Manifestation of collective effects in polarization-resolved recombination spectra of the completely filled zeroth landau level of two-dimensional electrons

The luminescence spectra due to recombination of two-dimensional electrons with optically excited holes have been studied in a wide range of electron filling factors in the transverse magnetic field. A nonmonotonic filling-factor dependence of the energy splitting between different circular polarizations of photoluminescence from the completely filled zeroth Landau level of electrons has been observed. It has been shown that this dependence is associated with collective (excitonic) effects that appear due to the interaction between electrons from partially occupied upper Landau levels and holes remaining on the zeroth Landau level after recombination.     

Manifestation of collective effects in polarization-resolved recombination spectra of the completely filled zeroth landau level of two-dimensional electrons

JETP Letters - The luminescence spectra due to recombination of two-dimensional electrons with optically excited holes have been studied in a wide range of electron filling factors in the...     

Excitonic effects in the recombination radiation spectra of completely filled Landau levels of two-dimensional electrons

The recombination radiation spectra of two-dimensional electrons in an asymmetrically doped GaAs/AlGaAs quantum well are investigated at different temperatures and laser-excitation energies. At low temperatures and in high magnetic fields the recombination lines of the electrons from completely filled Landau levels are split into narrow sublevels. It is shown that this fine structure of the Landau levels is due to the presence of excitonic effects in the initial and final states of the photoexcited system. It is demonstrated that the recombination process is accompanied by the excitation of intersubband and cyclotron magnetoplasma modes. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 38–43 (10 January 1997)     

Anomalous fluctuations of 2D-electron recombination radiation intensity in the quantum Hall regime

Anomalous intensity fluctuations are observed in the spectrum of radiative ecombination of quasi-two-dimensional (2D) electrons with photoexcited holes in a single quantum well. The fluctuations are observed exclusively under the conditions of the quantum Hall effect (QHE). It is shown that, if the QHE conditions are not fulfilled, the radiation intensity fluctuates strictly following the Poisson distribution 〈δN ²〉/〈N〉= 1), whereas in the QHE regime the fluctuation amplitude increases by several orders of magnitude (〈δ N ²〉/〈N〉～10²). It is demonstrated that the maxima of the emission noise amplitude coincide with the maxima of inverse magnetoresistance of 2D electrons in the QHE regime and correspond to establishing an anomalously high uniformity of the system.     

Dissociative recombination of electrons and O 2 + molecular ions in the field of intense visible laser radiation

We analyze the low-temperature dissociative recombination reaction e ^?+O ₂ ⁺ → O(¹ D)+O(³ P) in the field of visible monochromatic laser radiation. The analysis is performed in terms of the multichannel quantum defect theory using the stationary formalism of the radiative collision matrix. We calculate the dependences of the reaction cross section on the incident electron energy, the external electromagnetic field strength and frequency, and also the angle between the directions of the electron beam and the electric vector for linearly polarized radiation. The cross section is shown to increase by several orders of magnitude for a certain choice of these parameters, suggesting the possible laser stimulation of this reaction.     

Synchrotron radiation intensity and energy of runaway electrons in EAST tokamak

A detailed analysis of the synchrotron radiation intensity and energy of runaway electrons is presented for the Experimental Advanced Superconducting Tokamak(EAST). In order to make the energy of the calculated runaway electrons more accurate, we take the Shafranov shift into account. The results of the analysis show that the synchrotron radiation intensity and energy of runaway electrons did not reach the maximum at the same time. The energy of the runaway electrons reached the maximum first, and then the synchrotron radiation intensity of the runaway electrons reached the maximum.We also analyze the runaway electrons density, and find that the density of runaway electrons continuously increased. For this reason, although the energy of the runaway electrons dropped but the synchrotron radiation intensity of the runaway electrons would continue rising for a while.     

Giant fluctuations of radiation intensity of two-dimensional electrons in double quantum wells

Giant fluctuations of the recombination-radiation intensity of two-dimensional electrons were studied in double quantum wells with different well and barrier widths in the regime of the integer quantum Hall effect. It was found that the giant fluctuations of photoluminescence intensity in double quantum wells with a narrow barrier (l<150 Å) occur in a narrow magnetic-field interval, where the sum of electron concentrations in both wells corresponds to the integer filling factors 4, 8, and 12. It was established that, under these conditions, the coefficient C₁₂ of correlation between the radiation intensities from different wells is close to unity. It is shown that, as the barrier width increases (l>200 Å), the coefficient C₁₂ decreases, changes sign, and goes to zero at l=400 Å.     

Theory of the spectral acoustic phonon emission intensity of hot 2D electrons in quantized n-inversion layers

The spectral acoustic phonon emission intensity of the hot quasi two-dimensional electron gas (2DEG) in quantized n-Si (GaAs) inversion layers is calculated as a function of the phonon angular frequency w at different values of the carrier temperature T_e and density N_s. In the long wave length limit (ℏw ⪡ k_BT_e) the emission intensity increases ∝ w^s(w^s+1) for bulk- (surface-) modes where s = 3 for the unscreened acoustic deformation potential coupling. At w ≈ v_j2k_F (v_j: sound velocity of the phonon mode j, k_F: radius of the Fermi-circle) the emission intensity reaches a maximum whose position is shifted to higher w-values if N_s increases. For given values of N_s, T_e, T (lattice temperature) and ϑ (emission angle) the emission intensity maximum of the n-GaAs inversion layer is found to be about one order of magnitude smaller than the intensity maximum of the n-Si inversion layer.     

