949 research outputs found
Theory of resonant Raman scattering due to spin-flips of resident charge carries and excitons in perovskite semiconductors
We have developed a theory of Raman scattering with single and double spin
flips of localized resident electrons and holes as well as nonequilibrium
localized excitons in semiconductor perovskite crystals under optical
excitation in the resonant exciton region. Scattering mechanisms involving
localized excitons, biexcitons and exciton polaritons as intermediate states
has been examined, the spin-flip Raman scattering by polaritons being a novel
mechanism. The derived equations are presented in the invariant form allowing
one for the analysis of the dependence of scattering efficiency on the
polarization of the initial and scattered light and on the orientation of the
external magnetic field.Comment: 15 pages, 2 figures, 2 table
Theory of acceptor-ground-state description and hot photoluminescence in cubic semiconductors
An approach to the theory of the acceptor ground state in cubic semiconductors is presented. The model has been developed within the framework of the four-band effective Luttinger Hamiltonian and is applicable for both Coulomb and non-Coulomb accepters. The system of integral equations for the ground-state wave functions has been derived and its solution has been numerically computed. We present the general form of the acceptor-ground-state wave function. The wave functions for a set of acceptor dopants in GaAs are calculated with an accuracy of 2%. The obtained wave functions have been used for qualitative and quantitative analysis of the hot photoluminescence (HPL) spectra and linear polarization in GaAs crystals. Analytical expressions for the line shape and anisotropy of the linear polarization degree have been derived. The dependencies of the HPL characteristics on the excitation energy as well as on the acceptor binding energy have been analyzed. The HPL theory presented allows us to describe the wide spectrum of available experimental data
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
Exciton spin dynamics and photoluminescence polarization of CdSe/CdS dot-in-rod nanocrystals in high magnetic fields
The exciton spin dynamics and polarization properties of the related emission
are investigated in colloidal CdSe/CdS dot-in-rod (DiR) and spherical
core/shell nanocrystal (NC) ensembles by magneto-optical photoluminescence (PL)
spectroscopy in magnetic fields up to 15 T. It is shown that the degree of
circular polarization (DCP) of the exciton emission induced by the magnetic
field is affected by the NC geometry as well as the exciton fine structure and
can provide information on nanorod orientation. A theory to describe the
circular and linear polarization properties of the NC emission in magnetic
field is developed. It takes into account phonon mediated coupling between the
exciton fine structure states as well as the dielectric enhancement effect
resulting from the anisotropic shell of DiR NCs. This theoretical approach is
used to model the experimental results and allows us to explain most of the
measured features. The spin dynamics of the dark excitons is investigated in
magnetic fields by time-resolved photoluminescence. The results highlight the
importance of confined acoustic phonons in the spin relaxation of dark
excitons. The bare core surface as well as the core/shell interface give rise
to an efficient spin relaxation channel, while the surface of core/shell NCs
seems to play only a minor role.Comment: 18 pages, 15 figure
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