Temperature effects on the magnetoplasmon spectrum of a weakly modulated graphene monolayer

In this work, we determine the effects of temperature on the magnetoplasmon spectrum of an electrically modulated graphene monolayer as well as a two-dimensional electron gas (2DEG). The intra-Landau band magnetoplasmon spectrum within the self-consistent field approach is investigated for both the aforementioned systems. Results obtained not only exhibit Shubnikov-de Haas (SdH) oscillations but also commensurability oscillations (Weiss oscillations). These oscillations are periodic as a function of inverse magnetic field. We find that both the magnetic oscillations, SdH and Weiss, have a greater amplitude and are more robust against temperature in graphene compared to a conventional 2DEG. Furthermore, there is a π phase shift between the magnetoplasmon oscillations in the two systems which can be attributed to Dirac electrons in graphene acquiring a Berry's phase as they traverse a closed path in a magnetic field.     

Influence of a parallel magnetic field on microwave-induced zero-resistance states and magnetoplasmon resonance

In an ultra-clean two-dimensional electron system (2DES), we have observed the magnetoplasmon resonance (MPR) through its microwave-photoconductivity, concurrently with the microwave-induced resistance oscillations (MIRO) and zero-resistance states (ZRS). It is found that the MIRO/ZRS is strongly suppressed by a moderate magnetic field () parallel to the 2DES, while the MPR is robust against a parallel magnetic field. These findings have not been addressed by current models proposed to explain the MIRO/ZRS.     

Observation of retardation effects in the spectrum of two-dimensional plasmons

Retardation effects, theoretically predicted more than 35 years ago, are observed in the spectrum of two-dimensional plasmons in high-electron-mobility GaAs/AlGaAs quantum wells. In zero magnetic field, a strong reduction of the resonant plasma frequency is observed due to the hybridization of the plasma and light modes. In a perpendicular magnetic field B, hybrid cyclotron-plasmon modes appear with a very unusual dependence of the frequency on B field. Experimental results are in excellent agreement with the theory.     

Influence of triplet states on the spectrum of collective spin-polaron excitations in a 2D kondo lattice

The normal and superconducting phases of the ensemble of spin polarons in a two-dimensional Kondo lattice have been considered under the conditions when the hopping integral is comparable to the s-d exchange interaction energy. The polaron excitation spectrum and the superconducting transition temperature have been found taking into account upper triplet states. The change in the concentration dependence of the critical temperature of the transition to the superconducting phase with the relation between the hopping integral and the integral of the s-d exchange coupling has been analyzed.     

Manifestations of incompressible strips in the edge magnetoplasmon spectrum in the quantum Hall effect regime

The behavior of the main edge magnetoplasmon mode in the quantum Hall effect (QHE) regime has been analyzed by the method of optical detection of resonance microwave absorption. Near a filling factor of 2 at a temperature of about 0.3 K, the main edge mode splits into two modes seemingly due to broadening of the incompressible strip at the edge of the two-dimensional electron gas under such conditions.     

Single-particle spectrum of a dilute 2D electron gas

Single-particle spectra of a homogeneous 2D electron gas have been calculated in the microscopic functional approach. The effective mass in this system is found to diverge at r _s ? 7. It is shown that the inclusion of the local exchange and correlation corrections to the effective interaction modifies the instability picture from that obtained in the random phase approximation: in the latter, the instability arises away from the Fermi surface, whereas, with the introduction of the corrections, it manifests itself as the divergence of the effective mass.     

Damping of the magnetoplasmon propagating along a rough dielectric-semiconductor interface

The damping of a surface magnetoplasmon propagating along a rough dielectric-semiconductor interface is considered. The interaction between charge carriers in the semiconductor and the boundary has been taken into account both in the “specularity parameter” and a microscopic model of the boundary. The effective surface relaxation frequency has been analyzed as a function of the boundary parameters and the magnetic field.     

