The optical exciton Aharonov-Bohm effect, i. e. an oscillatory component in the energy of optically active (bright) states, is investigated in nanorings. It is shown that a small effective electron mass, strong confinement of the electron, and high barrier for the hole, achieved e. g. by an InAs nanoring embedded in an AlGaSb quantum well, are favorable for observing the optical exciton Aharonov-Bohm effect. The second derivative of the exciton energy with respect to the magnetic field is utilized to extract Aharonov-Bohm oscillations even for the lowest bright state unambiguously. A connection between the theories for infinitesimal narrow and finite width rings is established. Furthermore, the magnetization is compared to the persistent current, which oscillates periodically with the magnetic field and confirms thus the non-trivial (connected) topology of the wave function in the nanoring.
We investigate the interaction of excitons in a two dimensional lattice and
photons in a planar cavity in the presence of disorder. The strong
exciton-photon coupling is described in terms of polariton quasi-particles,
which are scattered by a disorder potential. We consider three kinds of
disorder: (a) inhomogeneous exciton energy, (b) inhomogeneous exciton-photon
coupling and (c) deviations from an ideal lattice. These three types of
disorder are characteristic of different physical systems, and their separate
analysis gives insight on the competition between randomness and light-matter
coupling. We consider conventional planar polariton structures (with excitons
resonant to photon modes emitting normal to the cavity) and Bragg polariton
structures, in which excitons in a lattice are resonant with photon modes at a
finite angle satisfying the Bragg condition. We calculate the absorption
spectra in the normal direction and at the Bragg angle by a direct
diagonalization of the exciton-photon Hamiltonian. We found that in some cases
weak disorder increases the light-matter coupling and leads to a larger
polariton splitting. Moreover, we found that the coupling of excitons and
photons is less sensitive to disorder of type (b) and (c). This suggests that
polaritonic structures realized with impurities in a semiconductor or with
atoms in optical lattices are good candidate for the observation of some of the
Bragg polariton features.Comment: 8 pages, 5 figure
The exciton-polariton modes of a quantum dot lattice embedded in a planar
optical cavity are theoretically investigated. Umklapp terms, in which an
exciton interacts with many cavity modes differing by reciprocal lattice
vectors, appear in the Hamiltonian due to the periodicity of the dot lattice.
We focus on Bragg polariton modes obtained by tuning the exciton and the cavity
modes into resonance at high symmetry points of the Brillouin Zone. Depending
on the microcavity design these polaritons modes at finite in-plane momentum
can be guided and can have long lifetimes. Moreover, their effective mass can
be extremely small, of the order of $10^{-8} m_0$ ($m_0$ is the bare electron
mass), and they constitute the lightest exciton-like quasi-particles in solids.Comment: 10 pages and 7 figure
Absorption spectra and wave functions of optically active exciton states in disordered quantum wells are calculated. The interplay between the relative and center-of-mass part of the total exciton wave function is investigated using a perpendicular magnetic field. The diamagnetic shift varies strongly in correspondence with the wave function localization. The full solution reveals failures of the simple factorization in relative and center-of-mass coordinates even for weak global disorder.
A combined study of the optical and structural properties of AlGaAs/ GaAs quantum wells is presented. Microphotoluminescence experiments, magnetomicrophotoluminescence, and atomically resolved crosssectional scanning tunneling microscopy were performed on the same quantum well sample. Constant-current topographs with aluminum and/or gallium sensitivity are used to directly extract disorder potentials. Using these potentials, exciton absorption spectra, microphotoluminescence spectra, and diamagnetic shifts of individual exciton states are calculated in an envelope function approximation. Very good agreement between the theoretical and experimental results is found.
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