arXiv subjects

A. B. Dzyubenko

Publications and source records attributed to A. B. Dzyubenko.

At least 19 recordsLinked to original sources

arXiv2011

Magnetoplasmons bound to short-range impurities in graphene: Symmetries and optics

We consider a graphene sheet in the presence of a strong perpendicular magnetic field with a single short-range delta-impurity situated at one of the carbon sites. We study the neutral inter-Landau level collective excitations, magnetoplasmons, which become localized on the impurity. Some of these excitations involve a pseudospin flip (intervalley transitions), since the impurity can scatter electrons between the two valleys. We propose a classification of states of the excitations in graphene and introduce the appropriate quantum numbers. The energies and optical strengths of collective excitations are calculated for a range of integer filling factors and impurity strengths. We establish a set of symmetries matching the energies and absorption strengths of collective excitations for different sublattice locations of the impurity, filling factors, circular light polarizations and signs of the impurity potential.

cond-mat.str-el↗

arXiv2009

Localised Magneto-Optical Collective Excitations of Impure Graphene

We study optically-induced collective excitations of graphene in the presence of a strong perpendicular magnetic field and a single impurity. We determine the energies and absorption strengths of these excitations, which become localised on the impurity. Two different types of impurity are considered i. the long-range Coulomb impurity, ii. a delta-function impurity located at either an A or B graphene sublattice site. Both impurity types result in some bound states appearing both above and below the magnetoplasmon continuum, although the effect of the short-range impurity is less pronounced. The dependence of the energies and oscillator strengths of the bound states on the filling factor is investigated.

cond-mat.mes-hall↗

arXiv2009

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 nu = 1, 2, 3, 4 of the lowest LL. We predict impurity absorption peaks above as well as below the cyclotron resonance. We show 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- magneto-absorption peaks having same energies, but active in different circular polarizations.

cond-mat.mes-hall↗

arXiv2007

Interacting like charges in Landau levels: Planar geometry, symmetries, and effective quasiparticles

We consider a system of two interacting particles with like but unequal charges in a magnetic field in the planar geometry. We construct a complete basis of states compatible with both the axial symmetry and magnetic translations. The basis is obtained using a canonical transformation that generates effective quasiparticles with modified interactions. We establish a connection of this transformation with the SU(2) algebra and make use of the SU(2) Baker-Campbell-Hausdorff formulas for evaluating the interaction matrix elements. We calculate analytically the eigenenergies of the problem (Haldane pseudopotentials) in the first few Landau levels for a relatively wide class of interaction potentials.

cond-mat.mes-hall↗

arXiv2006

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.

cond-mat.mes-hall↗

arXiv2006

Optics of charged excitons in quantum wells: Free versus donor-bound complexes

We theoretically study localization of quasi-two-dimensional negatively charged excitons X^- on isolated charged donors in magnetic fields. We consider donors located in a barrier at various distances L from the heteroboundary as well as donors in the quantum well. We establish how many different singlet X_s^- and triplet X_t^- bound states a donor ion D^+ can support in magnetic fields B > 6 T. We find several new bound states, some of which have surprisingly large oscillator strengths.

cond-mat.mes-hall↗

arXiv2005

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.

cond-mat.str-el↗

arXiv2004

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.

cond-mat.mes-hall↗

arXiv2003

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.

cond-mat.mes-hall↗

arXiv2001

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.

cond-mat.mes-hall↗

arXiv2001

Charged two-dimensional magnetoexciton and two-mode squeezed vacuum states

A novel unitary transformation of the Hamiltonian that allows one to partially separate the center-of-mass motion for charged electron-hole systems in a magnetic field is presented. The two-mode squeezed oscillator states that appear at the intermediate stage of the transformation are used for constructing a trial wave function of a two-dimensional (2D) charged magnetoexciton.

cond-mat.mes-hall↗

arXiv2001

Charged hydrogenic problem in a magnetic field: Non-commutative translations, unitary transformations, and coherent states

An operator formalism is developed for a description of charged electron-hole complexes in magnetic fields. A novel unitary transformation of the Hamiltonian that allows one to partially separate the center-of-mass and internal motions is proposed. We study the operator algebra that leads to the appearance of new effective particles, electrons and holes with modified interparticle interactions, and their coherent states in magnetic fields. The developed formalism is used for studying a two-dimensional negatively charged magnetoexciton $X^-$. It is shown that Fano-resonances are present in the spectra of internal $X^-$ transitions, indicating the existence of three-particle quasi-bound states embedded in the continuum of higher Landau levels.

cond-mat.mes-hall↗

arXiv2001

Internal transitions of negatively charged magneto-excitons and many body effects in a two-dimensional electron gas

Spin-singlet and spin-triplet internal transitions of quasi-two-dimensional, negatively charged magneto-excitons (X-) and their evolution with excess electron density have been studied in GaAs/AlGaAs quantum-wells by optically detected resonance (ODR) spectroscopy. In the dilute electron limit, due to magnetic translational invariance, the ODR spectra are dominated by bound-to-continuum bands in contrast to the superficially similar negatively-charged-donor system D-, which exhibits strictly bound-to-bound transitions. With increasing excess electron density in the wells in the magnetic field region corresponding to Landau level filling factors nu < 2 the X- like transitions are blue-shifted; they are absent for nu > 2. The blue-shifted transitions are explained in terms of a new type of collective excitation -- magnetoplasmons bound to a mobile valence band hole, which demonstrates the many-body nature of "exciton-like" magnetoluminescence for nu < 2.

cond-mat↗

arXiv2001

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.

cond-mat↗

arXiv2001

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.

cond-mat.mes-hall↗

arXiv2000

Two-dimensional charged electron-hole complexes in magnetic fields: Keeping magnetic translations preserved

Eigenstates of 2D charged electron-hole complexes in magnetic fields are considered. The operator formalism that allows one to partially separate the center-of-mass motion from internal degrees of freedom is presented. The scheme using magnetic translations is developed for calculating in strong magnetic fields the eigenspectra of negatively charged excitons X^-, a bound state of two electrons and one hole.

cond-mat.mes-hall↗

arXiv1999

Exciton magnetotransport in two-dimensional systems: Weak-localization effects

We consider the effect of a magnetic field $B$ on the transport of neutral composite particles, excitons, in weakly disordered 2D systems. In the case of classical transport, when the interference of different paths is neglected, the magnetic field suppresses exciton transport, and the static diffusion constant $D(B)$ monotonically drops with $B$. When quantum-mechanical corrections due to weak localization are taken into account, $D(B)$ becomes a nonmonotonic function of $B$. In weak magnetic fields, where the magnetic length is much larger than the exciton Bohr radius, $l_B >> a_B$, a positive magnetodiffusion effect is predicted, i.e., the exciton mobility should increase with $B$.

cond-mat.mes-hall↗

arXiv1999

Theory of internal transitions of charged excitons in quantum wells in magnetic fields

For charged semiconductor complexes in magnetic fields B, we discuss an exact classification of states, which is based on magnetic translations. In this scheme, in addition to the total orbital angular momentum projection $M_z$ and electron and hole spins $S_e$, $S_h$, a new exact quantum number appears. This oscillator quantum number, k, is related physically to the center of the cyclotron motion of the complex as a whole. In the dipole approximation k is strictly conserved in magneto-optical transitions. We discuss implications of this new exact selection rule for internal intraband magneto-optical transitions of charged excitons $X^-$ in quantum wells in B.

cond-mat.mes-hall↗