by "zero spin excitons". The relaxation rate
is calculated analytically even if the initial deviation is not small. This
relaxation channel competes with the relaxation mechanisms due to spin-orbit
coupling, and at strong magnetic fields it becomes dominating.Comment: 8 page
- …