15 research outputs found
Non-perturbation theory of electronic dynamic conductivity for two-barrier resonance tunnel nano-structure
The non-perturbation theory of electronic dynamic conductivity for open
two-barrier resonance tunnel structure is established for the first time within
the model of rectangular potentials and different effective masses of electrons
in the elements of nano-structure and the wave function linear over the
intensity of electromagnetic field. It is proven that the results of the theory
of dynamic conductivity, developed earlier in weak signal approximation within
the perturbation method, qualitatively and quantitatively correlate with the
obtained results. The advantage of non-perturbation theory is that it can be
extended to the case of electronic currents interacting with strong
electromagnetic fields in open multi-shell resonance tunnel nano-structures, as
active elements of quantum cascade lasers and detectors.Comment: 10 pages, 2 figure
Quasi-stationary states of electrons interacting with strong electromagnetic field in two-barrier resonance tunnel nano-structure
An exact solution of non-stationary Schrodinger equation is obtained for a
one-dimensional movement of electrons in an electromagnetic field with
arbitrary intensity and frequency. Using it, the permeability coefficient is
calculated for a two-barrier resonance tunnel nano-structure placed into a
high-frequency electromagnetic field. It is shown that a nano-structure
contains quasi-stationary states the spectrum of which consists of the main and
satellite energies. The properties of resonance and non-resonance channels of
permeability are displayed.Comment: 8 pages, 3 figure
Energy spectrum of localized quasiparticles renormalized by multi-phonon processes at finite temperature
The theory of renormalized energy spectrum of localized quasi-particle
interacting with polarization phonons at finite temperature is developed within
the Feynman-Pines diagram technique. The created computer program effectively
takes into account multi-phonon processes, exactly defining all diagrams of
mass operator together with their analytical expressions in arbitrary order
over the coupling constant. Now it is possible to separate the pole and
non-pole mass operator terms and perform a partial summing of their main terms.
The renormalized spectrum of the system is obtained within the solution of
dispersion equation in the vicinity of the main state where the high- and
low-energy complexes of bound states are observed. The properties of the
spectrum are analyzed depending on the coupling constant and the temperature.Comment: 16 pages, 3 figures, 3 table
Dynamic conductivity of symmetric three-barrier plane nanosystem in constant electric field
The theory of dynamic conductivity of nanosystem is developed within the
model of rectangular potentials and different effective masses of electron in
open three-barrier resonance-tunnel structure in a constant homogeneous
electric field. The application of this theory for the improvement of operating
characteristics of quantum cascade laser active region (for the experimentally
investigated InGaAs/InAlAs heterosystem)
proves that for a certain geometric design of nanosystem there exists such
minimal magnitude of constant electric field intensity, at which the
electromagnetic field radiation power together with the density of current
flowing through the separate cascade of quantum laser becomes maximal.Comment: 7 pages, 2 figure
Renormalized energy of ground and first excited state of Fr\"{o}hlich polaron in the range of weak coupling
Partial summing of infinite range of diagrams for the two-phonon mass
operator of polaron described by Fr\"{o}hlich Hamiltonian is performed using
the Feynman-Pines diagram technique. Renormalized spectral parameters of ground
and first excited (phonon repeat) polaron state are accurately calculated for a
weak electron-phonon coupling at K. It is shown that the stronger
electron-phonon interaction shifts the energy of both states into low-energy
region of the spectra. The ground state stays stationary and the excited one
decays at a bigger coupling constant.Comment: 12 pages, 5 figure
Optimization of quantum cascade laser operation by geometric design of cascade active band in open and closed models
Using the effective mass and rectangular potential approximations, the theory
of electron dynamic conductivity is developed for the plane multilayer
resonance tunnel structure placed into a constant electric field within the
model of open nanosystem, and oscillator forces of quantum transitions within
the model of closed nanosystem. For the experimentally produced quantum cascade
laser with four-barrier active band of separate cascade, it is proven that just
the theory of dynamic conductivity in the model of open cascade most adequately
describes the radiation of high frequency electromagnetic field while the
electrons transport through the resonance tunnel structure driven by a constant
electric field.Comment: 10 pages, 2 figure
Generalized method of Feynman-Pines diagram technique in the theory of energy spectrum of two-level quasiparticle renormalized due to multi-phonon processes at cryogenic temperature
Theory of the spectrum of localized two-level quasi-particle renormalized due
to interaction with polarization phonons at cryogenic temperature is developed
using the generalized method of Feynman-Pines diagram technique. Using the
procedure of partial summing of infinite ranges of the main diagrams, mass
operator is obtained as a compact branched chain fraction, which effectively
takes into account multi-phonon processes. It is shown that multi-phonon
processes and interlevel interaction of quasiparticle and phonons cardinally
change the renormalized spectrum of the system depending on the difference of
energies of two states, which either resonates with phonon energy or does not.
The spectrum of non-resonant system contains renormalized energies of the main
states and two similar infinite series of groups of phonon satellite levels.
The spectrum of a resonant system contains a renormalized ground state and
infinite series of satellite groups.Comment: 14 pages, 2 figures, 1 tabl
Теорія динамічної провідності трибар’єрної резонансно-тунельної структури з двофотонними лазерними переходами
Within the approximation of effective mass and rectangular potential barriers for the electron and using the obtained solutions of complete Schrodinger equation, the theory of dynamic conductivity for three-barrier resonant tunneling structure (InGaAs/InAlAs) with different depths of potential wells driven by weak electromagnetic field is developed in one- and two-photon approach.
It is shown that varying Ga concentration one can obtain such geometric configurations of nanostructure, being an active region of quantum cascade laser, in which the increasing intensity of laser radiation, produced by electron quantum transitions accompanied by radiation of two photons with equal energy, is observed. It is established that the contribution of two-photon transitions into the complete magnitude of dynamic conductivity is not smaller than 37 %.У наближенні ефективних мас та прямокутних потенціальних ям і бар’єрів для електрона, з використанням знайдених розв’язків повного рівняння Шредінгера, розвинена теорія активної динамічної провідності трибар’єрної резонансно-тунельної структури (InGaAs/InAlAs) з різними глибинами потенціальних ям у слабкому електромагнітному полі в одно- та двофотонному наближенні.
Показано, що зміною концентрації Ga можна отримати такі геометричні конфігурації наноструктури, як активної зони квантового каскадного лазера, в яких на основі електронних квантових переходів з випромінюванням двох фотонів однакової енергії відбувається зростання інтенсивності лазерного випромінювання. Встановлено, що вклад двофотонних переходів у сумарну величину динамічної провідності складає не менше ніж 37 %
Electron and Exciton Quasi-Stationary s-States in Open Spherical Quantum Dots
The theoretical calculation of spectral parameters of electron and exciton quasi-stationary s-states in open spherical quantum dot is performed within the effective mass approximation and rectangular potentials model. The conceptions of probability distribution functions (over quasi-momentum or energy) of electron location inside of quantum dot and their spectral characteristics: generalized resonance energies and widths are introduced. It is shown that the generalized resonance energies and widths, obtained within the distribution functions, satisfy the Heisenberg uncertainty principle for the barrier widths varying from zero to infinity. At the same time, the ordinary resonance energies and widths defined as complex poles of scattering S-matrix, do not satisfy it for the small barrier widths and, therefore, are correct only for the open quantum dots with rather wide potential barriers