Observation of finite-size effects on a structural phase transition of 2D nanoislands

We study a reversible, temperature-driven structural surface phase transition of Pb/Si(111) nanoislands with a variable-temperature scanning tunneling microscope. Our quantitative measurements indicate that the transition temperature decreases with decreasing island and domain size. The boundaries of the nanoislands also influence the transition. Careful examination of the change in the interior structure of nanoislands near the transition temperature allows us to image the effects of the thermal fluctuations.     

Weak antilocalization in a 2D electron gas with chiral splitting of the spectrum

Motivated by the recent observation of the metal-insulator transition in Si MOSFETs, a study is made of the quantum interference correction to the conductivity in the presence of the Bychkov-Rashba spin splitting. For a small splitting, a crossover from the localizing to antilocalizing regime is obtained. The antilocalization correction vanishes, however, in the limit of a large separation between the chiral branches. The relevance of the chiral splitting for the 2D electron gas in Si MOSFETs is discussed. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 118–123 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Electrode effects on the neutron spectrum of a plasma focus

End-on neutron spectra of a plasma focus were measured by the time-of-flight method. Using an inner electrode with a specially shaped cavity instead of the normal solid or hollow electrodes caused the maximum of the neutron spectrum to shift from 2.66 MeV to 2.85 MeV. It is attempted to explain the effect by the interaction of the electrode, or the impurities emitted by it, with the compressed plasma.     

Influence of phonon dispersion and exciton spectrum on the energy spectrum of magnetopolarons in a quantum well

An analysis is made of the influence of the spatial dispersion of LO phonons and the exciton effect on the energy spectrum of magnetopolarons in a quantum well. It is shown that in optical experiments where light is incident normally on the plane of the quantum well, a discrete spectrum of magnetopolarons is observed. Both the phonon dispersion and the Coulomb attraction of an electron and a hole may lead to a shift of the discrete magnetopolaron energy levels and additional contributions to the broadening of various levels.     

Observation of an interedge magnetoplasmon mode in a degenerate two-dimensional electron gas

We study the propagation of edge magnetoplasmons by time-resolved current measurements in a sample which allows for selective detection of edge states in the quantum Hall regime. At filling factors close to nu=3 we observe two decoupled modes of edge excitations, one of which is related to the innermost compressible strip and is identified as an interedge magnetoplasmon mode. From the analysis of the propagation velocities of each mode the internal spatial parameters of the edge structure are derived.     

Influence of entropy-fluctuation on the Rayleigh spectrum

We discuss the light scattering cross section due to entropy-fluctuation on the region of the central peak of the spectrum. A back-scattering oblique incidence geometry is used in our theoretical calculations which are based on the linear response function approach. Our results show that the power spectrum varies significantly with the incident angle and frequency and so does the light scattering cross section. The results are illustrated with numerical calculations for silicon.Work partially supported by the Brazilian Research Agencies CNPq and FINEP     

Quantum effects on electron-proton bremsstrahlung spectrum in a two-component plasma

The electron-proton low energy bremsstrahlung process is investigated in a two-component plasma. The corrected Kelbg potential taking into account the quantum effects is applied to describe the electron-proton interaction potential in a two-component plasma. The straight-line trajectory method is applied to the motion of the projectile electron in order to investigate the variation of the bremsstrahlung cross-section as a function of the scaled impact parameter, thermal de Broglie wavelength, projectile energy, and photon energy. The results show that the quantum-mechanical effects decrease the bremsstrahlung cross-sections when the de Broglie wavelength (λ) is greater than the Bohr radius (a₀). It is also found that the quantum effects are important only for the region of impact parameters b < 3a ₀. Received 13 March 2001     

Viscoelastic measurements on cross-linked rubbers I. Width and time position of retardation spectrum

Viscoelastic measurements were made on rubber samples cross-linked by sulphur amounts varying from 4% to 20%. The width of the viscoelastic retardation spectrum was decreasing with increasing sulphur amount in the sample. If the dependence on the sulphur content of the spectrum position on time axis is investigated, attention must be given to temperature at which the spectra attained for samples with different sulphur content are correlated. The theoretically predicted shift of the spectra to lower times with increasing cross-link densities may be obtained from experimental results only if the spectra are reduced to the individual characteristic temperatures of the samples, e.g. to the reduced temperaturesT _s .