共查询到20条相似文献,搜索用时 15 毫秒
1.
E. V. Ponizovskaya A. M. Bratkovsky 《Applied Physics A: Materials Science & Processing》2009,95(4):1137-1142
Negative index materials (NIM) enable subwavelength resolution and are promising for applications in integrated optical systems,
since the mode volume is small. Most promising NIM systems essentially use noble metals (Ag, Au) with material losses much
lower than in other metals, but still rather hefty, like in metal–dielectric–metal “fishnets”. Therefore, we perform extensive
finite-difference time-domain modeling of NIM “fishnets” in combination with gain medium, InGaAsP multiple quantum wells in
the present work. The signal recovery is weak, which is related to weak overlap between the radiation field and the gain medium.
The signal modulation speed may be very large, in a picosecond range. 相似文献
2.
F. Crisciani R. Purini 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):571-575
The present note deals with Munk's ocean model and proposes an alternative approach to find its solution, with special regard
to the western boundary layer. We introduce a suitable “distance” between the related Sverdrup streamfunction and all the
admissible streamfunctions which are valid in the western boundary layer. We prove that such distance has a minimum that singles
out a unique solution. Unlike the traditional method, this procedure works without assuming a priori any dynamic boundary
condition.
Received 16 July 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: fulcri@itt.ts.cnr.it 相似文献
3.
Z. P. Wang X. X. Liang X. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):41-46
Polaron effects on excitons in parabolic quantum wells are
studied theoretically by using a variational approach with the so-called
fractional dimension model. The numerical results for the exciton binding
energies and longitudinal-optical phonon contributions in
GaAs/Al0.3Ga0.7As parabolic quantum well structures are obtained as functions of the well width. It is shown that the exciton binding energies
are obviously reduced by the electron (hole)-phonon interaction and the polaron effects are un-negligible. The results demonstrate
that the fractional-dimension variational theory is effectual in the investigations of excitonic polaron problems in parabolic
quantum wells. 相似文献
4.
Properties of excitons in vertically coupled GaAs/AlGaAs quantum dots were investigated using the variational method within the envelope function and effective mass approximations. It was found that when the thickness of the spacer layer becomes less than about one exciton Bohr radius, both the exciton binding energy and the fundamental optical transition energy are reduced compared to those in isolated quantum dots. This is a result of increased space extension of exciton due to the penetration of carrier wave functions into the spacer layer and corresponding reduction in confinement energy which dominates over the Coulomb interaction between the electron and the hole. 相似文献
5.
M. Combescot M.-A. Dupertuis 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(3):459-464
We show that the carrier “antibinding” observed recently in
semiconductor quantum dots, i.e., the fact that the ground state
energy of two electron-hole pairs goes above twice the ground-state
energy of one pair, can entirely be assigned to a charge separation
effect, whatever its origin. In the absence of external electric field, this charge
separation comes from different “spreading-out” of the electron and
hole wavefunctions linked to the finite height of the barriers. When
the dot size shrinks, the two-pair energy always stays below when the
barriers are infinite. On the opposite, because barriers are less
efficient for small dots, the energy of two-pairs in a dot with
finite barriers, ends by behaving like the one in bulk, i.e., by
going above twice the one-pair energy when the pairs get too close.
For a full understanding of this “antibinding” effect, we have also
reconsidered the case of one pair plus one carrier. We find that,
while the carriers just have to spread out of the dot differently for
the “antibinding” of two-pairs to appear, this “antibinding” for
one pair plus one carrier only appears if this carrier is the one
which spreads out the less. In addition a remarkable sum rule exists
between the “binding energies” of two pairs and of one pair plus one carrier. 相似文献
6.
D. K. Loginov E. V. Ubyĭvovk Yu. P. Efimov V. V. Petrov S. A. Eliseev Yu. K. Dolgikh I. V. Ignat’ev V. P. Kochereshko A. V. Sel’kin 《Physics of the Solid State》2006,48(11):2100-2108
The optical reflection spectra of semiconductor GaAs/AlGaAs structures with wide quantum wells are studied experimentally. A theoretical analysis of the spectra is performed in terms of the exciton-polariton model in the approximation of quantum confinement of the exciton center of mass with regard to the contributions of both heavy and light excitons to the crystal polarization. The applicability range of the theory of the center-of-mass confinement for GaAs/AlGaAs heterostructures is estimated. It is established that, for quantum wells more than 180 nm wide, the interference effects observed in the reflection spectra of polariton waves are reproduced, to a good accuracy, by theoretical calculations based on the quantum confinement of the exciton center of mass. For quantum-well widths less than 150 nm, the experimental results are described better by the model of quantum confinement of electrons and holes. 相似文献
7.
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
8.
