Presence Of Bose-Einstein Condensate Research Articles

Energy relaxation of quantum dot hot electrons in hybrid quantum dot—Bose–Einstein condensate system

The theory of electron energy relaxation in a hybrid structure consisting of quantum dot interacting with a two dimensional exciton gas in Bose–Einstein condensate (BEC) regime is developed. A new type of the relaxation mechanism in the presence of BEC is introduced and theoretically analyzed. It is shown that, in the first order of electron-exciton interaction, two microscopic processes of energy relaxation appear. The first one is related to the emission of a single Bogoliubov excitation (bogolon) by an electron, whereas the second process is associated with the emission of two bogolons. It is shown that the second type processes dominate in the QD electron energy relaxation.

Spin Hall effect for polaritons in a transition metal dichalcogenide embedded in a microcavity

The spin Hall effect for polaritons (SHEP) in a transition metal dichalcogenides (TMDC) monolayer embedded in a microcavity is predicted. We demonstrate that two counterpropagating laser beams incident on a TMDC monolayer can deflect a superfluid polariton flow due to the generation the effective gauge vector and scalar potentials. The components of polariton conductivity tensor for both non-interacting polaritons without Bose-Einstein condensation (BEC)and for weakly-interacting Bose gas of polaritons in the presence of BEC and superfluidity are obtained. It is shown that the polariton flows in the same valley are splitting: the superfluid components of the \textit{A} and \textit{B} polariton flows propagate in opposite directions along the counterpropagating beams, while the normal components of the flows slightly deflect in opposite directions and propagate almost perpendicularly to the beams. The possible experimental observation of SHEP in a microcavity is proposed.

Kinetic description of Bose-Einstein condensation with test particle simulations

We present a kinetic description of Bose-Einstein condensation for particle systems being out of thermal equilibrium, which may happen for gluons produced in the early stage of ultra-relativistic heavy-ion collisions. The dynamics of bosons towards equilibrium is described by a Boltzmann equation including Bose factors. To solve the Boltzmann equation with the presence of a Bose-Einstein condensate we make further developments of the kinetic transport model BAMPS (Boltzmann Approach of MultiParton Scatterings). In this work we demonstrate the correct numerical implementations by comparing the final numerical results to the expected solutions at thermal equilibrium for systems with and without the presence of Bose-Einstein condensate. In addition, the onset of the condensation in an over-populated gluon system is studied in more details. We find that both expected power-law scalings denoted by the particle and energy cascade are observed in the calculated gluon distribution function at infrared and intermediate momentum regions, respectively. Also, the time evolution of the hard scale exhibits a power-law scaling in a time window, which indicates that the distribution function is approximately self-similar during that time.

Coulomb interaction potential and Bose-Einstein condensate

Based on the results of statistical quantum electrodynamics, it is shown that the Coulomb interaction potential of charged particles has no Fourier components at a zero wave vector. This result provides for the possibility of using the grand canonical ensemble to describe the Coulomb system, with independent descriptions of different varieties of charged particles. Based on this, we established that there could be an energy gap in the single-particle excitation spectrum at low pulses, given the presence of Bose-Einstein condensate in the Coulomb system, which does not contradict the existence of collective excitations, characterized by the phonon-roton spectrum.

Large-Napproximation for one- and two-component dilute Bose gases

We discuss the mean-field theories obtained from the leading order in a large-$N$ approximation for one- and two- component dilute Bose gases. For a one-component Bose gas this approximation has the following properties: the Bose-Einstein condensation (BEC) phase transition is second order but the critical temperature $T_c$ is not shifted from the non-interacting gas value $T_0$. The spectrum of excitations in the BEC phase resembles the Bogoliubov dispersion with the usual coupling constant replaced by the running coupling constant which depends on both temperature and momentum. We then study two-component Bose gases with both inter- and intra- species interactions and focus on the stability of the mixture state above $T_c$. Our mean-field approximation predicts an instability from the mixture state to a phase-separated state when the ratio of the inter-species interaction strength to the intra-species interaction strength (assuming equal strength for both species) exceeds a critical value. At high temperature this is a structural transition and the global translational symmetry is broken. Our work complements previous studies on the instability of the mixture phase in the presence of BEC.

