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Журнал прикладной спектроскопии

ФАЗОВЫЙ СИНХРОНИЗМ С УЧАСТИЕМ БОЗЕ-ЭЙНШТЕЙНОВСКОГО КОНДЕНСАТА ЭКСИТОНОВ

Yu. D. Zavorotnev, В.В. Румянцев, А. Г. Петренко, Томашевская Елена Юрьевна

Published Jan 29, 2021• 0 citations
OpenAlex

Abstract

Methods for detecting Bose-Einstein condensate of light and dark excitons are considered. The features of the result radiation during the decay of condensate excitons are investigated. The recombination of these quasiparticles is studied, taking into account phase synchronism.

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arXiv:cond-mat/9904418•Apr 28, 1999•0 citations

DYNAMICS OF BOSE-EINSTEIN CONDENSATE WITH ACCOUNT OF PAIR CORRELATIONS

Yu. M. Poluéktov, A. M. Arslanaliev

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arXiv:1702.06020•East European Journal of Physics•Jan 1, 2017•0 citations

Bose–Einstein Condensation of Mixed States of Excitons and Photons

S. A. Moskalenko, David W. Snoke

Introduction. Polaritons and Semiconductor Microcavities As we have mentioned previously, BEC of excitons or biexcitons and lasing can be seen as two limits of the same theory. Lasing occurs in the case of strong electron-photon coupling (recombination rate fast compared with interparticle-scattering rate) while excitonic BEC occurs in the case of weak electron-photon coupling (recombination rate slow compared with the interparticle-scattering rate.) A laser can be seen as a Bose condensate in which the long-range phase coherence exists in the photon states [1], while in the exciton condensate the coherence exists in the electronic states. This is one of the reasons for some of the confusing debates in the early history of excitonic Bose condensation – in many systems there is not a sharp distinction between an excitonic condensate and supperradiance, i.e., luminescence with enhanced intensity due to stimulated emission [2-4]. In the previous chapters, we have so far considered a laser light source only as a source of excitons by means of quantum transitions. In Chapter 6, the laser radiation was taken into account as a given external factor. This chapter is dedicated to phenomena related to a strong and noticeable exciton-photon interaction, when the light significantly influences the energy spectrum of the high-density excitons [5-9]. As we will see, this leads to many fascinating effects related to instabilities. A strong exciton-photon interaction implies a strong polariton effect, in which photon and exciton states are mixed (as in Fig. 1.3). When this mixing is strong, it is not obvious how to define the ground state of the system.

Cambridge University Press eBooks•Feb 28, 2000•1 citation

Bose-Einstein Condensation of Excitons

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This note discusses the question as to whether quasi-particles, such as excitons, i.e., nonlocalized excited states of solids, can fulfill necessary conditions for a Bose-Einstein condensation, and whether such condensation can be observed. Although uncertainties of present data on excitons preclude precise numerical predictions, it is concluded that under certain experimentally attainable circumstances excitons fulfill the necessary conditions, i.e., condensation is possible. Ways of detecting the condensation are considered, and a specific experiment is proposed.

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New method for detection of exciton Bose condensation using stimulated two-photon emission

Yu. E. Lozovik, A. V. Pushnov

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.

