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1.
It is predicted that an excitonic liquid is formed in a system of spatially separated electrons (e) and holes (h) in a system of two coupled quantum wells. The ground-state energy and the equilibrium density of the excitonic liquid are
calculated as a function of the distance D between the wells. A gas-liquid quantum transition with increasing D is studied. The Berezinskii-Kosterlitz-Thouless transition temperatures at which superfluidity appears in the system are
found (for different D). A quantum Mott metal-insulator transition in an anisotropic double-quantum-well structure is investigated. The region of
existence of crystalline order in a system of spatially separated e and h is studied. Possible experimental manifestations of the predicted effects are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 526–531 (25 October 1996) 相似文献
2.
V. S. Bagaev V. S. Krivobok S. N. Nikolaev E. E. Onishchenko A. A. Pruchkina D. F. Aminev M. L. Skorikov D. N. Lobanov A. V. Novikov 《Journal of Experimental and Theoretical Physics》2013,117(5):912-925
The dynamics of the phase transition from an electron-hole plasma to an exciton gas is studied during pulsed excitation of heterostructures with Si1 ? x Ge x /Si quantum wells. The scenario of the phase transition is shown to depend radically on the germanium content in the Si1 ? x Ge x layer. The electron-hole system decomposes into a rarefied exciton and a dense plasma phases for quantum wells with a germanium content x = 3.5% in the time range 100–500 ns after an excitation pulse. In this case, the electron-hole plasma existing in quantum wells has all signs of an electron-hole liquid. A qualitatively different picture of the phase transition is observed for quantum wells with x = 9.5%, where no separation into phases with different electronic spectra is detected. The carrier recombination in the electron-hole plasma leads a gradual weakening of screening and the appearance of exciton states. For a germanium content of 5–7%, the scenario of the phase transition is complex: 20–250 ns after an excitation pulse, the properties of the electron-hole system are described in terms of a homogeneous electron-hole plasma, whereas its separation into an electron-hole liquid and an exciton gas is detected after 350 ns. It is shown that, for the electron-hole liquid to exist in quantum wells with x = 5–7% Ge, the exciton gas should have a substantially higher density than in quantum wells with x = 3.5% Ge. This finding agrees with a decrease in the depth of the local minimum of the electron-hole plasma energy with increasing germanium concentration in the SiGe layer. An increase in the density of the exciton gas coexisting with the electron-hole liquid is shown to enhance the role of multiparticle states, which are likely to be represented by trions T + and biexcitons, in the exciton gas. 相似文献
3.
A Mott exciton in coupled quantum wells in a transverse magnetic field H is considered. An expression for the exciton spectrum in an arbitrary magnetic field for large separations D between quantum wells containing an electron (e) and a hole (h) is given. The exciton spectrum in a strong magnetic field for different Landau levels at arbitrary D has been calculated. Changes in the parameter D/l, where
is the magnetic length, cause rearrangement of the magnetoexciton dispersion curves ℰ(P), where P is the conserved “magnetic” momentum, which is a function of the separation between the electron and hole in the plane of
the quantum wells. Off-center (“roton”) extrema occur only for D/l,<(D/l)cr, where (D/l)cr is a function of the exciton quantum numbers n and m. The magnetoexciton effective mass in states with magnetic quantum number m=0 monotonically increases with H and D, while in states with m≠0 it is a nonmonotonic function of D/l. The probability of generating an exciton in coupled quantum wells increases with H. Absorption of electromagnetic radiation due to transitions between excitonic levels in coupled quantum wells is discussed.
For an exciton containing a heavy hole the oscillator strengths
increase with H and the oscillator strengths
decrease.
Zh. éksp. Teor. Fiz. 112, 1791–1808 (November 1997) 相似文献
4.
This paper discusses a quantum-mechanical metal-insulator transition that occurs in an anisotropic electron-hole system with
the electrons and holes separated and confined to a double quantum well. The critical concentration n
c of carriers in the system above which the excitonic (insulating) phase becomes an electron-hole (metallic) phase is investigated,
along with its dependence on the distance between wells D.
Fiz. Tverd. Tela (St. Petersburg) 39, 1654–1656 (September 1997) 相似文献
5.
A. V. Platonov V. P. Kochereshko D. R. Yakovlev W. Ossau A. Waag G. Landwehr F. Bassani R. T. Cox 《JETP Letters》1997,65(1):45-52
A method has been developed for recording and analyzing the differential magnetoreflection (magnetotransmission) spectra of
semiconductor structures with quantum wells. The method was used to determine the exciton g-factor in semimagnetic CdTe/(Cd, Mn)Te heterostructures with quantum wells. In nonmagnetic structures with quantum wells
containing a two-dimensional electron gas, the excitonic damping depends on the spin state of the exciton. This effect is
explained by the exchange contribution to exciton-electron scattering.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 44–49 (10 January 1997) 相似文献
6.
