Dense Magnetoplasma Research Articles

Interparticle interaction in spin-aligned and spin-degenerate exciton systems and magnetoplasmas in II-VI quantum wells.

Magnetoluminescence studies of highly excited undoped CdTe/${\mathrm{Cd}}_{0.88}$${\mathrm{Mn}}_{0.12}$Te and ${\mathrm{Cd}}_{0.97}$${\mathrm{Mn}}_{0.03}$Te/${\mathrm{Cd}}_{0.75}$${\mathrm{Mg}}_{0.25}$Te quantum wells (QW's) have been carried out in magnetic fields up to 14 T at 4.2 K. Qualitatively different excitonic systems, spin aligned in (Cd,Mn)Te QW and spin depolarized in CdTe QW, have been generated. The interaction of spin-aligned excitons are found to be weakly repulsive. In contrast, an additional well pronounced emission line M has been found to appear at approximately 5 meV below the excitonic line in the spectra of the spin-degenerate system. This line is assigned to the emission of excitonic molecules consisting of excitons with different spins. Finally, we have shown that the renormalization of Landau-level transitions in dense electron-hole magnetoplasmas with several occupied Landau levels depends on their spin state, it is markedly weaker in the spin-polarized plasmas. \textcopyright{} 1996 The American Physical Society.

Renormalization effects in dense neutral magnetoplasma photoexcited in CdTe/CdMnTe quantum wells

AbstractAn optical study of the dense neutral electron‐hole magnetoplasma is carried out in an undoped CdTe/Cd0.88Mn0.12Te quantum well in magnetic fields up to 14 T at 2 K. The renormalization of the Landau‐level transition energies is found to be qualitatively similar to that in magnetoplasmas photoexcited in the InGaAs/GaAs quantum wells, but to differ quantitatively. The difference appears due to the enhanced Coulomb interaction and electron‐phonon coupling in CdTe quantum wells.

Renormalization effects in the dense neutral magnetoplasma of quantum wells with two filled subbands.

Optical studies of the neutral electron-hole (eh) magnetoplasma in undoped $\frac{{\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}}{\mathrm{GaAs}}$ quantum wells (QW's) have been performed in magnetic fields up to 12 T. Three experimental situations were investigated over a wide range of plasma densities with subband splittings that were smaller, slightly larger, and much larger than the cyclotron energy. For dense (${n}_{\mathrm{eh}}\ensuremath{\approx}5\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$) and hot ($T\ensuremath{\approx}200\ensuremath{-}300$ K) photoexcited plasmas, the zeroth Landau-level (LL) transition energies of both sub-bands are in agreement with results of random-phase-approximation calculations neglecting excitonic effects. The stronger renormalization of the first subband is mainly due to the difference in the screened exchange contribution to the renormalization of the band gap. Excitonic corrections become important with decreasing density. They appear first near the Fermi edge and influence the initial or the final state of the optical transitions, depending on the filling of the corresponding LL's. In narrow QW's they lead to a much stronger renormalization of the zeroth LL in the second subband. The excitonic effects decrease with increasing QW width and decreasing magnetic field. At 4 T and a QW width of 30 nm they are negligible already at ${n}_{\mathrm{eh}}\ensuremath{\approx}5\ifmmode\times\else\texttimes\fi{}{10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}2}$. In this case, the strong difference between the renormalization of the zeroth and the first LL observed at small plasma densities is connected with the much smaller binding energy of the $2s$ magnetoexcitons in the empty QW.

Renormalization effects in the dense electron-hole magnetoplasma of a strained InxGa1-xAs/GaAs single quantum well after picosecond excitation.

The renormalization of the Landau-level transition energies in the dense quasi-two-dimensional magnetoplasma has been determined from time-resolved luminescence spectra in a strained undoped ${\mathrm{In}}_{0.17}$${\mathrm{Ga}}_{0.83}$As/GaAs quantum well. The neutral electron-hole magnetoplasma was created by 1-ps laser pulses in magnetic fields H\ensuremath{\le}7.5 T. The renormalization has been found to depend strongly not only on the carrier density but also on their distribution over Landau levels. The dependence is explained by the interplay of the attractive exchange and repulsive Pauli contributions in the transition energies and Coulomb interaction screening effect.

Magnetoluminescence study of many-body effects in a dense electron-hole plasma of strained InxGa1-xAs/GaAs quantum wells.

