Theory of combined exciton-cyclotron resonance in a two-dimensional electron gas: The strong magnetic field regime

I develop a theory of combined exciton-cyclotron resonance (ExCR) in a low-density two-dimensional electron gas in high magnetic fields. In the presence of excess electrons an incident photon creates an exciton and simultaneously excites one electron to higher-lying Landau levels. I derive exact ExCR selection rules that follow from the existing dynamical symmetries, magnetic translations and rotations about the magnetic field axis. The nature of the final states in the ExCR is elucidated. The relation between ExCR and shake-up processes is discussed. The double-peak ExCR structure for transitions to the first electron Landau level is predicted.Comment: 5 pages, 3 figures, replaced with the published versio

Internal Transitions of Two-Dimensional Charged Magneto-Excitons X-: Theory and Experiment

Internal spin-singlet and spin-triplet transitions of charged excitons X- in magnetic fields in quantum wells have been studied experimentally and theoretically. The allowed X- transitions are photoionizing and exhibit a characteristic double-peak structure, which reflects the rich structure of the magnetoexciton continua in higher Landau levels (LL's). We discuss a novel exact selection rule, a hidden manifestation of translational invariance, that governs transitions of charged mobile complexes in a magnetic field.Comment: 4 pages, 2 figures, submitted to Physica

Shake-up Processes in a Low-Density Two-Dimensional Electron Gas: Spin-Dependent Transitions to Higher Hole Landau Levels

A theory of shake-up processes in photoabsorption of an interacting low-density two-dimensional electron gas (2DEG) in strong magnetic fields is presented. In these processes, an incident photon creates an electron-hole pair and, because of Coulomb interactions, simultaneously excites one particle to higher Landau levels (LL's). In this work, the spectra of correlated charged spin-singlet and spin-triplet electron-hole states in the first hole LL and optical transitions to these states (i.e., shake-ups to the first hole LL) are studied. Our results indicate, in particular, the presence of optically-active three-particle quasi-discrete states in the exciton continuum that may give rise to surprisingly sharp Fano resonances in strong magnetic fields. The relation between shake-ups in photoabsorption of the 2DEG and in the 2D hole gas (2DHG), and shake-ups of isolated negative X^- and positive X^+ trions are discussed.Comment: 8 pages, 8 figures. References updated, one figure added (Fig. 6). Accepted in Phys. Rev.

Charged mobile complexes in magnetic fields: A novel selection rule for magneto-optical transitions

The implications of magnetic translations for internal optical transitions of charged mobile electron-hole ($e$--$h$) complexes and ions in a uniform magnetic field $B$ are discussed. It is shown that transitions of such complexes are governed by a novel exact selection rule. Internal intraband transitions of two-dimensional (2D) charged excitons $X^-$ in strong magnetic fields are considered as an illustrative example.Comment: 4 pages, 2 figure

Definitive observation of the dark triplet ground state of charged excitons in high magnetic fields

The ground state of negatively charged excitons (trions) in high magnetic fields is shown to be a dark triplet state, confirming long-standing theoretical predictions. Photoluminescence (PL), reflection, and PL excitation spectroscopy of CdTe quantum wells reveal that the dark triplet trion has lower energy than the singlet trion above 24 Tesla. The singlet-triplet crossover is "hidden" (i.e., the spectral lines themselves do not cross due to different Zeeman energies), but is confirmed by temperature-dependent PL above and below 24 T. The data also show two bright triplet states.Comment: 4 figure

Spin Relaxation in a Quantized Hall Regime in Presence of a Disorder

We study the spin relaxation (SR) of a two-dimensional electron gas (2DEG) in the quantized Hall regime and discuss the role of spatial inhomogeneity effects on the relaxation. The results are obtained for small filling factors ($\nu\ll 1$) or when the filling factor is close to an integer. In either case SR times are essentially determined by a smooth random potential. For small $\nu$ we predict a "magneto-confinement" resonance manifested in the enhancement of the SR rate when the Zeeman energy is close to the spacing of confinement sublevels in the low-energy wing of the disorder-broadened Landau level. In the resonant region the $B$-dependence of the SR time has a peculiar non-monotonic shape. If $\nu\simeq 2n+1$, the SR is going non-exponentially. Under typical conditions the calculated SR times range from $10^{-8}$ to $10^{-6}$s.Comment: 10 pages, 1 figure. To appear in JETP Letter