J. B. Xia X. W. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):415-420
The electronic structure and optical properties of ZnO wurtzite
quantum wires with radius R≥3 nm are studied in the framework
of six-band effective-mass envelope function theory. The hole
effective-mass parameters of ZnO wurtzite material are calculated
by the empirical pseudopotential method. It is found that the
electron states are either two-fold or four-fold degenerate. There
is a dark exciton effect when the radius R of the ZnO quantum
wires is in the range of [3,19.1] nm (dark range in our model).
The dark ranges of other wurtzite semiconductor quantum wires are
calculated for comparison. The dark range becomes smaller when the
|Δso| is larger, which also happens in the quantum-dot
systems. The linear polarization factor of ZnO quantum wires is
larger when the temperature is higher. 相似文献
9.
Ci-bo LOU Li-qin TANG Dao-hong SONG Xiao-sheng WANG Jing-jun XU Zhi-gang CHEN 《Frontiers of Physics in China》2008,3(1):1-12
The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics,
and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced
waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart
in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent
coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array,
a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in
the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in
a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such
photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential
applications in optical switching and navigation. In this review article, we present a brief overview on our experimental
demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping
of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study
of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein
condensates) propagating in periodic potentials.
相似文献
10.
J. Gomis J. Martínez-Pastor B. Alén D. Granados J. M. García P. Roussignol 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):471-477
We present a study of the primary optical transitions
and recombination dynamics in InGaAs self-assembled quantum
nanostructures with different shape. Starting from the same
quantum dot seeding layer, and depending on the overgrowth
conditions, these new nanostructures can be tailored in shape and
are characterized by heights lower than 2 nm and base lengths
around 100 nm. The geometrical shape strongly influences the
electronic and optical properties of these nanostructuctures. We
measure for them ground state optical transitions in the range
1.25–1.35 eV and varying energy splitting between their excited
states. The temperature dependence of the exciton recombination
dynamics is reported focusing on the intermediate temperature
regime (before thermal escape begins to be important). In this
range, an important increase of the effective photoluminescence
decay time is observed and attributed to the state filling and
exciton thermalization between excited and ground states. A rate
equation model is also developed reproducing quite well the
observed exciton dynamics. 相似文献
11.
P. Sujanah 《Phase Transitions》2017,90(3):213-226
Pressure-induced binding energies of an exciton and a biexciton are studied taking into account the geometrical confinement effect in a CdTe/ZnTe quantum dot. Coulomb interaction energy is obtained using Hartree potential. The energy eigenvalue and wave functions of exciton and the biexciton are obtained using the self-consistent technique. The effective mass approximation and BenDaniel-Duke boundary conditions are used in the self-consistent calculations. The pressure-induced nonlinear optical absorption coefficients for the heavy hole exciton and the biexciton as a function of incident photon energy for CdTe/ZnTe quantum dot are investigated. The optical gain coefficient with the injection current density, in the presence of various hydrostatic pressure values, is studied in a CdTe/ZnTe spherical quantum dot. The pressure-induced threshold optical pump intensity with the dot radius is investigated. The results show that the pressure-induced electronic and optical properties strongly depend on the spatial confinement effect. 相似文献
12.
CdTe nanocrystals were grown from commercially available RG850 Schott filter glass by two-step heat-treatment process which almost doubles the particle to matrix volume fraction. A calculation shows that a quantized-state effective mass model in the strong confinement regime might be used to deduce the average radius for the nanocrystals larger than 2 nm in radius from the energetic position of the first exciton peak in optical absorption spectrum. Size-induced shift of ∼360 meV in the first exciton peak position was observed. The steady state photoluminescence spectra exhibit a broad band red shifted relative to the first exciton band, which indicates the existence of shallow trap states. The non-linear optical properties of CdTe nanocrystals were studied by room temperature resonant photoabsorption spectroscopy. The differential absorption spectra had three-lobed structure whose size-dependent evolution was explained by bleaching of the absorption, red shift and broadening in the Gaussian absorption band used to fit the first exciton peak. A maximum red shift of 2.32 meV for the average nanocrystal radius of 4.65 nm was estimated by fitting the photomodulation spectra with a combination of first and second derivative Gaussian absorption bands. We presume that the red shift is induced by the electric field of trapped charges in surface states. Internal electric field strengths of 23 and 65 kV/cm were predicted for the average nanocrystal radii of 3.95 and 4.65 nm, respectively, with the help of second-order perturbation theory in the strong confinement limit. 相似文献
13.
The electric field created by a point dipole located in a dielectric void (“bubble”) is calculated. We consider a continuous
profile of the medium permittivity and find that, at large distances, the effective dipole field depends on the model chosen
for the bubble walls, in particular their thickness. A boundary layer model is analyzed that gives good agreement with numerical
calculations. Our results shed light on the local field correction that has attracted lot of interest lately. 相似文献
14.
