Localized collective excitations in doped graphene in strong magnetic fields

We consider collective excitations in graphene with filled Landau levels (LL’s) in the presence of an external potential due to a single charged donor D+ or acceptor A− impurity. We show that localized collective modes split off the magnetoplasmon continuum and, in addition, quasibound states are formed within the continuum. A study of the evolution of the strengths and energies of magneto-optical transitions is performed for integer filling factors ν=1,2,3,4 of the lowest LL. We predict impurity absorption peaks above as well as below the cyclotron resonance. We find that the single-particle electron-hole symmetry of graphene leads to a duality between the spectra of collective modes for the D+ and A−. The duality shows up as a set of the D+ and A− magnetoabsorption peaks having the same energies but active in different circular polarizations

Shake-up Processes in Intersubband Magneto-photoabsorption of a Two-Dimensional Electron Gas

I theoretically study shake-up processes in photoabsorption of an interacting low-density two-dimensional electron gas (2DEG) in magnetic fields. Such processes, in which an incident photon creates an electron-hole pair and simultaneously excites one electron to one of the higher Landau levels, were observed experimentally [D.R. Yakovlev et al., Phys. Rev. Lett. 79, 3974 (1997)] and were called combined exciton-cyclotron resonance (ExCR). The recently developed theory of ExCR [A.B. Dzyubenko, Phys. Rev. B 64, 241101 (2001)] allows for a consistent treatment of the Coulomb correlations, establishes the exact ExCR selection rules, and predicts the high field features of ExCR. In this work, I generalize the existing theory of high-field ExCR in the 2DEG to the case when the hole is excited to higher hole Landau levels.Comment: 4 pages, 3 figures; Proceedings NGS-11 (June 2003, Buffalo, NY, USA

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

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

Many-body effects in Landau levels: Non-commutative geometry and squeezed correlated states

We discuss symmetry-driven squeezing and coherent states of few-particle systems in magnetic fields. An operator approach using canonical transformations and the SU(1,1) algebras is developed for considering Coulomb correlations in the lowest Landau levels.Comment: 3 pages, 2 figures; to be reported at 17th Int. Conf. on High Magnetic Fields in Semiconductor Physics, Wuerzburg, Germany, July 30 - Aug 4, 200

Double-exciton component of the cyclotron spin-flip mode in a quantum Hall ferromagnet

We report on the calculation of the cyclotron spin-flip excitation (CSFE) in a spin-polarized quantum Hall system at unit filling. This mode has a double-exciton component which contributes to the CSFE correlation energy but can not be found by means of a mean field approach. The result is compared with available experimental data.Comment: 9 pages, 2 figure

Interaction of an electron gas with photoexcited electron-hole pairs in modulation-doped GaAs and CdTe quantum wells

The nature of the correlated electron gas and its response to photo-injected electron-hole pairs in nominally undoped and modulation-doped multiple quantum-well (MQW) structures was studied by experiment and theory, revealing a new type of optically-active excitation, magnetoplasmons bound to a mobile valence hole. These excitations are blue-shifted from the corresponding transition of the isolated charged magnetoexciton X-. The observed blue-shift of X- is larger than that of two-electron negative donor D-, in agreement with theoretical predictions.Comment: 4 pages, 3 figures, EP2DS-14 manuscript, to be published in Physica