Hydrodynamic theory of plasma oscillations in quasi-two-dimensional systems

We show that a hydrodynamic theory can be applied to calculate the dispersion relation of plasma oscillations in a quasi-two-dimensional system. It also leads to the conclusion that additional “multipole” modes may exist in the system.     

Parallel magnetic field induced giant magnetoresistance in low density quasi-two-dimensional layers

We provide a possible theoretical explanation for the recently observed giant positive magnetoresistance in high mobility low density quasi-two-dimensional electron and hole systems. Our explanation is based on the strong coupling of the parallel field to the orbital motion arising from the finite layer thickness and the large Fermi wavelength of the quasi-two-dimensional system at low carrier densities.     

Magnetic scattering effects on magnetoresistance in a quasi-two-dimensional disordered electron system

Magnetic-impurity-scattering effects in a quasi-2D disordered electron system have been investigated theoretically with the diagrammatic techniques in perturbation theory. The analytical expressions for magnetoconductivities due to weak-localization effects have been obtained as functions of elastic, inelastic and magnetic scattering times. The relevant dimensional crossover behavior from 3D to 2D with decreasing the interlayer coupling has been discussed, and the condition for the crossover has been obtained. Received 20 March 2001 and Received in final form 28 June 2001     

Tunnel magnetoresistance oscillations in a ferromagnet-insulator-ferromagnet system

A model of spin-dependent transport of electrons through a ferromagnet-insulator-ferromagnet structure is developed. It takes into account the image forces, tunnel barrier parameters, and effective masses of an electron tunneling in the barrier and in the ferromagnetic electrode in the free electron approximation. Calculations for an iron-aluminum oxide-iron structure show that, with an increase in the bias voltage, the tunnel magnetoresistance decreases monotonically and then breaks into damped oscillations caused by the interference of the electrons’ wave functions in the conduction region of the potential barrier. The image forces increase the tunnel magnetoresistance by two or three times.     

Specific features of quantum oscillations of magnetization in quasi-two-dimensional antiferromagnetic semimetals

The specific features of quantum oscillations of the magnetization in quasi-two-dimensional wide-band-gap antiferromagnetic semimetals with a low concentration of charge carriers have been considered theoretically. It has been shown that, in these systems, the Fermi energy determined from the analysis of the frequency of the de Haas–van Alphen oscillations according to the standard procedure can differ significantly from the true value. For the correct determination of the Fermi energy in the canted phase, it has been proposed to analyze quantum oscillations of the magnetization M not as a function of the inverse magnetic field 1/H, but as a function of 1/cosγ, where the angle γ characterizes the inclination angle of the magnetic field with respect to the plane of the quasi-two-dimensional semimetal.     

Effects of intersubband coupling on Friedel oscillations in quasi-two-dimensional electron systems

We have studied the effect of screening on an ionized impurity and Freidel oscillations in a quasi-two-dimensional (Q2D) electron system in which multisubbands are occupied. The screening effects of the Q2D electron gas are investigated within the random-phase approximation. We show that in a quantum well in which two subbands are occupied, the intersubband coupling significantly deepens the first minimum in the Friedel oscillation.     

Weber blockade theory of magnetoresistance oscillations in superconducting strips

Recent experiments on the conductance of thin, narrow superconducting strips have found periodic fluctuations, as a function of the perpendicular magnetic field, with a period corresponding to approximately two flux quanta per strip area [A. Johansson et al., Phys. Rev. Lett. 95, 116805 (2005)]. We argue that the low-energy degrees of freedom responsible for dissipation correspond to vortex motion. Using vortex-charge duality, we show that the superconducting strip behaves as the dual of a quantum dot, with the vortices, magnetic field, and bias current respectively playing the roles of the electrons, gate voltage, and source-drain voltage. In the bias-current versus magnetic-field plane, the strip conductance displays regions of small vortex conductance (i.e., small electrical resistance) that we term "Weber blockade" diamonds, which are dual to Coulomb blockade diamonds in quantum dots.     

Plasma oscillations in spheres and the magnetoresistance of potassium

We have observed in potassium the spectrum of the longitudinal helicon oscillations. We have used these oscillations to measure the magnetoresistance and Hall coefficient. In addition, a low frequency method for the measurement of magnetoresistance in metals is demonstrated with experiments on single crystal potassium spheres. The magnetoresistance saturates, but its magnitude depends upon sample history.     

Angular magnetoresistance oscillations in bilayers in tilted magnetic fields

Angular magnetoresistance oscillations (AMRO) were originally discovered in organic conductors and then found in many other layered metals. It should be possible to observe AMRO to semiconducting bilayers as well. Here we present an intuitive geometrical interpretation of AMRO as the Aharonov–Bohm interference effect, both in real and momentum spaces, for balanced and imbalanced bilayers. Applications to the experiments with bilayers in tilted magnetic fields in the metallic state are discussed. We speculate that AMRO may be also observed when each layer of the bilayer is in the composite-fermion state.     

Surface acoustic-wave-induced magnetoresistance oscillations in a two-dimensional electron gas

We study the geometrical commensurability oscillations imposed on the resistivity of 2D electrons in a perpendicular magnetic field by a propagating surface acoustic wave (SAW). We show that, for omega相似文献   

Radiation-induced magnetoresistance oscillations in a 2D electron gas

Recent measurements of a 2D electron gas subjected to microwave radiation reveal a magnetoresistance with an oscillatory dependence on the ratio of radiation frequency to cyclotron frequency. We perform a diagrammatic calculation and find radiation-induced resistivity oscillations with the correct period and phase. Results are explained via a simple picture of current induced by photoexcited disorder-scattered electrons. The oscillations increase with radiation intensity, easily exceeding the dark resistivity and resulting in negative-resistivity minima. At high intensity, we identify additional features, likely due to multiphoton processes, which have yet to be observed experimentally.     

Giant magnetoresistance oscillations caused by cyclotron resonance harmonics

For high-mobility two-dimensional electrons at a GaAs/AlGaAs heterojunction, we have studied, both experimentally and theoretically, the recently discovered giant magnetoresistance oscillations with nearly zero resistance in the oscillation minima which appear under microwave radiation. We have proposed a model based on nonequilibrium occupation of Landau levels caused by radiation which describes the oscillation picture.     

Intermodulation of transverse magnetoresistance oscillations in structures with strong intersubband interaction

In the Shubnikov–de Haas oscillation spectrum of doped InAs/AlSb structures, high-amplitude peaks are established at combination frequencies. It is demonstrated that they are caused by a significant contribution of intersubband scattering to the processes of electron-electron interaction. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 32–38, December, 2008.     

Effect of disorder on magnetoresistance oscillations in nanoperforated superconducting TiN films

The low-temperature transport properties of nanoperforated superconducting TiN films have been experimentally studied. A periodic dependence of the resistance on an external magnetic field, with a period corresponding to a magnetic flux quantum per cell, is observed. An anomalous temperature dependence of the oscillation amplitude is found. The role of the effects of electron-electron interaction and localization in the physical properties of arrays of weak links, based on strongly disordered superconducting films, is discussed.