Index of content:
Volume 37, Issue 11, November 2011

Strong nonlinear effects in conductivity of thin metallic samples (Review Article)
View Description Hide DescriptionA series of works, dealt with nontrivial nonlinear stationary and nonstationary phenomena accompanying the flow of the transport current through thin pure singlecrystal samples of metals at low temperatures, are discussed. The mechanism of the nonlinearity is magnetidynamical and related with an effect of the intrinsic magnetic field of the current on electron trajectories and, thus, on metal conductivity. The magnetodynamic nonlinearity leads to the nontrivial effect of drop of the resistance in thin samples with increasing the current. At high currents when a radius of curvature of electron trajectories in the intrinsic field of the current becomes smaller than cross sectional dimensions the effect of pinching of the current appears (pinch effect). In this case with increasing the current, the drop of the resistance is replaced by its increase. Experimental investigations of nonlinear currentvoltage characteristics of thin cadmium and tungsten samples are also discussed. In these experiments, not only predictions of the theory are confirmed but new nonlinear effects accompanying the flow of strong currents were found. In particular, generation of selfoscillations of voltage in the regime of a given current was found. With increasing the current, the spectrum of the selfoscillations evolves, following a determined scenario with the transition from discrete to continuous, that indicates the appearance of a chaotic regime.

Nonlinear effects in propagation of radio waves in metals (Review Article)
View Description Hide DescriptionThe main results of works on study of influence of nonlinearity on propagation of radio waves through metals placed in a constant magnetic field are described. The trapping of carriers by the magnetic field of a wave with a large amplitude leads to suppression of collisionless absorption and to a possibility of propagation in metals of waves of various types. In copper, the propagation of helicons becomes possible in the geometry when on the Fermi surface there are open orbits preventing from wave propagation. In zinc, in which the cyclotron absorption by holes exists for any wave lengths in the linear regime, the decrease of this absorption results in a possibility of propagation of an electron doppleron. In noble metals and metals of the Third Group, where any waves are absent in the linear regime, the propagation of nonlinear waves of the new type, which do not have counterparts in the linear regime, becomes possible in the range of weak fields. Multiple reflections of nonlinear waves from internal surfaces of a metallic plate lead to the formation of standing waves in a sample. In this case resonance maxima appear in a dependence of the surface resistance of the sample on a constant magnetic field. In the maxima the transparency coefficient of a metal with respect to radio emission can increase by onetwo orders of magnitude.

Electronic states on the rough surface of a solid
View Description Hide DescriptionSurface electronic states at a periodically rough boundary have been obtained and studied. It is shown that there are two spectral regions of surface states separated by a forbidden band. The properties of the surface states in these regions are quite dissimilar. It is found that the action of surface electronic states gives rise to a subsurface inhomogeneous plasma layer, responsible for the peculiar features of polariton distribution and spatial dispersion of electrostatic vibration frequency. The related dispersion relations are derived. Some peculiarities of electronic state creation are considered for the where the periodic surface roughness is caused by the Rayleigh sound propagation.

Collective excitations of electron gas on the nanotube surface in a magnetic field
View Description Hide DescriptionThe spectra of magnetoplasma waves, zero sound and spin waves in an electron gas on a surface of a nonferromagnetic nanotube in longitudinal magnetic field are considered. The initial spectrum of the electron energy is assumed to be parabolic, and the interelectron interaction is taken into account within the randomphase approximation. It is shown that in a magnetic field there is a shift of the frequency of an intersubband plasmon proportional to a magnetic flux through a crosssection of a tube. The frequency and the damping constant of magnetoplasma waves in a nondegenerate electron gas are calculated. For a great number of filled subbands the frequencies of the zero sound and spin waves in a degenerate electron gas experience oscillations of the type of de Haasvan Alphen and AharonovBohm with changing the density of electrons and magnetic flux.

Microwaveinduced spinflip scattering of electrons in point contacts
View Description Hide DescriptionWe investigate resonant interaction of conduction electrons with an electromagnetic field that irradiates a point contact between a ferromagnetic and a normal metal in the presence of a strong magnetic field of order 1 T. We show that electron spinflips caused by resonant absorption and stimulated emission of photons result in a sharp peak in the magneticfield dependence of the pointcontact resistance. The height of the peak is shown to be directly proportional to the net rate of energy transfer to the electromagnetic field in the point contact due to absorption and stimulated emission of photons. Estimations indicate that our theory can serve as a basis for the explanation of recent experiments [A.M. Kadigrobov et al., New J. Phys. 13, 023007 (2011)].

Rainbow trapping of guided waves
View Description Hide DescriptionWe study theoretically the propagation of a wave packet that is a superposition of three spolarized guided waves with different frequencies in a planar waveguide consisting of a dielectric medium with a graded index of refraction, sandwiched between perfectly conducting walls. The electric field at each point within the waveguide is calculated, and it is shown that each of the constituent modes ceases to propagate at a specific distance along the waveguide that depends on its frequency and on the geometrical and material parameters defining the waveguide. This simple model displays the phenomenon of rainbow trapping of guided waves in an explicit fashion, without the use of a negative index metamaterial.