R. Mélin D. Feinberg 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):101-114
We derive a microscopic transport theory of multiterminal hybrid structures in which a superconductor is connected to several
spin-polarized electrodes. We discuss the non-perturbative physics of extended contacts, and show that such contacts can be
well represented by averaging out the phase of the electronic wave function. The intercontact Andreev reflection and elastic
cotunneling conductances are identical if the phase can be averaged out, namely in the presence of at least one extended contact.
The maximal conductance of a two-channel contact is proportional to (e
2/h)(a
0/D)2exp[-D/ξ(ω*)], where D is the distance between the contacts, a0 the lattice spacing, ξ(ω) is the superconducting coherence length, and ω* is the cross-over frequency between a perturbative regime ( ω < ω*) and a non perturbative regime ( ω* < ω < Δ).
Received 18 June 2001 and Received in final form 17 January 2002 相似文献
7.
The temperature T
c
of the Kosterlitz-Thouless transition to a superfluid state for a system of magnetoexcitons with spatially separated electrons
e and holes h in coupled quantum wells is obtained as a function of magnetic field H and interlayer separation D. It is found that T
c
decreases as a function of H and D at fixed exciton density n
ex
as a result of an increase in the exciton magnetic mass. The highest Kosterlitz-Thouless transition temperature as a function
of H increases (at small D) on account of an increase in the maximum magnetoexciton density n
ex
versus magnetic field, where n
ex
is determined by a competition between the magnetoexciton energy and the sum of the activation energies of incompressible
Laughlin fluids of electrons and holes.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 5, 332–337 (10 September 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
8.
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
9.
An analysis is made of the region of existence of crystalline order in a system of spatially separated electrons (e) and holes (h) in two coupled quantum wells for various concentrations n, temperatures T, and distances D between the layers. A study is also made of crystallization in a system of electrons in semiconductor structures near a metal
electrode for various distances d between the semiconductor and the metal. Calculations of the crystalline phase were made using variational calculations of
the ground-state energy of the system allowing for pairing of quasiparticles with nonzero momentum. For a system of two coupled
quantum wells, regions in (T,n,D) space are determined in which electron (or hole) charge-density waves exist in each layer and regions where these charge-density
waves are in phase, in other words, indirect excitons (or pairs with spatially separated electrons and holes) interacting
as electric dipoles, become crystallized. In the electron system in semiconductor structures near a metal electrode, regions
of existence of an electron crystal are also obtained in (T,n,D) space, where over large distances the electrons interact as electric dipoles because of image forces.
Fiz. Tverd. Tela (St. Petersburg) 40, 1350–1355 (July 1998) 相似文献
10.
The paper considers the effect of a magnetic field B on the transport of neutral composite particles, namely excitons, in weakly disordered two-dimensional (2D) systems. In the
case of classical transport (when the interference of different paths is neglected), the magnetic field suppresses exciton
transport, and the static diffusion constant D(B) monotonically drops with B. When quantum-mechanical corrections due to weak localization are taken into account, D(B) becomes a nonmonotonic function of B. In weak magnetic fields, where the magnetic length is much larger than the exciton Bohr radius, ℓB=(ℏc/eB)1/2≫a
B
=ε ℏ2/μe
2,a positive magnetodiffusion effect is predicted, i.e., the exciton mobility should increase with B.
Zh. éksp. Teor. Fiz. 114, 359–378 (July 1998) 相似文献
11.
The evolution of indirect exciton luminescence in AlAs/GaAs coupled quantum wells after excitation by pulsed laser radiation
has been studied in strong magnetic fields (B⩽12 T) at low temperatures (T⩾1.3 K), both in the normal regime and under conditions of anomalously fast exciton transport, which is an indication of the
onset of exciton superfluidity. The energy relaxation rate of indirect excitons measured in the range of relaxation times
between several and several hundreds of nanoseconds is found to be controlled by the properties of the exciton transport,
specifically, this parameter increases with the coefficient of excitonic diffusion. This behavior is qualitatively explained
in terms of migration of excitons between local minima of the random potential in the plane of the quantum well.
Zh. éksp. Teor. Fiz. 114, 1115–1120 (September 1998) 相似文献
12.
J.J. Liu S.F. Zhang Y.X. Li X.J. Kong 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):17-20
Using a two-parameter wave function, we calculate variationally the binding energy of an exciton bound to an ionized donor
impurity (D+,X) in GaAs-AlxGa1-xAs quantum wells for the values of the well width from 10 to 300 ?, when the dopant is located in the center of the well and
at the edge of the well. The theoretical results confirm that the previous experimental speculation proposed by Reynolds et al. [Phys. Rev. B 40, 6210 (1989)] is the binding energy of D+,X for the dopant at the edge of the well. In addition, we also calculate the center-of-mass wave function of the exciton and
the average interparticle distances. The results are discussed in detail.
Received 17 July 2000 and Received in final form 13 November 2000 相似文献
13.
