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1.
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
2.
A. N. Izotov V. V. Kveder Yu. A. Osip’yan É. A. Steinman R. K. Nikolaev N. S. Sidorov 《Journal of Experimental and Theoretical Physics》1998,87(6):1205-1213
The absorption coefficient of perfect single crystals of the fullerene C60 is measured in the energy range 1.6–2.1 eV at temperatures from 4.2 to 300 K. An absorption fine structure is discovered
in the and is assigned to electronic and vibronic transitions with the production of free excitons and excitons localized
on structural defects. It is shown that in the region of the structural phase transition from a face-centered cubic structure
to a simple cubic structure the absorption coefficient undergoes a jump, which is associated with an energy shift of the free
exciton line toward lower energies. It is discovered that spatial inhomogeneity, which is associated with the growth of the
new phase from a finite number of nuclei, appears in the crystal at the time of this transition.
Zh. éksp. Teor. Fiz. 114, 2211–2224 (December 1998) 相似文献
3.
Yu. E. Lozovik O. L. Berman M. Willander 《Journal of Experimental and Theoretical Physics》1999,88(5):980-986
Instability in a system of interacting quasi-two-dimensional excitons in a type II superlattice of a finite thickness due
to attraction between oppositely-directed excitonic dipoles in neighboring layers has been discovered. A stable system is
that of indirect quasi-two-dimensional biexcitons formed by indirect excitons with dipole moments oriented in opposite directions.
The radius and binding energy of indirect biexcitons has been calculated. A collective spectrum of a system of such biexcitons
with a weak quadrupole interaction between them has been studied. Feasibility of Bose condensation, the density n
s(T) of the superfluid component, and a phase transition to the superfliud state in a low-density system of indirect biexcitons
have been analyzed.
Zh. éksp. Teor. Fiz. 115, 1786–1798 (May 1999) 相似文献
4.
We show that large fluctuations of D-mesons kinetic-energy (or momentum) distributions might be a signature of a phase transition to the Quark-Gluon Plasma (QGP).
In particular, a jump in the variance of the momenta or kinetic energy, as a function of a control parameter (temperature
or Fermi energy at finite baryon densities) might be a signature for a first-order phase transition to the QGP. This behavior
is completely consistent with the order parameter defined for a system of interacting quarks both at zero temperature (and
finite baryon densities) or at finite temperatures which shows a jump in correspondence with a first-order phase transition
to the QGP. The J/Ψ displays exactly the same behavior of the order parameter and of the variance of the D-mesons. We discuss implications for relativistic heavy-ion collisions within the framework of a transport model and possible
hints for experimental search. 相似文献
5.
W. Ossau D. R. Yakovlev C. Y. Hu V. P. Kochereshko G. V. Astakhov R. A. Suris P. C. M. Christianen J. C. Maan 《Physics of the Solid State》1999,41(5):751-756
II–VI quantum-well structures containing a 2DEG of low density have been investigated by means of polarized photoluminescence,
photoluminescence excitation and reflectivity in external magnetic fields up to 20 T. The spin splittings of the exciton X and the negatively charged exciton X
− are measured as a function of the magnetic field strength. The behavior of the magnetic-field-induced polarization degree
of the luminescence line related to X
− demonstrates the formation process of negatively charged excitons from excitons and free carriers polarized by the external
magnetic field. We have determined the binding energies of the trion formed either with the heavy-hole or the light-hole exciton.
The optically detected magnetic resonance (ODMR) technique was applied for the first time to study the optical transition
processes in a nanosecond timescale. The electron ODMR was observed with the detection on either the direct exciton or the
negatively charged exciton X. Further evidence for the interaction of excitons with the electrons of the two-dimensional gas are demonstrated by a combined
exciton-cyclotron resonance line observed in reflectivity and luminescence excitation, shake-up processes observed in photoluminescence,
as well as inelastic and spin-dependent scattering processes.
Fiz. Tverd. Tela (St. Petersburg) 41, 831–836 (May 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
6.
We study the four dimensional (4D) ±J Ising spin glass in a magnetic field with the simulated tempering algorithm recently introduced by Marinari and Parisi. We compute numerically the order parameter function P(q) and analyze the temperature dependence of the first four cumulants of the distribution. We discuss the evidence in favor of the existence of a phase transition in a field. Assuming a well defined transition we are able to bound its critical temperature. 相似文献
7.
8.
