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1.
An investigation is reported of stimulated two-photon emission by Bose-condensed excitons accompanied by a coherent two-exciton
recombination, i.e., by simultaneous recombination of two excitons with opposite momenta leaving unchanged the occupation
numbers of exciton states with momenta p≠0. Raman light scattering (RLS) accompanied by a similar two-exciton recombination (or production of two excitons) is also
analyzed. The processes under consideration can occur only if a system contains Bose condensate, so their detection can be
used as a new method to reveal Bose condensation of excitons. The recoil momentum, which corresponds to a change in the momentum
of the electromagnetic field in the processes, is transferred to phonons or impurities. If the recoil momentum is transmitted
to optical phonons with frequency ω
0
s
, whose occupation numbers are negligible, and the incident light frequency satisfies ω<2Ω, where Ω_=Ω−ω
0
s
is the difference frequency and Ω is the light frequency corresponding to the recombination of an exciton with zero momentum,
stimulated two-photon emission and RLS with coherent two-exciton recombination give rise to a line at 2Ω_ −ω and an anti-Stokes component at ω+2Ω_, respectively. For ω2Ω_ the RLS spectrum contains Stokes and anti-Stokes components at frequencies ω±2Ω_, whereas stimulated two-photon emission is impossible. Formulas for the cross sections at finite temperatures are obtained
for the processes under consideration. Our estimates indicate that a spectral line at 2Ω_−ω, corresponding to the stimulated two-photon emission accompanied by coherent optical phonon-assisted two-exciton recombination
can be experimentally detected in Cu2O.
Zh. éksp. Teor. Fiz. 115, 1353–1376 (April 1999) 相似文献
2.
The Zeeman splitting of the ground states 1s(hh) and 1s(lh) of excitons with heavy and light holes, respectively, in a 15-nm isolated Al0.3Ga0.7As/GaAs quantum well in magnetic fields of up to 20 T is investigated according to the photoluminescence excitation spectra
in the Faraday geometry (σ+− σ− components). The observed anomalous pattern of nonlinear Zeeman splitting and the nonmonotonic behavior of the effective
hole g factor are interpreted in terms of the strong mixing of the magnetoexcitonic states containing light and heavy holes.
Pis'ma Zh. éksp. Teor. Fiz. 64, No. 1, 52–56 (10 July 1996) 相似文献
3.
It is shown that the anharmonicity of crystal lattice vibrations in light metals such as beryllium, can give rise to a Fermi
resonance of optical one-phonon and acoustic two-phonon vibrations. New hybridized vibrational states are formed as a result
of such a resonance interaction: biphonon and quasibiphonon vibrations and renormalized optical vibrations. Depending on the
wave vector, these vibrational states can be both damped and stationary. The corresponding dispersion equation is obtained,
whose solution made it possible to determine the spectrum of these vibrations (dispersion curves and the wave vector dependence
of the damping for damped vibrations). It is shown that ultrafast damping of optical vibrations, similar to the well-known
superradiance effect for Frenkel’ and Wannier-Mott excitons, is possible.
Fiz. Tverd. Tela (St. Petersburg) 39, 542–546 (March 1997) 相似文献
4.
R. I. Dzhioev B. P. Zakharchenya V. L. Korenev P. E. Pak D. A. Vinokurov O. V. Kovalenkov I. S. Tarasov 《Physics of the Solid State》1998,40(9):1587-1593
Spin splitting of optically active and inactive excitons in nanosized n-InP/InGaP islands has been revealed. Optically inactive states become manifest in polarized-luminescence spectra as a result
of excitons being bound to neutral donors (or of the formation of the trion, a negatively charged exciton) in InP islands.
The exchange-splitting energies of the optically active and inactive states have been determined.
Fiz. Tverd. Tela (St. Petersburg) 40, 1745–1752 (September 1998) 相似文献
5.
