Phase diagram of microcavity exciton-polariton condensates

In this work, we study the exciton-polariton condensate phase transition in a microcavity matter-light system in which electron-hole Coulomb interaction and matter-light coupling effects are treated on an equal footing. In the framework of the unrestricted Hartree-Fock approximation applying the two-dimensional exciton-polariton model, we derive the self-consistent equations determining simultaneously the excitonic and the photonic condenstate order parameters. In the thermal equilibrium limit, we find a condensed state of the exciton-polariton systems and phase diagrams are then constructed. At a given low temperature, the condensate by its nature shows a crossover from an excitonic to a polaritonic and finally photonic condensed state as the excitation density increases at large detuning. Without the detuning, the excitonic condensed state disappears whereas the polaritonic or photonic phases dominate. The crossover is also found by lowering the Coulomb interaction at a finite matter-light coupling. Lowering the Coulomb interaction or increasing the temperature, the excitonic Mott transition occurs, at which the exciton-polariton condensates dissociate to free electron-hole/photon. Depending on temperature and excitation density, the phase transition of the exciton-polariton condensates is also addressed in signatures of photoluminescence mapping to the photonic momentum distribution.Comment: 7 pages, 6 figure

Magnetophonon Resonance in Quantum Wells with Parabolic Potential

The linear dc magnetoconductivity in the$(x,y)$ plane of a parabolic quantum well, with a magnetic field$\vec B = B\vec e_z$ applied, is evaluated for electron - opticalphonon interaction. For nonpolar optical and polar optical phonons,the magneto-conductivity oscillates as a function of the magneticfield with resonances occurring when $P\omega_c=\omega_0$, where$\omega_c$ and $\omega_0$ are cyclotron frequency and optical phononfrequency, respectively, and where $P$ is an integer. The analyticresults are numerically evaluated to show explicitly the dependenceof magneto-conductivity on the magnetic field, the confinementfrequency in $z$ direction, and the temperature of the system

Hall Effect on the Doped Semiconductor Superlattice with an In-plane Magnetic Field Under Influence of an Intense Electromagnetic Wave

The Hall effect is studied theoretically in a doped semiconductor superlattice (DSSL) subjected to a crossed dc electric field and magnetic field in the presence of an intense electromagnetic wave (EMW). By using the quantum kinetic equation for electrons interacting with acoustic phonons at low temperature, we obtain expressions for the magnetoresistance as well as the Hall coefficient in dependence on the external fields and characteristic parameters of the DSSL. Analytical results are numerically evaluated for the GaAs:Si/GaAs:Be DSSL. The dependence of the magnetoresistance on the magnetic field is consistent with the result obtained for some two-dimensional electron systems. The Hall coefficient depends weakly on the magnetic field and its value in the presence of the EMW is smaller than that of the case without EMW

Magneto-transport properties of monolayer borophene in perpendicular magnetic field: influence of electron-phonon interaction

The magneto-transport properties of a borophene monolayer in a perpendicular magnetic field B are studied via calculating the conductivity tensor and resistance under electron-optical phonon interaction by using the linear response theory. Numerical results are obtained and discussed for some specific parameters. The magnetic field-dependent longitudinal conductivity shows the magneto-phonon resonance effect that describes the transition of electrons between Landau levels by absorbing/emitting an optical phonon. The Hall conductivity increases first and then decreases with the magnetic field strength. Also, the longitudinal resistance increases significantly with increasing temperature, which shows the metal behaviour of the material. Practically, the observed magneto-phonon resonance can be applied to experimentally determine some material parameters, such as the distance between Landau levels and the optical phonon energy

Zeeman-magnetic-field–induced magnetic phase transition in doped armchair boron-nitride nanoribbons

In this work, the magneto-charge structure factor (CSF) of hexagonal doped armchair boron-nitride nanoribbons (ABNNRs) has been addressed using the tight-binding Hamiltonian model and the Green's function technique. In particular, we study the charge static susceptibility in the presence of the Zeeman magnetic field. The calculations of the correlation function of charge densities lead to magnetic phase transitions, which are explained by the temperature-dependent magneto-CSF. We have observed different width-dependent CSF treatments in the presence and absence of magnetic field for both undoped and doped ABNNRs. Depending on the magnetic field strength, transitions from antiferromagnetic to the ferromagnetic (paramagnetic) arrangement of spins has been established for undoped (doped) ABNNRs. We have found that, furthermore, in addition to the magnetic field, the magnetic phase can be controlled by the concentration and incoming momentum of electronic dopants. These results have direct implications for the control of the dopant and magnetic field for the practical realization of boron-nitride nanoribbons-based spintronic applications

Phonon effects in the excitonic condensation induced in the extended Falicov-Kimball model

A ground state of the excitonic condensate in the 2D extended Falicov-Kimball model involving the coupling of electrons and vibrational degrees of freedom has been investigated. Adapting the unrestricted Hartree-Fock approximation, we have derived a set of explicitly self-consistent equations determining both an excitonic order parameter and a lattice distortion when both the electron-phonon coupling and the electron-electron interaction are treated on an equal footing. A ground-state phase diagram of the excitonic condensate depending on the model parameters is constructed. The phase diagram shows us that a window of the excitonic condensate with lattice distortion increases when increasing the electron-phonon coupling or moving up the f-electron level, whereas, it is confined in between two critical values of the Coulomb interaction. The Coulomb interaction and the electron-phonon coupling have been affirmed to act together in establishing the excitonic condensate phase with lattice distortion in dichalcogenide systems. The BCS-BEC crossover of the excitonic condensation in the systems is also addressed