Internal transitions of quasi-2D charged magneto-excitons in the presence of purposely introduced weak lateral potential energy variations

Optically detected resonance spectroscopy has been used to investigate effects of weak random lateral potential energy fluctuations on internal transitions of charged magneto-excitons (trions) in quasi two-dimensional GaAs/AlGaAs quantum-well (QW) structures. Resonant changes in the ensemble photoluminescence induced by far-infrared radiation were studied as a function of magnetic field for samples having: 1) no growth interrupts (short range well-width fluctuations), and 2) intentional growth interrupts (long range monolayer well-width differences). Only bound-to-continuum internal transitions of the negatively charged trion are observed for samples of type 1. In contrast, a feature on the high field (low energy) side of electron cyclotron resonance is seen for samples of type 2 with well widths of 14.1 and 8.4 nm. This feature is attributed to a bound-to-bound transition of the spin-triplet with non-zero oscillator strength resulting from breaking of translational symmetry.Comment: 16 pages, 3 figures, submitted to Physical Review

Improvement of Research Competencies of School Teachers in Context of Modernization of National Education

The questions of improvement of research competences of a school teacher are considered. The competences of a teacher-researcher are interpreted as developing professional and personal properties with a complex structure, the elements of which are focused on the implementation of the functions of the research activities of a school teacher; they are integral and integrative; they contribute to self-development of a teacher in the chosen field of activity and the realization of his / her potential; form conditions to search for new information required in the resolution of difficult situations at a specific school according to the goals and objectives of the contemporary general education. The relevance of this article is associated with the increasing requirements imposed by society to the research activities of a modern school teacher. Areas of application of professional efforts are defined, where the research potential of a teacher is manifested most actively: the area of analysis, synthesis and mastering innovative pedagogical experience; field of popularization and initial practical use of innovative pedagogical experience and advanced developments; area of improvement of professional skills and disclosure of the creative potential of a teacher; area of innovative processes in the education system. Four levels of development of the research competences available to the school teacher are established: basic, empirical (locally-initiative), productive (tactical) and constructive (strategic) for which different degree of development of research competences is characteristic. The technology of improving the research competences of a school teacher is proposed, which includes four stages: motivational-target, theoretical, design, practical, control and remedial

Goldstone Mode Relaxation in a Quantum Hall Ferromagnet due to Hyperfine Interaction with Nuclei

Spin relaxation in quantum Hall ferromagnet regimes is studied. As the initial non-equilibrium state, a coherent deviation of the spin system from the ${\vec B}$ direction is considered and the breakdown of this Goldstone-mode state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring non-exponentially with time is studied in terms of annihilation processes in the "Goldstone condensate" formed by "zero spin excitons". The relaxation rate is calculated analytically even if the initial deviation is not small. This relaxation channel competes with the relaxation mechanisms due to spin-orbit coupling, and at strong magnetic fields it becomes dominating.Comment: 8 page

Detecting the (Quasi-)Two-Body Decays of τ\tau Leptons in Short-Baseline Neutrino Oscillation Experiments

Novel detector schemes are proposed for the short-baseline neutrino experiments of next generation, aimed at exploring the large-$\Delta m^2$ domain of \omutau oscillations in the appearance mode. These schemes emphasize good spectrometry for charged particles and for electromagnetic showers and efficient reconstruction of \ypi_gg decays. The basic elements are a sequence of relatively thin emulsion targets, immersed in magnetic field and interspersed with electronic trackers, and a fine-grained electromagnetic calorimeter built of lead glass. These elements act as an integral whole in reconstructing the electromagnetic showers. This conceptual scheme shows good performance in identifying the $\tau$ (quasi-)two-body decays by their characteristic kinematics and in selecting the electronic decays of the $\tau$.Comment: 34 pages, 8 figure