We present theoretical calculations of the variation of exciton energies in truncated conical InGaN quantum dots (QDs) in a GaN matrix with dot size and indium composition. We compute the built-in strain-induced and spontaneous piezoelectric fields using a surface integral method that we have recently derived, and confirm that the built-in fields can be of the order of a few MV/cm, resulting in a spatial separation of the electrons and holes. The ground state wavefunctions of the exciton (X0), biexciton (2X0) and the two charged excitons (X− and X+) are then calculated in the Hartree approximation, using a self-consistent finite difference method. We find that the electron–hole recombination energy is always blue-shifted for the charged excitons X− and X+, with a further blue-shift for the biexciton, and this blue-shift increases with increasing indium content. We describe the trends in interband transition energy and the scale of the blue-shift with dot size, shape and composition. We conclude that spectroscopic studies of the exciton, charged excitons and biexciton should provide a useful probe of the structural and piezoelectric properties of GaN-based QDs. 相似文献
9.
A. N. Starukhin B. S. Razbirin A. V. Chugreev M. Happ F. Henneberger 《Physics of the Solid State》1999,41(8):1271-1274
The Zeeman effect in the emission spectra of localized excitons in semiconductor solid solutions has been studied by selective
laser spectroscopy. It was shown that the fine structure appearing in the emission spectra of GaSe1−x
Tex crystals under resonant monochromatic excitation in a magnetic field originates from spin relaxation of the light-induced
localized excitons between their Zeeman sublevels. The localized-exciton g factor and its dependence on the energy of localized-exciton formation and solid-solution composition has been measured.
Fiz. Tverd. Tela (St. Petersburg) 41, 1389–1393 (August 1999) 相似文献
10.
We predict that a phase transition in freestanding monolayer Xenes from the semiconducting phase to the excitonic insulating (EI) phase can be induced by reducing an external electric field below some critical value which is unique to each material. The splitting of the conduction and valence bands due to spin–orbit coupling at non-zero electric fields leads to the formation of A and B excitons in the larger or smaller band gap, with correspondingly larger or smaller binding energies. Our calculations show the coexistence of the semiconducting phase of A excitons with the EI phase of B excitons for a particular range of electric field. The dielectric environment precludes the existence of the EI phase in supported or encapsulated monolayer Xenes. 相似文献
11.
A. A. Rogachev 《Physics of the Solid State》1998,40(5):855-857
Excitons in many-valley semiconductors form molecules consisting of four and more excitons. The degeneracy factor g of the conduction band in germanium is 8, and in silicon g=12. As in acceptors, the hole ground state in excitons is fourfold degenerate. The same is valid for exciton molecules, because
they are quantum objects with spherical symmetry. The exciton binding energy in molecules is close to that in exciton-liquid
droplets. Experimental evidence is considered for the existence, besides biexcitons, of stable exciton molecules consisting
of three and four, and, possibly, 11 and 12 excitons. Molecules containing from five to ten excitons are apparently unstable.
Fiz. Tverd. Tela (St. Petersburg) 40, 929–931 (May 1998) 相似文献
12.
We examine the absorption and amplification bands of a weak probe signal in the presence of Bose-Einstein condensation of
excitons that emerges in nonequilibrium conditions in the field of coherent laser radiation with a wave vector k
0. We assume that the detuning
from resonance between the energy ħω
ex
(k
0)+L
0 of the exciton level, which is shifted because of exciton-exciton interaction, and the laser photon energy ħω
L
, is generally nonzero. The elementary excitation spectrum consisting of the quasiexcitonic and quasienergy branches determines
the optical properties of the system. When there is real induced Bose-Einstein condensation, at
the two branches touch, as they do in spontaneous Bose-Einstein condensation. In virtual induced Bose-Einstein condensation,
when
, instabilities emerge in the spectrum in certain regions of the k-space. These instabilities are caused by a real transformation of two laser photons into two extracondensate particles. Nonequilibrium
extracondensate excitons strongly affect the absorption and amplification of the probe light signal. We show that light absorption
is due to the quantum transition from the ground state of the crystal to the quasiexcitonic branch of the spectrum. On the
other hand, amplification of the signal is caused by the transition from the quasienergy branch to the ground state of the
crystal. The same transition can be explained by a real transformation of two laser photons into a vacuum photon of frequency
ħcq and a crystal exciton with a wave vector 2k
0−q. Finally, we show that the excitonic absorption and light-amplification bands are essentially anisotropic at
and depend on the orientation of the vectors q and k
0.
Zh. éksp. Teor. Fiz. 112, 167–179 (July 1997) 相似文献
13.