High-excitation luminescence spectra from a highly homogeneous electron-hole system have been investigated in strained undoped ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs quantum wells (QW's) with nearly parabolic conduction and valence bands in magnetic fields H\ensuremath{\le}12 T. The spectra show well pronounced Landau levels which are shifted to lower energy with respect to separately measured magnetoexciton photoexcitation maxima in the empty QW. The shift depends on the carrier density, subband, and Landau-level number. For the dense (${\mathit{n}}_{\mathit{e}\mathrm{\ensuremath{-}}\mathit{h}}$>${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$) magnetoplasma with electron temperature of the order of the cyclotron energy, a simple plasma approximation has been found to describe the Landau-level splitting. The band-gap shrinkage and reduced effective-mass ${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}1}$=${\mathit{m}}_{\mathit{e}}^{\mathrm{\ensuremath{-}}1}$+${\mathit{m}}_{\mathit{e}}^{\mathrm{\ensuremath{-}}1}$ renormalization have been carefully measured and compared with those in the unstrained ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As/InP QW's. The difference has been revealed in the reduced effective-mass renormalization connected with renormalization of ${\mathit{m}}_{\mathit{h}}$ due to the change of the light-hole--heavy-hole subband splitting.

Excitons in dense two-dimensional electron-hole magnetoplasmas.

We report clear excitonic effects in the optical spectra of neutral, dense magnetoplasmas in an ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As/InP quantum well at low temperatures. The observed suppression of the density dependence of the uppermost occupied (${\mathit{j}}_{\mathit{e}}$=${\mathit{j}}_{\mathit{h}}$=N) Landau-level transition energies in the range of filling factors N/2N+1 is direct evidence that electrons and holes from the Nth Landau levels bind into magnetoexcitons. The effect disappears with increasing temperature. Good agreement between experimental results and theoretical calculations is obtained by including both the inter-Landau-level coupling and screening effects.

Excitonic Effects in Neutral Electron–Hole Magnetoplasma in Quantum Wells at Low Temperature

AbstractHigh excitation luminescence spectra from a homogeneous electron–hole system are investigated in undoped unstrained InxGa1−xAs/InP quantum wells in magnetic fields up to 12 T. Clear excitonic effects are observed in the optical spectra of neutral, dense magnetoplasmas at low temperatures. These appear as the suppression of the density dependence of transition energies between the uppermost occupied (Je = jh = N) Landau levels in the range of filling factors N < v/2 < N + 1. The effect disappears with increasing temperature. The experimental results are in agreement with theoretical calculations including both the inter‐Landau‐level coupling and screening effects. In a magnetoplasma with an integer filling factor, Landau‐level transitions near the Fermi level are well described in terms of excitons and deexcitons.

On the excitation of cyclotron harmonic waves by newborn heavy ions

Wave measurements in planetary foreshocks and cometary environments show the sporadic occurrence of magnetic spectra with harmonic structure related to ion cyclotron frequencies. Dilute populations of anisotropic and/or drifting charged particles can excite obliquely propagating modes with spacecraft frequencies close to the observed harmonics. We extend previous analyses of this generation mechanism to drifting and nondrifting loss‐cone type distributions of heavy ions in a dense hydrogen magnetoplasma, characterizing the complex (real frequency and growthrate) dispersion, polarization and compressibility of the unstable cyclotron harmonic waves. Solution of the full kinetic dispersion equation shows that it is possible to attain harmonic excitation, both in the drifting and nondrifting regimes. However, the bandwidth inherent to frequency Doppler shifts of obliquely propagating waves might preclude the observation of spectral structure in the spacecraft frame. The Giotto observations in the upstream region of comet Halley provide a reference to discuss the results.

Antenna radiation pattern of cyclotron harmonic waves in a hot magnetoplasma

The near and far field radiation pattern of a very short antenna is studied in the plasma regime. ωc < ω < 2ωc, ωp ≫ ωc (where ωp and ωc are the electron plasma and cyclotron frequencies, respectively). The experiment is performed in a large laboratory magnetoplasma. Cyclotron harmonic waves are detected in all directions, not only those corresponding to the purely perpendicular direction of detection as was observed previously. This new result is theoretically explained and studied in detail. Constant phase curves deduced from the dispersion relation for a hot Maxwellian electron magnetoplasma are considered. They are found to be described by the low damped part of the polar dispersion curves. The different shapes of the wave surfaces (convex and concave with respect to the excitation source) are in good agreement with experimental results. The effects of plasma and magnetic field inhomogeneities on the dispersion relation are discussed. Experimental isoamplitude curves are presented in the whole space around the transmitter. The theoretical dispersion curves show that the energy of the cyclotron harmonic waves tend to propagate principally outside a cone whose apex is the transmitter and whose axis is parallel to the direction of the magnetic field. The theoretical opening angle of this cone is given by the direction of the group velocity at the inflexion point of the polar dispersion curve where the Landau damping increases suddenly. This theoretical result is in reasonable agreement with the spatial distribution of energy observed experimentally. From this study it is shown that the simple dispersion relation for perpendicular propagation can be used to predict qualitatively the distribution of cyclotron harmonic waves in all directions for dense magnetoplasma conditions.