Electronic density of states for twodimensional system in uniform magnetic and Aharonov–Bohm fields
View Description Hide DescriptionWe study twodimensional electronic gas (2DEG) in the background of the Aharonov–Bohm and constant magnetic fields. The problem of ambiguity of the solutions of the Schrödinger equation is investigated by introducing a finite radius of the flux tube, which then set to zero. Wave functions and spectrum of the 2DEG Hamiltonian are used to construct an expression for the local density of states (LDOS). We obtain that LDOS has a depletion near the origin of the vortex and new peaks, which can’t be explained by using Landau levelstheory.

Fluxcutting and fluxtransport effects in typeII superconductor slabs in a parallel rotating magnetic field
View Description Hide DescriptionThe magnetic response of irreversible typeII superconductor slabs subjected to inplane rotating magnetic field is investigated by applying the circular, elliptic, extendedelliptic, and rectangular fluxlinecutting criticalstate models. Specifically, the models have been applied to explain experiments on a PbBi rotating disk in a fixed magnetic fieldH _{ a }, parallel to the flat surfaces. Here, we have exploited the equivalency of the experimental situation with that of a fixed disk under the action of a parallel magnetic field, rotating in the opposite sense. The effect of both the magnitude H_{a} of the applied magnetic field and its angle of rotation α_{ s } upon the magnetization of the superconductor sample is analyzed. When H_{a} is smaller than the penetration field H_{P} , the magnetization components, parallel and perpendicular to H _{ a }, oscillate with increasing the rotation angle. On the other hand, if the magnitude of the applied field, H_{a} , is larger than H_{P} , both magnetization components become constant functions of α_{ s } at large rotation angles. The evolution of the magnetic induction profiles inside the superconductor is also studied.

Anderson localization in metamaterials with compositional disorder
View Description Hide DescriptionWe consider onedimensional periodiconaverage bilayered models with random perturbations in dielectric constants of both basic slabs composing the structure unitcell. We show that when the thicknesses d_{a} and d_{b} of basic layers are essentially nonequal, d_{a} ≠ d_{b} , the localization length L _{loc} is described by the universal expression for two cases: (a) both layers are made from righthanded materials (the RH–RH model), (b) the a layers are of a righthanded material while the b layers are of a lefthanded material (the RH–LH model). For these models the derived expression for L _{loc} includes all possible correlations between two disorders. However, when d_{a} = d_{b} the RH–LH model exhibits a highly nontrivial properties originated from inhomogeneous distribution of the phase of propagating wave, even in the case of whitenoise disorder. We analytically show that in this case the localization length diverges in the conventional second order in perturbation parameters. Therefore, recently numerically discovered anomalies in L _{loc} are due to the next order of approximation. On the other hand, for the RH–RH model the general expression for L _{loc} remains valid for d_{a} = d_{b} as well.

The Landau band effects in the quantum magnetic oscillations and the deviations from the quasiclassical Lifshitz–Kosevich theory in quasitwodimensional conductors
View Description Hide DescriptionThe quantum magnetic oscillations (QMO) in the layered and quasitwodimensional (2D) conductors deviate from the quasiclassical Lifshitz–Kosevich (LK) theory developed for 3D conventional metals. We discuss deviations related to the broadening of the Landau levels into Landau bands by various mechanisms (layerstacking, magnetic breakdown, incoherence, disorder, localization etc.). Each mechanism yields a specific factor modulating the QMO amplitudes depending on the density of states and electron velocities within the Landau bands. In contrast to the LK theory, these factors differ for the thermodynamic (de Haas–van Alphen (dHvA)) and kinetic (Shubnikov–de Haas (SdH)) oscillations. We calculated the magnetic breakdown damping factors for the SdH and dHvA oscillations in the 2D conductors and analyzed their difference as well as the analogy between the bandwidth and Weiss oscillations. In case of an isotropic 3D metals the kinetic factors become proportional to the thermodynamic ones as is assumed in the LK theory.

Metafluid with anisotropic dynamic mass
View Description Hide DescriptionWe show that a fluid filling the space between metallic cylinders arranged in a twodimensional lattice exhibits anisotropic dynamic mass for sound waves propagating through the lattice, if its unit cell is anisotropic. Using the planewaves expansion method we derive (in the long wavelength limit) a formula for the effective masstensor of the metafluid. The proposed formula is very general—it is valid for arbitrary Bravais lattices and arbitrary filling fractions of the cylinders. We apply our method to a periodic structure with very high anisotropy, when other known methods fail. In particular, we calculate the effective masstensor for sound waves in air with embedded lattice of aluminum cylinders having rectangular cross sections, and obtain excellent agreement with experiment. The proposed method of calculation may find numerous applications for tailoring of metafluids with prescribed anisotropy.