E. L. Ivchenko V. P. Kochereshko A. V. Platonov D. R. Yakovlev A. Waag W. Ossau G. Landwehr 《Physics of the Solid State》1997,39(11):1852-1858
Theory of specular light reflection from long-period quantum-well structures taking into account the exciton contribution
to dielectric polarization has been developed for an arbitrary relation between the background refractive index in the well,
n
a, and barrier-material refractive index nb. General expressions for the optical reflection and transmission coefficients for a structure with N equidistant quantum wells are derived with the use of the Green’s function and transfer matrix methods. Normal and oblique
light reflectance spectra from II-VI-based heterostructures were found to reveal a bright interference pattern caused by the
difference between n
a and n
b. A comparison of the theory with experiment has yielded the dispersion of n
a and n
b within a broad wavelength range and the parameters of the quasi-two-dimensional heavyhole exciton (e1-hh1), namely, the resonant frequency and the radiative and nonradiative damping rates. Reflectance spectra from resonant Bragg
and quasi-Bragg structures with real exciton parameters are calculated, and the effect on these spectra of the refractive-index
difference and the deviation from the Bragg condition is analyzed.
Fiz. Tverd. Tela (St. Petersburg) 39, 2072–2078 (November 1997) 相似文献
14.
X-ray diffraction is used to study the temperature dependence of the lattice parameters and the sequence of structural realignments
in crystalline Rb2ZnCl4 over temperatures of 4.2–310 K. The appearance of and changes in the system of satellite reflexes indicative of structural
ordering are studied. Below 74 K, on going into the monoclinic phase (space group A11a), anomalies are observed in the behavior of the lattice parameters, and superstructural reflexes develop with wave vectors
q=a
*/3+b
*/2+c
*/2 corresponding to an increase by a large factor in initial parameters a, b, and c of the Pnma-phase.
Fiz. Tverd. Tela (St. Petersburg) 41, 1084–1090 (June 1999) 相似文献
15.
The indirect Mott exciton (spatially-separated electron and hole) in coupled quantum wells in crossed electric and magnetic
fields is discussed. The exciton spectrum is calculated for the case where the distance between the quantum wells of the electron
and hole is larger than the exciton Bohr radius. The magnetoexciton creation probability is calculated and its dependence
on the electric field is found. The absorption of electromagnetic radiation between the indirect magnetoexciton levels in
coupled quantum wells is discussed.
Fiz. Tverd. Tela (St. Petersburg) 39, 2220–2223 (December 1997) 相似文献
16.
The problem of exciton light absorption in quasi-two-dimensional inhomogeneous systems in a strong transverse magnetic field
H is analyzed. We assume that a random Gaussian field (“white noise”) acting separately on an electron and a hole is due to
(1) fluctuations in the quantum well thickness or (2) fluctuations in the concentrations of the solid solution components.
The problem of a magnetoexciton in a random Gaussian white noise field has been reduced to the problem of the motion in an
H-dependent effective field of a single particle with the effective magnetic mass of the exciton, which is a function of the
magnetic field and parameters of the quantum wells, in a field characterized by “colored noise,” whose correlation function
is different from that of the white noise field. In this approximation, the problem of a magnetoexciton in isolated and coupled
quantum dots is considered. In the coherent-potential approximation, the exciton absorption in random fields of the first
and second type in single and coupled quantum wells has been calculated. The absorption decreases as H increases in the range of strong magnetic fields, which is in agreement with experimental data.
Zh. éksp. Teor. Fiz. 114, 1451–1465 (October 1998) 相似文献
17.
18.
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
19.
《The European Physical Journal C - Particles and Fields》2007,51(2):301-315
Diffractive photoproduction of D*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb-1. The D* mesons were reconstructed in the kinematic range: transverse momentum pT(D*) > 1.9 GeV and pseudorapidity |η(D*)|<1.6, using the decay D*+→D0π+
s followed by D0→K-π+(+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing
proton. Cross sections are reported for photon–proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon
virtualities Q2 < 1 GeV2, in two ranges of the Pomeron fractional momentum xIP<0.035 and xIP<0.01. The relative contribution of diffractive events to the inclusive D*±(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various
parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation. 相似文献
20.
The possibility of magnetic field control of the spectral and polarization characteristics of exciton recombination is examined
in Cd(Mg, Mn) Te-based asymmetric double quantum wells. At low fields, the exciton transition in a semimagnetic well is higher
in energy than that in a nonmagnetic well and the interwell exciton relaxation is fast. In contrast, when the energy order
of the exciton transitions reverses at high fields, unexpectedly slow relaxation of σ− polarized excitons from the nonmagnetic well to the σ+-polarized ground state in the semimagnetic well is observed. Strong dependence of the total circular polarization degree
on the heavy-light hole splitting Δ
hh-lh
in the nonmagnetic well is found and attributed to the spin dependent interwell tunneling controlled by exciton spin relaxation.
Such a slowing down of the relaxation allows separation of oppositely spin-polarized excitons in adjacent wells.
The text was submitted by the authors in English. 相似文献