K. L. Litvinenko I. Okhrimenko K. Köhler V. G. Lysenko K. Leo F. Löser 《JETP Letters》1998,67(10):869-874
The variation of the spectral shape of the four-wave mixing signal in GaAs/AlGaAs superlattices was studied experimentally
and theoretically. It was shown that in an external electric field, leading to anti-crossing of the levels of heavy and light
excitons, sawtooth oscillations of the energy position of the levels are observed. These oscillations are due to the inhomogeneous
broadening of the states participating in the Bloch oscillations.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 820–825 (25 May 1998) 相似文献
6.
V. A. Kosobukin 《Physics of the Solid State》1998,40(5):758-760
A theory of light absorption by excitons in periodic structures with an arbitrary number of quantum wells is constructed.
It is shown that the temperature dependence of the frequency-integrated absorption characteristics is due to a competition
between the processes of dissipative decay of quasi-two-dimensional excitons and the light-exciton interaction.
Fiz. Tverd. Tela (St. Petersburg) 40, 824–826 (May 1998) 相似文献
7.
J. Madrigal-Melchor F. Pérez-Rodríguez A. Silva-Castillo H. Azucena-Coyotécatl 《Physics of the Solid State》1998,40(5):796-797
The interaction of excitons with rough surfaces and its effect on light scattering spectra were investigated theoretically.
We have employed a model for the excitonic surface potential based upon the generalized Morse potential, taking into account
its random fluctuations produced by the surface roughness. Applying first-order perturbation theory, we calculate the cross
section of light scattering from a rough GaAs surface and analyze its frequency dependence in the presence of an extrinsic
surface-potential well with excitonic bound states.
Fiz. Tverd. Tela (St. Petersburg) 40, 865–866 (May 1998)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
8.
E. A. Mulyarov N. N. Sibel’din M. L. Skorikov V. A. Tsvetkov B. Etienne 《JETP Letters》1999,70(9):621-627
Lines corresponding to localized excitonic states formed from “above-barrier” electron and/or hole states (specifically, excitation
lines of excitons formed by an electron localized in a QW and a free heavy hole) have been observed in the photoluminescence
excitation spectra of GaAs/Al0.05Ga0.95As structures with quantum wells (QWs), each containing one single-particle size-quantization level for charge carriers of
each type. A computational method is proposed that permits finding the binding energy and wave functions of excitons in QWs
taking the Coulomb potential into account self-consistently. The computed values of the excitonic transition energies agree
quite well with the experimental results.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 9, 613–619 (10 November 1999) 相似文献
9.
R. I. Dzhioev B. P. Zakharchenya V. L. Korenev M. V. Lazarev 《Physics of the Solid State》1999,41(12):2014-2019
Magnetic interaction between spin-polarized nuclei and optically oriented excitons in a self-organized ensemble of size-quantized
InP islands in an InGaP matrix has been studied in a magnetic field in Faraday geometry. The effective magnetic fields generated
by polarized nuclei at excitons have been measured. The strengths of these fields were found to be different for active and
inactive excitons because of the difference between the excitonic g factors. The heavy-hole g factor has been determined. The active and inactive excitonic states were found to be coupled through cross-relaxation.
Fiz. Tverd. Tela (St. Petersburg) 41, 2193–2199 (December 1999) 相似文献
10.
V. B. Timofeev A. I. Tartakovskii A. I. Filin D. Birkedal J. Hvam 《Physics of the Solid State》1998,40(5):767-769
Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and
spatially indirect excitons in GaAs/AlGaAs superlattices having different electron and hole miniband widths in high magnetic
fields perpendicular to the heterolayers. The ground state of the indirect excitons formed by electrons and holes which are
spatially distributed among neighboring quantum wells is found to lie between the ground 1s state of the direct excitons and the threshold of the continuum of dissociated exciton states in the minibands. The indirect
excitons have a substantial oscillator strength when the binding energy of the exciton exceeds the scale of the width of the
resulting miniband. It is shown that a high magnetic field shifts a system of symmetrically bound quantum wells toward weaker
bonding. At high exciton concentrations, spatially indirect excitons are converted into direct excitons through exciton-exciton
collisions.
