Two-dimensional cavity polaritons under the influence of the perpendicular strong magnetic and electric fields. The gyrotropy effects

The properties of the two-dimensional cavity polaritons subjected to the action of a strong perpendicular magnetic and electric fields, giving rise to the Landau quantization (LQ) of the 2D electrons and holes accompanied by the Rashba spin-orbit coupling, by the Zeeman splitting and by the nonparabolicity of the heavy-hole dispersion law are investigated. We use the method proposed by Rashba [1] and the obtained results are based on the exact solutions for the eigenfunctions and for the eigenvalues of the Pauli-type Hamilonians with third order chirality terms and nonparabolic dispersion law for heavy-holes and with the first order chirality terms for electrons. The selection rules of the band-to-band optical quantum transitions as well as of the quantum transitions from the ground state of the crystal to the magnetoexciton states depend essentially on the numbers $n_{e}$ and $n_{h}$ of the LQ levels of the (e-h) pair forming the magnetoexciton. It is shown that the Rabi frequency $\Omega_{R}$ of the polariton branches and the magnetoexciton oscillator strength $f_{osc}$ increase with the magnetic field strength $B$ as $\Omega_{R}\sim \sqrt{B}$, and $f_{osc}\sim B$. The optical gyrotropy effects may be revealed changing the sign of the photon circular polarization at a given sign of the wave vector longitudinal projection $k_{z}$ or eqivalently changing the sign of $k_{z}$ at the same selected circular polarization.Comment: 7 pages, 1 figure. To be published Solid State Com

Metastable bound states of the two-dimensional bi-magnetoexcitons in the lowest Landau levels approximation

The possible existence of the bound states of the interacting two-dimensional (2D) magnetoexcitons in the lowest Landau levels (LLLs) approximation was investigated using the Landau gauge description. The magnetoexcitons taking part in the formation of the bound state with resultant wave vector k= 0 have opposite in-plane wave vectors and look as two electric dipoles with the arms oriented in-plane perpendicularly to the corresponding wave vectors. The bound state of two antiparallel dipoles moving with equal probability in any direction of the plane with equal but antiparallel wave vectors is characterized by the variational wave function of the relative motion depending on the modulus | k |. The spins of two electrons and the effective spins of two holes forming the bound states were combined separately in the symmetric or in the antisymmetric forms for electrons and holes. In the case of the variational wave function the maximum density of the magnetoexcitons in the momentum space representation is concentrated on the in-plane ring. The stable bound states of the bimagnetoexciton molecule do not exist for both spin orientations. Instead of them, a deep metastable bound state with the activation barrier comparable with the ionization potential of the magnetoexciton with k =0 was revealed.Comment: 13 pages, 4 figure

Landau quantization, Rashba spin-orbit coupling and Zeeman splitting of two-dimensional heavy holes

The origin of the g-factor of the two-dimensional (2D) electrons and holes moving in the periodic crystal lattice potential with the perpendicular magnetic and electric fields is discussed. The Pauli equation describing the Landau quantization accompanied by the Rashba spin-orbit coupling (RSOC) and Zeeman splitting (ZS) for 2D heavy holes with nonparabolic dispersion law is solved exactly. The solutions have the form of the pairs of the Landau quantization levels due to the spinor-type wave functions. The energy levels depend on amplitudes of the magnetic and electric fields, on the g-factor {g-h}, and on the parameter of nonparabolicity C. The dependences of two energy levels in any pair on the Zeeman parameter {Z_h}={g_h}{m_h}/4{m_0}, where {m_h} is the hole effective mass, are nonmonotonous and without intersections. The smallest distance between them at C=0 takes place at the value {Z_h}=n/2, where n is the order of the chirality terms determined by the RSOC and is the same for any quantum number of the Landau quantization.Comment: 20 pages, 6 figure

The Influence of the Rashba spin orbit coupling on the two dimensional magnetoexcitons

Cataloged from PDF version of article.The influence of the Rashba spin-orbit coupling (RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba (1960 Fiz. Tverd. Tela 2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field

Ear, nose and throat injuries at Bugando Medical Centre in northwestern Tanzania: a five-year prospective review of 456 cases.

Injuries to the ear, nose and throat (ENT) regions are not uncommon in clinical practice and constitute a significant cause of morbidity and mortality in our setting. There is dearth of literature on this subject in our environment. This study was conducted to describe the causes, injury pattern and outcome of these injuries in our setting and proffer possible preventive measures. This was a descriptive prospective study of patients with ear, nose and throat injuries managed at Bugando Medical Centre between May 2007 and April 2012. Ethical approval to conduct the study was sought from relevant authorities. Statistical data analysis was performed using SPSS computer software version 17.0. A total of 456 patients were studied. The median age of patients at presentation was 18 years (range 1 to 72 years). The male to female ratio was 2:1. The commonest cause of injury was foreign bodies (61.8%) followed by road traffic accidents (22.4%). The ear was the most common body region injured accounting for 59.0% of cases. The majority of patients (324, 71.1%) were treated as an outpatient and only 132(28.9%) patients required admission to the ENT wards after definitive treatment. Foreign body removal and surgical wound debridement were the most common treatment modalities performed in 61.9% and 16.2% of cases respectively. Complication rate was 14.9%. Suppurative otitis media (30.9%) was the commonest complication in the ear while traumatic epistaxis (26.5%) and hoarseness of voice (11.8%) in the aero-digestive tract were commonest in the nose and throat. The overall median length of hospital stay for in-patients was 8 days (range 1 to 22 days). Patients who developed complications and those who had associated injuries stayed longer in the hospital (P < 0.001).Mortality rate related to isolated ENT injuries was 1.3% (6 deaths). The majority of patients (96.9%) were treated successfully and only 3.1% of cases were discharged with permanent disabilities. Injuries to the ENT regions are not uncommon in our environment and foreign bodies constitute a significant cause of injury. Majority of these injuries can be prevented through public enlightenment campaigns

Nonlinear equation for curved stationary flames

A nonlinear equation describing curved stationary flames with arbitrary gas expansion $\theta = \rho_{{\rm fuel}}/\rho_{{\rm burnt}}$, subject to the Landau-Darrieus instability, is obtained in a closed form without an assumption of weak nonlinearity. It is proved that in the scope of the asymptotic expansion for $\theta \to 1,$ the new equation gives the true solution to the problem of stationary flame propagation with the accuracy of the sixth order in $\theta - 1.$ In particular, it reproduces the stationary version of the well-known Sivashinsky equation at the second order corresponding to the approximation of zero vorticity production. At higher orders, the new equation describes influence of the vorticity drift behind the flame front on the front structure. Its asymptotic expansion is carried out explicitly, and the resulting equation is solved analytically at the third order. For arbitrary values of $\theta,$ the highly nonlinear regime of fast flow burning is investigated, for which case a large flame velocity expansion of the nonlinear equation is proposed.Comment: 29 pages 4 figures LaTe