Experimental determination of the mean free path of screened edge magnetoplasmons in a two-dimensional electron gas

Magnetic oscillations of the photovoltage in a two-dimensional electron system with the back gate, exposed to microwave radiation, are studied. The oscillations result from the interference of screened edge magnetoplasmons (EMPs). The mean free path of the EMPs is quantitatively determined by analyzing the dependence of the oscillation amplitude on the electron density. The dependences of the mean free path of the EMPs on the two-dimensional electron density, microwave frequency, electron relaxation time, and the magnetic field are studied. It is found that the dependences agree qualitatively with the known theoretical calculations.     

New type of B-periodic magneto-oscillations in a two-dimensional electron system induced by microwave irradiation

We observe a new type of magneto-oscillations in the photovoltage and the longitudinal resistance of a two-dimensional electron system. The oscillations are induced by microwave radiation and are periodic in magnetic field. The period is determined by the microwave frequency, the electron density, and the distance between potential probes. The phenomenon is accounted for by interference of coherently excited edge magnetoplasmons in the contact regions and offers perspectives for developing new tunable microwave and terahertz detection schemes and spectroscopic techniques.     

Chiral optical Tamm states at the boundary of the medium with helical symmetry of the dielectric tensor

We report the observation of photovoltage oscillations in back-gated two-dimensional electron systems when tuning the density under incident microwaves and in the absence of a magnetic field. The oscillations are periodic in the inverse of the square root of the density. They originate from the interference of screened bulk plasmons with a linear dispersion. This phenomenon can be exploited to devise a spectrometer-on-a-chip for millimeter waves. The influence of a perpendicular magnetic field is investigated and reveals a transformation of screened bulk plasmons waves into screened edge magnetoplasmons.     

Occurrence of a gap in the spectrum of magnetoplasma excitations of a two-dimensional electron disk subjected to a strong in-plane magnetic field

The effect of a parallel magnetic field on the dispersion of bulk and edge magnetoplasmons in a disk-shaped two-dimensional electron system is investigated. It is found that the anisotropy of the electron effective mass that appears in a parallel magnetic field lifts the degeneracy of plasma oscillations in the disk. This is accompanied by the occurrence of a gap in the spectrum of magnetoplasmons, and the magnetic dispersion of these excitations changes from a linear to a parabolic one. The width of the gap is determined by the difference between the frequencies of plasma oscillations along the field and transverse to the field and grows quadratically with the in-plane field strength.     

Observation of plasma and magnetoplasma resonances of two-dimensional electrons in a single MgZnO/ZnO heterojunction

The magnetoluminescence of the two-dimensional electron system in a single Mg _x Zn_{1 ? x} O/ZnO hetero-junction (x = 0.02) at a temperature of 0.3 K in magnetic fields up to 14 T has been studied. The concentration of two-dimensional electrons in the structure under study has been determined from the oscillations of the luminescence intensity as a function of the magnetic field. The value thus obtained is close to the one derived from transport measurements. The resonance corresponding to plasma excitations of two-dimensional electrons has been observed using optical detection of microwave absorption. In a magnetic field, the lower branch of magnetoplasma excitations, which corresponds to the propagation of edge magnetoplasmons in a structure with nearly square geometry, has been observed and investigated.     

Surface magnetoplasmons in a structure with a two- and three-dimensional plasma

Collective oscillations of a two-component structure consisting of a plasma half-space with a two-dimensional plasma layer at its boundary in the presence of a magnetic field have been studied. Possible variants of the spectra of surface magnetoplasmons have been analyzed for three main mutual orientations of the magnetic field, wavevector, and normal to the surface. The case of the field parallel to the boundary where the frequency is an odd function of the wavevector has been discussed in detail.     

Microwave-induced magnetic field oscillations of the electromotive force in a two-dimensional Corbino disk at large filling factors

Microwave-induced magnetic field oscillations of the electromotive force are observed at large filling factors in two-dimensional Corbino disks fabricated on the basis of GaAs/AlAs heterostructures. It is shown that these oscillations of the electromotive force are periodic in the inverse magnetic field and are in antiphase with oscillations of microwave photoconductivity. The experimental data are explained by the inhomogeneous distribution of the microwave field between the coaxial metal contacts to the two-dimensional electron system.     