Fiz. Tverd. Tela (St. Petersburg) 40, 833–836 (May 1998) 相似文献
11.
V. L. Korenev 《JETP Letters》1999,70(2):129-134
A mechanism of dynamic self-polarization of nuclei is studied which is weakly temperature-dependent and operates efficiently
in low-dimensional systems (quantum wells, quantum dots). It is due to the hyperfine interaction of nuclei with excitons whose
spin polarization is artificially maintained at zero (by illuminating with unpolarized light) but for which nonequilibrium
alignment occurs. Nuclear self-polarization arises as a result of the conversion of the alignment of excitons into nuclear
orientation in the effective magnetic field of the polarized nuclei.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 124–129 (25 July 1999) 相似文献
12.
An analysis is made of the exciton angular-momentum alignment along a fluctuation in local magnetization, which is the first
stage in evolution of the localized-exciton spin state in a semimagnetic semiconductor. It is shown that spin relaxation of
localized excitons subjected to resonant optical excitation is accompanied by their relaxation in energy. When excited by
polarized light, this process gives rise to an anisotropic angular-momentum distribution in the spectrum of final exciton
states and, hence, to polarization of the secondary luminescence. Luminescence spectra of a cubic crystal are calculated,
and the possibility of their experimental observation discussed.
Fiz. Tverd. Tela (St. Petersburg) 40, 2156–2160 (December 1998) 相似文献
13.
Optical-resonance-Raman scattering by acoustic phonons is used to study the effect of an electric field on the state of excitons
in GaAs/AlAs superlattices. When the energy of the exciting photon coincides with the energy of an exciton bound to Wannier-Stark
states of a heavy hole and electron with Δn=0,±1, the acoustic Raman scattering is enhanced. Oscillations in the intensity of the Raman spectrum in the electric field
are explained by resonance delocalization of the exciton ground state as it interacts with Wannier-Stark states of neighboring
quantum wells or with Wannier-Stark states of a higher electron miniband.
Fiz. Tverd. Tela (St. Petersburg) 40, 827–829 (May 1998) 相似文献
14.
V. A. Kosobukin 《Physics of the Solid State》1998,40(2):332-335
The propagation of exciton polaritons in an optical waveguide with a quantum well is studied. Spatial dispersion of the excitons
causes the wave vector of the exciton polaritons to split between waveguide and exciton modes at resonance. The magnitude
of this splitting is determined by the radiative decay parameter of excitons with corresponding polarization in the quantum
well. The group velocity of the waveguide exciton polaritons in the resonance region can be three or four orders of magnitude
lower than the speed of light in vacuum.
Fiz. Tverd. Tela (St. Petersburg) 40, 362–365 (February 1998) 相似文献
15.
The ratio of the densities of intra-and interwell excitons in a symmetric system of coupled quantum wells — a superlattice
based on a GaAs/AlGaAs heterostructure — is investigated over a wide range of optical excitation power densities. Conversion
of interwell excitons into intrawell excitons as a result of exciton-exciton collisions is observed at high exciton densities.
Direct evidence for such a conversion mechanism is the square-root dependence of the interwell exciton density on the optical
excitation level. The decrease in the lifetime of interwell excitons with increasing excitation density, as measured directly
by time-resolved spectroscopy methods, confirms the explanation proposed for the effect.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 623–628 (25 April 1997) 相似文献
16.
We discuss drag effects in a two-layer system of spatially separated electrons and excitons: the entrainment of excitons by
moving electrons, and the entrainment of electrons by moving excitons. For the case of excitons entrained by electrons we
find the drag velocity υ
drag, and for electrons entrained by excitons we compute the induced electric field E
2. These drag effects can be sensitive indicators of the phase state of the excitons and of phase transitions in the exciton
system (to a liquid phase, superfluid state, etc.)