R.I. Eglitis E.A. Kotomin G. Borstel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):483-486
The origin of the intrinsic excitonic (“green”) luminescence in ABO3 perovskites remains a hot topic over the last quarter of a century. We suggest as a theoretical interpretation for the “green”
luminescence in these crystals, the recombination of electron and hole polarons forming a charge transfer vibronic exciton.
In order to check quantitatively the proposed model, we performed quantum chemical calculations using the Intermediate Neglect
of Differential Overlap (INDO) method combined with the periodic defect model. The luminescence energies calculated for four
perovskite crystals are found to be in good agreement with experimental data.
Received 19 December 2001 and Received in final form 14 March 2002 Published online 25 June 2002 相似文献
15.
R. Driben B. A. Malomed 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,50(3):317-323
It is known that optical-lattice (OL) potentials can stabilize solitons and
solitary vortices against the critical collapse, generated by cubic
attractive nonlinearity in the 2D geometry. We demonstrate that OLs can also
stabilize various species of fundamental and vortical solitons against the
supercritical collapse, driven by the double-attractive cubic-quintic
nonlinearity (however, solitons remain unstable in the case of the pure
quintic nonlinearity). Two types of OLs are considered, producing similar
results: the 2D Kronig-Penney “checkerboard”, and the sinusoidal potential.
Soliton families are obtained by means of a variational approximation, and
as numerical solutions. The stability of all families, which include
fundamental and multi-humped solitons, vortices of oblique and straight
types, vortices built of quadrupoles, and supervortices, strictly
obeys the Vakhitov-Kolokolov criterion. The model applies to optical media
and BEC in “pancake” traps. 相似文献
16.
本文将基于有效质量近似下的变分法,理论研究了纤锌矿InGaN/GaN staggered量子阱中的激子态和光学性质.数值结果显示了InGaN量子阱中的量子尺寸和staggered受限垒对束缚于量子阱中的激子态和光学性质有着明显的影响.当阱宽增加时,量子受限效应减弱,激子结合能降低,带间发光波长增加.另一方面,当量子阱中staggered受限势增加时,量子受限效应增强,激子结合能升高,带间发光波长降低.本文的理论结果证明了可以通过调节staggered垒高和量子尺寸来调控纤锌矿InGaN staggered量子阱中的激子态和光学性质. 相似文献
17.
I.V. Ponomarev L.I. Deych V.A. Shuvayev A.A. Lisyansky 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):539-553
We introduce a computationally efficient approach to calculating characteristics of excitons in quantum wells. In this approach we derive a system of self-consistent equations describing the motion of an electron–hole pair. The motion in the growth direction of the quantum well in this approach is separated from the in-plane motion, but each of them occurs in modified potentials found self-consistently. The approach is applied to shallow quantum wells, for which we obtained an analytical expression for the exciton binding energy and the ground state eigenfunction. Our numerical results yield lower exciton binding energies in comparison to standard variational calculations, while require reduced computational effort. 相似文献
18.
本文将基于有效质量近似下的变分法,理论研究了纤锌矿InGaN/GaN staggered 量子阱中的激子态和光学性质。数值结果显示了InGaN量子阱中的量子尺寸和staggered受限垒对束缚于量子阱中的激子态和光学性质有着明显地影响。当阱宽增加时,量子受限效应减弱,激子结合能降低, 带间发光波长增加。另一方面,当量子阱中staggered受限势增加时,量子受限效应增强,激子结合能升高,带间发光波长降低。本文的理论结果证明了可以通过调节staggered垒高和量子尺寸来调控纤锌矿InGaN staggered 量子阱中的激子态和光学性质。 相似文献
19.
The present work investigates the excitonic effects on the bilayer graphene with layers of different thickness under the influence of external electric field through a simple numerical approach. The band structure and energy gap have been calculated using a tight-binding model including parameters like the second-nearest-neighbor-hopping energies t′ (in-plane) and γ (intra-layer) and the on-site energy Δ, in details. The binding energy of exciton for bilayer graphene has been calculated by Wannier model and Hartree–Fock approximation through the Bethe–Salpeter equation. Finally the optical conductivity spectrum of bilayer graphene has been calculated by using the effective mass approximation in two band model. 相似文献
20.
We analyze the possibility of applying the Kramers-Kronig relations to media with substantial spatial diffusion of the permittivity,
in which case additional light waves of the Pekar type emerge. The calculations are done within a broad range of values of
the exciton damping constant G with and without a “dead layer” at the crystal surface. We establish the condition in which
the use of the Kramers-Kronig relations in calculating the optical constants of the substance yields correct results.
Zh. éksp. Teor. Fiz. 114, 1393–1406 (October 1998) 相似文献