Electronic Pumping of Quasiequilibrium Bose-Einstein-Condensed Magnons

We theoretically investigate spin transfer between a system of quasiequilibrated Bose-Einstein-condensed magnons in an insulator in direct contact with a conductor. While charge transfer is prohibited across the interface, spin transport arises from the exchange coupling between insulator and conductor spins. In a normal insulator phase, spin transport is governed solely by the presence of thermal and spin-diffusive gradients; the presence of Bose-Einstein condensation (BEC), meanwhile, gives rise to a temperature-independent condensate spin current. Depending on the thermodynamic bias of the system, spin may flow in either direction across the interface, engendering the possibility of a dynamical phase transition of magnons. We discuss the experimental feasibility of observing a BEC steady state (fomented by a spin Seebeck effect), which is contrasted to the more familiar spin-transfer-induced classical instabilities.

Bose-Einstein condensation and two fluid behavior inHe4

The basic assumption of this paper is that in the presence of Bose-Einstein condensation (BEC) in liquid $^{4}\mathrm{He}$, the wave functions of occupied many particle states are the superposition of two components; a phase coherent component, proportional to the ground state wave function and a phase incoherent component. It is shown that this assumption satisfies necessary conditions imposed by the presence of BEC and that the wave functions of the ideal Bose gas and wave functions of the Bijl-Feynman type are of this form. It is shown that this single assumption provides simple microscopic explanations of essentially all the exotic properties of helium II; why BEC implies two fluid behavior, how the superfluid and condensate fractions are linked, how Landau theory is linked to the presence of BEC, why the superfluid exhibits flow without viscosity and macroscopic quantum effects while the normal fluid does not, how the anomalous expansion and loss of spatial order, observed in helium II as it is cooled, is linked to BEC, and how the presence of sharp peaks observed in the dynamic structure factor are linked with BEC. The theory provides predictions that are in quantitative agreement with a wide range of presently unexplained experimental data on helium II.

Excitonic light-absorption and amplification bands in the presence of laser radiation

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 k0. We assume that the detuning \(\tilde \Delta \) from resonance between the energy ħω ex (k0)+L0 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 \(\tilde \Delta = 0\) the two branches touch, as they do in spontaneous Bose-Einstein condensation. In virtual induced Bose-Einstein condensation, when \(\tilde \Delta < 0\), 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 2k0−q. Finally, we show that the excitonic absorption and light-amplification bands are essentially anisotropic at \(\tilde \Delta \approx 0\) and depend on the orientation of the vectors q and k0.

On the pairing theory of the bose superfluid

In analogy to the BCS theory of superconductivity, a self-consistent pairing theory of the Bose superfluid is developed along lines closely resembling the original Bose pairing model of Valatin and Butler. A new treatment of the zero-wave-vector terms is given which necessitates an attractive part to the interaction in order that a nontrivial solution for the (k-dependent) coherence parameter can exist. It is emphasized that the superfluid phase is best identified with a nonvanishing coherence parameter rather than with the presence of Bose-Einstein condensation, for, in systems with repulsive interactions, condensation can exist in our model without coherence. However, the coherent (superfluid) phase is shown to possess a macroscopic condensation which vanishes at the same temperature,Tλ, that marks the vanishing of coherence. The superfluid spectrum is manifestly gapless and initially linear. Numerical solutions to the self-consistent integral equations atT=0 have been obtained for various pseudopotentials, some of which yield dispersion curves qualitatively resembling helium. The quasi-particle spectrum, condensed fraction, specific heat and sound velocity have been computed as functions of temperature for the complete range 0→Tλ for an attractive Gaussian pseudopotential whilst for more realistic pseudopotentials our numerical techniques were powerful enough only to yield solutions in a range nearT=0 not extending up toTλ. The appropriateness of the model to account for the properties of superfluid helium is discussed and various extensions of our numerical work suggested.