Magnetoplasmons in gapped graphene in a periodically modulated magnetic field

Motivated by recent experiments on long‐lived magnetoplasmons in the presence of a perpendicular magnetic field, we investigate the dynamical dielectric response function of graphene in contact with a substrate using the random phase approximation. We add a periodically modulated magnetic field within the graphene plane and address both the inter and intra Landau band magnetoplasmons. Verification of the predicted magnetic modulation effects is possible by experiments analogous to those for the zero gap limit.     

Influence of an electric field on the ferromagnetic resonance in a plane-layered magnetic system

The influence of an electric field on the ferromagnetic resonance (FMR) in a multilayer magnetic system consisting of two magnetic layers separated by a thin nonmagnetic interlayer has been investigated. It has been shown that, upon the excitation of magnetization oscillations by a microwave magnetic field, the eigenfrequencies of the ferromagnetic resonance depend on the stationary electric field applied in the plane of the layers. It has also been demonstrated that, in this system, high-frequency magnetization oscillations can be excited by an electric microwave field. The results of the investigation of the polarization properties of the excitation mechanism indicate that this effect can be observed experimentally.     

Microwave-induced magnetic field state with zero conductivity in GaAs/AlAs Corbino disks and hall bars

The microwave photoconductivity of the 2D electron gas in GaAs/AlAs heterostructures has been investigated at a temperature of 4.2 K in magnetic fields up to 1.5 T. It has been found that the magnetic field state with zero conductivity appears in GaAs/AlAs Corbino disks irradiated by 130.70-GHz microwave radiation. This state was previously observed only in GaAs/AlGaAs Corbino disks with much higher electron mobility and lower density. It has been shown that the microwave photoconductivity measured in high magnetic fields on Corbino disks can significantly differ from the value calculated from the results of the measurements on Hall bars. This difference is explained by the fact that the conditions of the appearing magnetoplasmons that affect the magnitude and character of the microwave photoconductivity (photoresistance) in the Corbino disks are nonequivalent to those in the Hall bars.     

Magnetic field effects on the optical response of a film with a rough surface: Voigt geometry

Using the Rayleigh–Fano modal approach we investigate the optical response of a metallic film with a deterministic rough surface taking into account an external magnetic field in the Voigt geometry. For P-polarized light incident onto a deterministic rough surface we calculate the specular and first-order scattered field amplitudes. We also explore the nonreciprocity property and the coupling of the incident light with the surface magnetoplasmons. It is obtained that the magnetic field strength may increase the gap between two minima produced by the splitting of the minima of the zero-field specular reflection. The dispersion relations of the surface magnetoplasmons predict the possible experimental excitation and detection of these modes.     

Optic-phonon-magnetoplasmons at the interface of two polar semiconductors

An interface between two polar semiconductors can support a whole new family of seven type of optic-phonon magnetoplasmons. Six of these arise due to nonequivalence property of propagation introduced by the magnetic field in Voigt configuration and one mainly due to finite plasma density ratio at the interface.     

Modification of Landau Levels in a 2D Ring Due to Rotation Effects and Edge States

The properties of a 2D quantum ring under rotating and external magnetic field effects are investigated. The Landau levels and their inertial effects on them are initially analyzed. Among the results obtained, it is emphasized that the rotation lifted the degeneracy of Landau levels. The second part deals with the electronic confinement in a 2D ring modeled by a hard wall potential. The eigenstates are described by Landau states as long as they are not too close to the ring edges. On the other hand, near the ring edges, the energies increase monotonically. These states are known as edge states. Edge states have a significant role in the physical properties of the ring. Thus, the Fermi energy and magnetization are analyzed. In the specific case of magnetization, two approaches are considered. In the first approach, an analytical result for magnetization is obtained but without considering rotation. Numerical results show the de Haas-Van Alphen (dHvA) oscillations. In the second approach, rotating effects are considered. In addition to the dHvA oscillations, the Aharonov–Bohm-type (AB) oscillations are verified, which are associated with the presence of edge states. The effects of rotation on the results are discussed and it is found that rotation is responsible for inducing AB oscillations.     

