212 research outputs found
Cubic anisotropy of hole Zeeman splitting in semiconductor nanocrystals
We study theoretically cubic anisotropy of Zeeman splitting of a hole
localized in semiconductor nanocrystal. This anisotropy originates from three
contributions: crystallographic cubically-symmetric spin and kinetic energy
terms in the bulk Luttinger Hamiltonian and the spatial wave function
distribution in a cube-shaped nanocrystal. From symmetry considerations, an
effective Zeeman Hamiltonian for the hole lowest even state is introduced,
containing a spherically symmetric and a cubically symmetric term. The values
of these terms are calculated numerically for spherical and cube-shaped
nanocrystals as functions of the Luttinger Hamiltonian parameters. We
demonstrate that the cubic shape of the nanocrystal and the cubic anisotropy of
hole kinetic energy (so called valence band warping) significantly affect
effective factors of hole states. In both cases, the effect comes from the
cubic symmetry of the hole wave functions in zero magnetic field. Estimations
for the effective factor values in several semiconductors with zinc-blende
crystal lattices are made. Possible experimental manifestations and potential
methods of measurement of the cubic anisotropy of the hole Zeeman splitting are
suggested.Comment: 17 pages, 7 figure
Quantum Oscillations of Photocurrents in HgTe Quantum Wells with Dirac and Parabolic Dispersions
We report on the observation of magneto-oscillations of terahertz radiation
induced photocurrent in HgTe/HgCdTe quantum wells (QWs) of different widths,
which are characterized by a Dirac-like, inverted and normal parabolic band
structure. The photocurrent data are accompanied by measurements of
photoresistance (photoconductivity), radiation transmission, as well as
magneto-transport. We develop a microscopic model of a cyclotron-resonance
assisted photogalvanic effect, which describes main experimental findings. We
demonstrate that the quantum oscillations of the photocurrent are caused by the
crossing of Fermi level by Landau levels resulting in the oscillations of spin
polarization and electron mobilities in spin subbands. Theory explains a
photocurrent direction reversal with the variation of magnetic field observed
in experiment. We describe the photoconductivity oscillations related with the
thermal suppression of the Shubnikov-de Haas effect.Comment: 16 pages, 13 figure
Statistics of excitons in quantum dots and the resulting microcavity emission spectra
A theoretical investigation is presented of the statistics of excitons in
quantum dots (QDs) of different sizes. A formalism is developed to build the
exciton creation operator in a dot from the single exciton wavefunction and it
is shown how this operator evolves from purely fermionic, in case of a small
QD, to purely bosonic, in case of large QDs. Nonlinear optical emission spectra
of semiconductor microcavities containing single QDs are found to exhibit a
peculiar multiplet structure which reduces to Mollow triplet and Rabi doublet
in fermionic and bosonic limits, respectively.Comment: Extensively expanded revision, 14 pages, 12 figures, submitted to
Phys. Rev.
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