arXiv:cond-mat/9905347•Journal of Experimental and Theoretical Physics•Apr 1, 1999•8 citations
It is shown that for the system of Bose particles it can be obtained the chain of equations for the quasiaverages of the products of field operators, being similar to the Bogolyubov-Born-Green-Kirkwood-Yvon chain in the theory of classical gases.For the case when it is sufficient to confine ourselves to taking account of the quasiaverages of only one field operator and the products of two field operators, the closed system of dynamic equations for Bose-Einstein condensate at zero temperature is obtained which accounts for the one-particle condensate and pair correlations.A spatially homogeneous state in the absence of the external field is considered and the spectrum of small oscillations of the condensate in this case with account of pair correlations is explored.It is shown that the spectrum of collective excitations has two branches: the sound wave branch and the branch with an energy gap at zero momentum.The first of the branches approaches the Bogolyubov spectrum at low momenta, and the second branch -at large momenta.It is discussed the possibility of existence of the quasiparticle excitations with an energy gap in the superfluid helium in connection with the experiment on the absorption of microwave radiation.KEY WORDS: Bose-Einstein condensate, anomalous and normal averages, pair correlations, sound branch of elementary excitations, elementary excitations with energy gap61108, вул.Академічна, 1, Харків, Україна 2 Харківський національний університет ім.В.Н.Каразіна пл.Свободи, 4, м.Харків, 61022, Україна Показано, що в системі бозе-частинок для квазісередніх від добутків польових операторів може бути отримано ланцюжок рівнянь, аналогічний ланцюжку Боголюбова-Борна-Гріна-Кірквуда-Івона в теорії класичних газів.Для випадку, коли досить обмежитися урахуванням тільки квазісередніх від одного польового оператора і добутків двох операторів, отримано замкнуту систему динамічних рівнянь для бозе-ейнштейнівського конденсату при нульовій температурі, яка враховує одночастинковий конденсат і парні кореляції.Розглянуто просторово-однорідний стан при відсутності зовнішнього поля і досліджений спектр малих коливань конденсату в цьому випадку при урахуванні парних кореляцій.Показано, що спектр колективних збуджень має дві гілки, звукову і гілку з енергетичної щілиною при нульовому імпульсі.Перша з гілок наближається до боголюбовського спектру при малих імпульсах, а друга -при великих.Обговорюється можливість існування квазічастинкових збуджень з енергетичної щілиною у надплинному гелії у зв'язку з експериментом по поглинанню НВЧ випромінювання.КЛЮЧОВІ СЛОВА: бозе-ейнштейнівський конденсат, аномальні і нормальні середні, парні кореляції, звукова гілка елементарних збуджень, елементарні збудження з енергетичною щілиноюпл. Свободы, 4, г.Харьков, 61022, Украина Показано, что в системе бозе-частиц для квазисредних от произведений полевых операторов может быть получена цепочка уравнений, аналогичная цепочке Боголюбова-Борна-Грина-Кирквуда-Ивона в теории классических газов.Для случая, когда достаточно ограничиться учетом только квазисредних от одного полевого оператора и произведений двух операторов, получена замкнутая система динамических уравнений для бозе-эйнштейновского конденсата при нулевой температуре, учитывающая одночастичный конденсат и парные корреляции.Рассмотрено пространственно-однородное состояние в отсутствие внешнего поля и исследован спектр малых колебаний конденсата в этом случае при учете парных корреляций.Показано, что спектр коллективных возбуждений имеет две ветви, звуковую и ветвь с энергетической щелью при нулевом импульсе.Первая из ветвей приближается к боголюбовскому спектру при малых импульсах, а вторая -при больших.Обсуждается возможность существования квазичастичных возбуждений с энергетической щелью в сверхтекучем гелии в связи с экспериментом по поглощению СВЧ излучения.
Introduction. Polaritons and Semiconductor Microcavities As we have mentioned previously, BEC of excitons or biexcitons and lasing can be seen as two limits of the same theory. Lasing occurs in the case of strong electron-photon coupling (recombination rate fast compared with interparticle-scattering rate) while excitonic BEC occurs in the case of weak electron-photon coupling (recombination rate slow compared with the interparticle-scattering rate.) A laser can be seen as a Bose condensate in which the long-range phase coherence exists in the photon states [1], while in the exciton condensate the coherence exists in the electronic states. This is one of the reasons for some of the confusing debates in the early history of excitonic Bose condensation – in many systems there is not a sharp distinction between an excitonic condensate and supperradiance, i.e., luminescence with enhanced intensity due to stimulated emission [2-4]. In the previous chapters, we have so far considered a laser light source only as a source of excitons by means of quantum transitions. In Chapter 6, the laser radiation was taken into account as a given external factor. This chapter is dedicated to phenomena related to a strong and noticeable exciton-photon interaction, when the light significantly influences the energy spectrum of the high-density excitons [5-9]. As we will see, this leads to many fascinating effects related to instabilities. A strong exciton-photon interaction implies a strong polariton effect, in which photon and exciton states are mixed (as in Fig. 1.3). When this mixing is strong, it is not obvious how to define the ground state of the system.
This note discusses the question as to whether quasi-particles, such as excitons, i.e., nonlocalized excited states of solids, can fulfill necessary conditions for a Bose-Einstein condensation, and whether such condensation can be observed. Although uncertainties of present data on excitons preclude precise numerical predictions, it is concluded that under certain experimentally attainable circumstances excitons fulfill the necessary conditions, i.e., condensation is possible. Ways of detecting the condensation are considered, and a specific experiment is proposed.
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.