Microwave response of a ballistic quantum dot

The microwave response (photovoltage and photoconductance) of a lateral ballistic quantum dot made of a high-mobility two-dimensional electron gas in an AlGaAs/GaAs heterojunction has been studied experimentally in the frequency range of 110–170 GHz. It has been found that the asymmetry of the photovoltage with respect to the sign of the magnetic field has mesoscopic character and depends on both the magnetic field and the microwave power. This indicates the violation of the Onsager reciprocity relations regarding the electron-electron interactions in the mesoscopic photovoltaic effect. A strong increase in the conductance of the quantum dot induced by the microwave radiation and unrelated to heating, as well as the microwave-induced magneto-oscillations, has been discovered.     

Oscillations of the magnetoresistance of a two-dimensional electron gas in a GaAs quantum well with AlAs/GaAs superlattice barriers in a microwave field

The effect of microwave radiation in the frequency range from 1.2 to 10 GHz on the magnetoresistance of a high-mobility two-dimensional electron gas has been studied in a GaAs quantum well with AlAs/GaAs superlattice barriers. It has been found that the microwave field induces oscillations of this magnetoresistance, which are periodic in the reciprocal magnetic field (1/B). It has been shown that the period of these oscillations in the frequency range under study depends on the microwave radiation power.     

Photogalvanic effect in asymmetric lateral superlattice

It is shown that asymmetry of a modulating potential causes appearance of photogalvanic effect in lateral superlattices. The dependence of photovoltage on magnetic field exhibits Weiss-type oscillations.     

Scattering time in GaAs/AlGaAs narrow wires in the presence of magnetic field

Magnetoresistance measurements have been performed in narrow GaAs/AlGaAs wires in order to study the scattering process in mesoscopic wires. Amplitude analysis of the Shubnikov -de Haas oscillations shows that electrons have two scattering times, depending upon the magnetic field range. The critical field which separates these scattering times seems to be determined by the relation between the wire width and the electron cyclotron radius. This effect is discussed in terms of the electron trajectories in a wire under the magnetic field.     

Observation of acoustic edge magnetoplasmons near the filling factor ν = 1

Investigation of acoustic edge magnetoplasma excitations in micrometer two-dimensional electron disks has been carried out. It has been shown that additional acoustic edge magnetoplasma modes associated with the existence of incompressible strips in the two-dimensional electron system caused by Zeeman spin splitting can appear in the system at temperatures below the Zeeman energy. The magnetic dispersion of the first “spin” branch of acoustic edge magnetoplasmons has been studied. It has been shown that this mode vanishes as the filling factor ν = 1 is approached. The dependence of the relative amplitude of acoustic edge magnetoplasmons on the filling factor has also been investigated.     

Study of edge magnetoplasma excitations in two-dimensional electron systems with various edge depletion profiles

Resonant microwave absorption by two-dimensional electrons has been measured using coplanar and strip methods. The influence of the edge of a two-dimensional system on the dispersion of edge magnetoplasmons has been studied. It has been found that the edge width can be varied within wide limits (by almost two orders of magnitude) by changing the etching depth of the crystal. It has been shown that the edge of the electron system in the case of etching through the quantum well has a width of about 0.2 μm, whereas the edge in the case of shallow etching (e.g., down to the donor layer) is smooth and can be as wide as 12 μm. The influence of a logarithmic factor, depending on the edge width of the electron system, on edge magnetoplasma excitations dispersion has been studied.     

Numerical study of chaotic oscillations in the electron beam with virtual cathode in the external non-uniform magnetic fields

In this Letter the results of theoretical investigations of the chaotic microwave oscillator based on the electron beam with a virtual cathode are presented. Nonlinear non-stationary processes in these electron systems are studied by means of numerical analysis of 2.5D model. It was discovered that the non-uniform external magnetic field value controls the dynamical regime of oscillations in the virtual cathode oscillator. The processes of the chaotization of output microwave radiation are described and interpreted from the point of view of the formation and interaction of electron structures (bunches) in the electron beams. The numerical results have shown that the investigated electron system with virtual cathode could be considered as a promising controlled source of wideband chaotic oscillations in the microwave range.