Giant fluctuations in the radiation intensity of two-dimensional electrons under quantum hall effect conditions

Giant fluctuations in the 2D-electron recombination radiation were studied in structures with a single or double GaAs quantum well under quantum Hall effect conditions. It is established that, if these conditions are exactly satisfied, the amplitude of the 2D-electron photoluminescence (PL) intensity is several orders of magnitude higher than the noise level, with the noise having a normal (Poisson) distribution. The fluctuations in the PL line intensity are accompanied by a jumpwise change in the line positions. Analogous jumps were also observed in the spectra of inelastic light scattering by 2D electrons in structures with a single GaAs quantum well. The fluctuation processes are correlated over macroscopic distances. The characteristic correlation length is 1–2 mm. The spectral density of giant fluctuations was found to exhibit narrow peaks. The ratios of the frequencies of these peaks are equal to those of Fibonacci numbers. The appearance of such frequencies in the fluctuation spectrum indicates that the fluctuations studied bear a resemblance to processes occurring in open dissipative dynamic systems. The methods developed in the theory of these systems can, in principle, be used to study giant fluctuations.     

Channel mixing effects in the dissociative recombination of H+3 with slow electrons

We discuss the low-energy dissociative recombination of H+3, which strongly influences the abundance of this ion in diffuse interstellar molecular clouds. The kinetic couplings between the ionization continuum and the dissociative ground state of H3 have been used as input to a two-dimensional wave packet calculation of dissociation dynamics. The cross section obtained for direct dissociative recombination is much smaller than the latest experimental results. However, a multichannel quantum defect treatment shows that an indirect mechanism via bound Rydberg states of H3 prevails for this process.     

Manifestation of electrification effects in study of radiation optical properties of glasses

The change in optical transmission of specimens of K-208 glass under the action of an electron flux is studied experimentally as a function of electrification conditions. The kinetics of darkening of specimens of different thicknesses and the darkening distribution over the surface indicate the effect of radiation electrification of the glass on motion of moderate energy electron fluxes. A model is proposed for a dielectric electrified by irradiation, which explains the dependence of the change in optical properties of the glasses studied on irradiation conditions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 14–17, May, 1986.     

Emission of circularly polarized recombination radiation from p-doped GaAsP bombarded with longitudinally polarized electrons

We report measurements of circularly polarized recombination radiation from a GaAs_0.6P_0.4 crystal bombarded with longitudinally spin polarized electrons of 10 eV energy. Qualitatively, this process can be considered as the inverse of the photoemission utilized in GaAs and GaAsP polarized-electron sources. The measured degree of circular polarization is 0.29%±0.06% if the crystal is cooled with liquid nitrogen and the incident electrons are 15%±3% polarized.     

Spatial correlations of recombination radiation intensities of two-dimensional electrons under the conditions of the quantum Hall effect

Correlations have been studied between the recombination radiation intensities of a two-dimensional electron gas measured at different points of the sample with giant luminescence fluctuations in the quantum Hall effect regime. It has been found that the correlation of the radiation intensities measured under these conditions at different points of the sample separated by a distance of 1–3 mm is close to unity and disappeared in a threshold way with increasing temperature. It is shown that macroscopic spatial correlations also disappear if the electron system is artificially divided into two subsystems not connected with each other.     

The effects of infrared radiation on trapped electrons in excited ZnS-phosphors

By means of rise curves the number of traped electrons in ZnS-phosphors can be determined. The effect of infrared irradiation added simultaneously to UV excitation is that of quenching; in addition the number of occupied traps (n _t) is found to be considerably reduced; approximately in the same ratio as the reduction of light. Since the free electron concentration (n) is also quenched by the addition of infrared to ultraviolet, there is some difficulty with the relationship: Light=constant ×n×n _t.     

Microwave radiation induced magneto-oscillations in the longitudinal and transverse resistance of a two-dimensional electron gas

We confirm the existence of magneto-resistance oscillations in a microwave-irradiated two-dimensional electron gas, first reported in a series of papers by Zudov et al. [Phys. Rev. B 64 (2001) 201311] and Mani et al. [Nature (London) 420 (2002) 646]. In our experiments, on a sample with a moderate mobility, the microwave induced oscillations are observed not only in the longitudinal but also in the transverse-resistance (Hall resistance). The phase of the oscillations is such that the decrease (increase) in the longitudinal resistance is accompanied by an increase (decrease) in the absolute value of the Hall resistance. We believe that these new results provide valuable new information to better understand the origin of this interesting phenomenon.     

激光功率密度对Al膜靶后表面快电子发射的影响

 报道了在20 TW皮秒激光器上完成的p偏振激光与等离子体相互作用过程中产生的快电子的角分布和能谱测量结果。实验得到：当激光功率密度小于10¹⁷ W/cm²时,电子发射没有明显定向性,在激光入射面内多峰发射;当激光功率密度大于10¹⁷ W/cm2,小于10¹⁸ W/cm²时,电子主要沿靶面法线方向发射;当激光功率密度达到相对论强度时,电子主要沿激光传播方向发射;激光功率密度未达到相对论强度时,靶后表面法线方向快电子能谱拟合平均温度符合共振吸收温度定标率;激光功率密度达相对论强度以上时,靶后表面法线方向快电子能谱拟合平均温度高于已有的温度定标率。     

Spectral and total intensity of radiation of relativistic electrons and positrons with planar channeling

The spectral and total intensity of radiation of relativistic electrons and positrons is considered within the framework of a Langevin approach to the theory of transit of fast charged particles across a crystal. It is shown that one of the terms of the total intensity of radiation increases exponentially rapidly along those segments of the path that are in regions in which the potential of the planar channel of the crystal has negative Gaussian curvature. Surgut State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 42–44, September, 1997.