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
14.
A system of interacting, spatially separated excitons and electrons is examined in the presence of a Bose condensate of excitons.
The kinetic properties of the system that are governed by the interaction of excitations in the exciton subsystem with electrons
are investigated. It is shown that a nonequilibrium distribution of excitations in the exciton subsystem gives rise to an
induced electron current. Experimental observation of the kinetic phenomena described can provide new information on the exciton
phase state.
Zh. éksp. Teor. Fiz. 116, 1440–1449 (October 1999) 相似文献
15.
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
16.
The change in the properties of excitonic states near anticrossing is investigated experimentally. It is shown that the phase
relaxation time of light excitons in a GaAs/AlGaAs symmetric double quantum well increases by a factor of five as a result
of mixing of the energy states of light and heavy excitons.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 426–430 (25 March 1999) 相似文献
17.
S. K. Srivastava 《Pramana》2003,60(1):29-45
Lagrangian density of riccions is obtained with the quartic self-interacting potential using higher-derivative gravitational
action in (4 +D)-dimensional space-time withS
D as a compact manifold. It is found that the resulting four-dimensional theory for riccions is one-loop multiplicatively renormalizable.
Renormalization group equations are solved and its solutions yield many interesting results such as (i) dependence of extra
dimensions on the enegy mass scale showing that these dimensions increase with the increasing mass scale up toD = 6, (ii) phase transition at 3.05 × 1016 GeV and (iii) dependence of gravitational and other coupling constants on energy scale. Results also suggest that space-time
above 3.05 × 1016 GeV should be fractal. Moreover, dimension of the compact manifold decreases with the decreasing energy mass scale such thatD = 1 at the scale of the phase transition. Results imply invisiblity of S1 at this scale (which is 3.05 × 1016 GeV). 相似文献
18.
We study a new class of nonlinear cooperative phenomena that occur when light propagates in direct-gap semiconductors. The
nonlinearity here is due to a process, first discussed by A. L. Ivanov, L. V. Keldysh, and V. V. Panashchenko, in which two
excitons are bound into a biexciton by virtue of their Coulomb interaction. For the geometry of a ring cavity, we derive a
system of nonlinear differential equations describing the dynamical evolution of coherent excitons, photons, and biexcitons.
For the time-independent case we arrive at the equation of state of optical bistability theory, and this equation is found
to differ considerably from the equations of state in the two-level atom model and in the exciton region of the spectrum.
We examine the stability of the steady states and determine the switchover times between the optical bistability branches.
We also show that in the unstable sections of the equation of state, nonlinear periodic and chaotic self-pulsations may arise,
with limit cycles and strange attractors being created in the phase space of the system. The scenario for the transition to
the dynamical chaos mode is found. A computer experiment is used to study the dynamic optical bistability. Finally, we discuss
the possibility of detecting these phenomena in experiments.
Zh. éksp. Teor. Fiz. 112, 1778–1790 (November 1997) 相似文献
19.
We study the process of magnetic ordering in planar antiferromagnetic systems with a Kagomé lattice. It is found that if the
interaction between next-nearest-neighbor spins is taken into account, the heat capacity of such systems has a singularity
at a finite temperature T. On the basis of a scaling analysis of finite-size systems we study the behavior of thermodynamic quantities in the neighborhood
of a phase transition. We find that the phase transition at the critical point is due to discrete-and continuous-symmetry
breaking, in which the long-range chiral order and the power-law translational spin order emerge simultaneously. Finally,
we calculate the temperatures of the transition to different (with three and nine spins per unit cell) ordered states.
Zh. éksp. Teor. Fiz. 113, 2209–2220 (June 1998) 相似文献
20.
J. Collet 《Journal of Physics and Chemistry of Solids》1985,46(4):417-422
In this work, we study the stability of excitons at high density, i.e. we calculate the reduction of the exciton binding energy due to exciton-exciton interactions in a high-density exciton gas. We derive first the effective electron-hole interaction in the presence of free carriers and excitons. We use the static approximation. The exciton binding energy is calculated by the variational technique. The computations are specialized to GaAs. We investigate the critical density when the exciton binding disappears, which corresponds to the exciton plasma transition. We conclude that this transition occurs at higher density than the reverse plasma exciton transition, determined by the standard criteria a0qD =1.19 [Rogers F. J., Graboske H. C., Jr. and Harword D. J., Phys. Rev.A1, 1577 (1970)]. 相似文献