Zh. éksp. Teor. Fiz. 111, 1107–1119 (March 1997) 相似文献
17.
A. I. Tartakovskii V. B. Timofeev V. G. Lysenko D. Birkedal J. Hvam 《Journal of Experimental and Theoretical Physics》1997,85(3):601-608
Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and
spatially indirect excitons in GaAs/AlaAs superlattices, with different widths of the electron and hole minibands, located
in a high magnetic field perpendicular to the heterolayers. It is found that the ground state of the indirect excitons formed
by electrons and holes and spatially separated between neighboring quantum wells lies between the ls ground state of the direct excitons and the continuum threshold for dissociated exciton states in the minibands. Indirect
excitons in superlattices have a significant oscillator strength when the binding energy of the exciton exceeds the order
of the width of the resulting miniband. The behavior of the binding energy of direct and indirect heavy hole excitons during
changes in the tunneling coupling between the quantum wells is established. It is shown that a strong magnetic field, which
intensifies the Coulomb interaction between the electron and hole in an exciton, weakens the bond in a system of symmetrically
bound quantum wells. The spatially indirect excitons studied here are analogous to first order Wannier-Stark localized excitons
in superlattices with inclined bands (when an electrical bias is applied), but in the present case the localization is of
purely Coulomb origin.
Zh. éksp. Teor. Fiz. 112, 1106–1118 (September 1997) 相似文献
18.
A. V. Bazhenov A. V. Gorbunov M. Yu. Maksimuk T. N. Fursova 《Journal of Experimental and Theoretical Physics》1997,85(1):135-140
Spectra of photoinduced light absorption in C60 films at high and low excitations in the temperature range between 15 and 300 K have been measured. In addition to the well-known
explanation of photoinduced absorption in terms of optical transitions in the system of photogenerated singlet excitons, triplet
excitons, and polarons, changes in the absorption spectrum of the fullerite ground state must be considered. We suggest taking
into account the effect of crystal field in explaining the features of the photoinduced absorption spectrum. A feature similar
to the inverted luminescence spectrum and ascribed to optical excitation of singlet excitons, which is partially allowed owing
to intermolecular interaction, has been detected in spectrum of photoinduced absorption.
Zh. éksp. Teor. Fiz. 112, 246–256 (July 1997) 相似文献
19.
V. M. Agranovich S. A. Kiselev Z. G. Soos S. R. Forrest 《Physics of the Solid State》1999,41(5):704-707
We discuss the phase transition to the conducting state in a system of 2D charge-transfer excitons (CTEs) at a donor-acceptor interface. The phase transition arises due to strong dipole-dipole repulsion
between CTEs which stimulates the population of free carriers in higher energy states even at low temperature. We use the
computer simulations with the random distribution of excitons, with finite lifetime explicitly taken into account. The critical
concentration of CTEs and their energy distribution are calculated. We also discuss the possibility of observing the predicted
phenomena.
Fiz. Tverd. Tela (St. Petersburg) 41, 781–784 (May 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
20.
D. B. Turchinovich V. P. Kochereshko D. R. Yakovlev W. Ossau G. Landwehr T. Wojtowicz G. Karczewski J. Kossut 《Physics of the Solid State》1998,40(5):747-749
A study has been made of bound exciton-electron complexes (trions) and unbound exciton-electron states (combined exciton-cyclotron
resonance) from reflectance spectra obtained from modulation-doped CdTe/CdMgTe quantum-well structures. It has been established
that the contribution of trions to dielectric permittivity is comparable to that of excitons. An analysis is made of the magnetic-field
dependence of the parameters describing the contribution to dielectric permittivity due to exciton-cyclotron-resonance states.
Fiz. Tverd. Tela (St. Petersburg) 40, 813–815 (May 1998) 相似文献