V. E. Bisti

Charged and neutral excitonic complexes in GaAs/AlGaAs quantum wells

The temperature and magnetic-field dependences of the recombination line of multiparticle excitonic complexes in undoped and lightly doped GaAs/AlGaAs quantum wells are investigated. These dependences have previously been attributed to free charged excitons (trions). It is shown that this line corresponds to a bound state of a complex, specifically, to an exciton bound on a neutral donor in a barrier. It is found that as the temperature or pump power is raised, there appear in the recombination spectrum not only a cyclotron replica shifted downward in energy but also a replica which is symmetrically shifted upwards in energy by an amount equal to the cyclotron energy and which is due to emission from an excited state of an impurity complex. The behavior of the cyclotron replicas is studied as a function of the electron density and temperature.

Charge density excitations in bilayer graphene in high magnetic field

AbstractThe charge-density excitations in bilayer graphene at the filling-factor ν 1 at small momenta are considered in the frame of the Hartree-Fock approximation. The presence of small asymmetry of graphene layers is included. The dependence of the magnetoplasmon energy on the bilayer ground state is shown. The energy splitting proportional to

Intersubband collective excitations in quasi-two-dimensional systems in a strong magnetic field

\sqrt H

Interface D− complexes in a two-dimensional electron system

for the symmetric case with half-filled zero-energy levels is found both for bilayer and monolayer graphene.

Structure of the intersubband collective excitations in quasi-two-dimensional systems in a magnetic field

Plasma excitations in a bilayer electron system with weak tunnel coupling have been considered. The effect of the spatial symmetry of the system on the spectrum of plasma excitations has been analyzed. It has been shown experimentally and theoretically that, despite the fundamentally different origins of plasma excitations in systems with different spatial symmetries, their physical properties in the energy range above the tunneling parameter are similar.

Rayleigh scattering of light by two-dimensional electrons in a high magnetic field

The spectrum of intersubband collective excitations of spin and charge density in a system of quasi-two-dimensional electrons is calculated in the strong magnetic field limit for filling factors υ≤4. For υ≤2 two new closely spaced modes of collective excitations are obtained. The modes obtained make it possible to give a new interpretation of the experimentally observed line, which is usually interpreted as being due to single-particle excitations.

Cyclotron spin-flip mode in the extreme quantum limit

Collective intraband charge-density excitations in the quasi-two-dimensional electron system of double GaAs/AlGaAs quantum wells in an external parallel magnetic field B∥ are studied by inelastic light scattering. It has been found that the energy of the excitations under study (acoustic and optical plasmons) exhibits anisotropy depending on the mutual orientation of B∥ and the excitation quasi-momentum k. It is shown theoretically that, in a strong parallel magnetic field, the effects associated with the finite width of the quantum wells dominate over the effects associated with interlayer tunneling and determine the anisotropy of plasmons. The experimental data are compared with a theoretical calculation.

Temperature dependence of luminescence intensity under Bose condensation of interwell excitons

The excitation spectrum of a two-dimensional electron system in high-quality AlGaAs/GaAs quantum wells has been studied by Raman scattering. New Raman lines due to the excitation of interface D− complexes in which two electrons localized in a quantum well are coupled to a charged impurity at the quantum well interface have been identified. The ground state of the interface D− complexes has been found to change in the transverse magnetic field from spin-singlet to spin-triplet, similar to a change in the ground state of the system of two electrons localized in a harmonic potential.