V. E. Kirpichev

Cyclotron spin-flip mode as the lowest-energy excitation of unpolarized integer quantum Hall states

The cyclotron spin-flip modes of spin unpolarized integer quantum Hall states (ν=2,4,6) have been studied with inelastic light scattering. The energy of these modes is significantly smaller compared to the bare cyclotron gap. Second-order exchange corrections are held responsible for a negative energy contribution and render these modes the lowest-energy excitations of unpolarized integer quantum Hall states.

Antiphased Cyclotron-Magnetoplasma Mode in a Quantum Hall System

Max-Planck-Institut fu¨r Festko¨rperforschung,Heisenbergstr. 1, 70569 Stuttgart, Germany(Dated: December 8, 2008)An antiphased magnetoplasma (MP) mode in a two-dimensional electron gas(2DEG) has been studied by means of inelastic light scattering (ILS) spectroscopy.Unlike the cophased MP mode it is purely quantum excitation which has no classicplasma analogue. It is found that zero momentum degeneracy for the antiphasedand cophased modes predicted by the first-order perturbation approach in terms ofthe e-e interaction is lifted. The zero momentum energy gap is determined by anegative correlation shift of the antiphased mode. This shift, observed experimen-tally and calculated theoretically within the second-order perturbation approach, isproportional to the effective Rydberg constant in a semiconductor material.PACS: 71.35.Cc, 71.30.+h, 73.20.Dx

Extra Spin-Wave Mode in Quantum Hall Systems: Beyond the Skyrmion Limit

We report on the observation of a new spin mode in a quantum Hall system in the vicinity of odd electron filling factors under experimental conditions excluding the possibility of Skyrmion excitations. The new mode having presumably zero energy at odd filling factors emerges at small deviations from odd filling factors and couples to the spin exciton. The existence of an extra spin mode assumes a nontrivial magnetic order at partial fillings of Landau levels surrounding quantum Hall ferromagnets other then the Skyrmion crystal.

Dispersion properties of plasma excitations in tunnel-coupled bilayer electron systems

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.

Observation of collective excitations in MgZnO/ZnO two-dimensional electron systems by resonant Raman scattering

The neutral excitations in two-dimensional electron systems (2DES) confined at

Cyclotron spin-flip excitations in a nu = 1/3 quantum Hall ferromagnet.

{\mathrm{Mg}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{O}/\text{ZnO}

Interface D− complexes in a two-dimensional electron system

heterojunctions were studied by a resonant inelastic light scattering (ILS) technique. At zero magnetic field the ILS spectra of intra- and intersubband collective excitations are detected in the wavelength range close to the ZnO direct band gap. The intersubband spectrum is represented by collective modes of charge- and spin-density excitations along with single-particle excitation continuum. The energies of these excitations were characterized on the series of samples and shown to grow sublinearly with the two-dimensional electron density. The intrasubband 2D plasmon was observed at plasma frequency and its square-root momentum dispersion was ascertained. Strong electron-electron correlations are manifested in the energy structure of intersubband excitations. Depolarization and excitonic contributions to the charge- and spin-density excitation energies are extracted in the wide range of 2D-electron densities. The negative excitonic contribution dominates among the many-particle energy terms and results in an unusual hierarchy of 2DES intersubband collective excitation energies.

Hysteresis of giant intensity fluctuations of emission for two-dimensional electrons in the conditions for the integer quantum Hall effect

Inelastic light scattering spectroscopy around the ν =1/3 filling discloses a novel type of cyclotron spin-flip excitation in a quantum Hall system in addition to the excitations previously studied. The excitation energy of the observed mode follows qualitatively the degree of electron spin polarization, reaching a maximum value at ν =1/3 and thus characterizing it as a ν =1/3 ferromagnet eigenmode. Its absolute energy substantially exceeds the theoretical prediction obtained within the renowned single-mode approximation. Double-exciton corrections neglected utilizing the single-mode approach are evaluated within the framework of the excitonic representation and are inferred to be responsible for the observed effect.

Barrier D− complexes in a high-mobility two-dimensional electron system

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.

Fluctuations of the intersubband splitting energy and the potential well shape of two-dimensional electrons in the quantum hall effect regime

On observation of giant intensity fluctuations for the emission of two-dimensional electrons in two-layer electronic systems in the conditions for the integer quantum Hall effect, a hysteresis is detected in the magnetic-field dependences of the amplitude in these fluctuations. It is shown that the hysteresis is observable only at a certain thickness for the barrier separating the electronic layers, and the thickness is such that the inter-layer spacing is comparable with the spacing between electrons in the two-dimensional plane. It is established that the amplitude for the hysteresis in a magnetic field depends on the temperature and on the difference between the concentrations of electrons in the layers. The observed phenomenon can suggest that, in coupled two-layer electronic systems in the conditions for the quantum Hall effect, a new coherent ordered state characterized by two critical temperatures is formed.