Transition metamaterials with spatially separated zeros

We report analytical and numerical studies of the effect of the separation distance between zeros of dielectric permittivity and magnetic permeability on the phenomena of resonant absorption and anomalous field enhancement in transition metamaterials. Our studies indicate that these phenomena are robust and strongly polarization-dependent in the presence of the spatial shift between these points. These results are likely to be important for future fundamental and applied studies in the areas of transformation, polarization, and nonlinear optics in metamaterials.     

Calculations of three-dimensional magnetic excitations in permalloy nanostructures with vortex state

Dynamic susceptibility spectra of the vortex state in nanorings and nanodots are studied using three-dimensional micromagnetic simulations. Spatial maps of the susceptibility have enabled identification of various resonance modes. For an exciting field along the x axis, several resonance peaks appear for a thin dot, including a core mode, whereas only one main resonance peak is detected for a ring corresponding to a volume mode with uniform magnetization perpendicular to the exciting field (x direction). A low-frequency resonance peak related to a surface mode and a high-frequency resonance peak viewed as an edge mode are additionally observed for a thick ring. These three resonance modes (surface, volume and edge modes) which correspond to low, intermediate and high-frequency resonance peaks, respectively, are also captured for an exciting field along the y axis. In addition, a mixed edge and volume mode is revealed at a higher frequency.     

Current-driven vortex oscillations in metallic nanocontacts

We present experimental evidence of subgigahertz spin-transfer oscillations in metallic nanocontacts that are due to the translational motion of a magnetic vortex. The vortex is shown to execute large-amplitude orbital motion outside the contact region. Good agreement with analytical theory and micromagnetics simulations is found.     

Azimuthons: spatially modulated vortex solitons

We introduce a novel class of spatially localized self-trapped ringlike singular optical beams in nonlinear media, the so-called azimuthons, which appear due to a continuous azimuthal deformation of vortex solitons. We demonstrate that the azimuthons are characterized by two independent integer indices, the topological charge m and the number N of the intensity peaks along the ring. Each soliton family includes azimuthons with negative, positive, and zero angular velocity.     

Spin-wave eigenmodes of permalloy squares with a closure domain structure

Quantized spin-wave eigenmodes in single, 16 nm thick and 0.75 to 4 mum wide square permalloy islands with a fourfold closure domain structure have been investigated by microfocus Brillouin light scattering spectroscopy and time resolved scanning magneto-optical Kerr microscopy. Up to six eigenmodes were detected and classified. The main direction of the spin-wave quantization in the domains was found to be perpendicular to the local static magnetization. An additional less pronounced quantization along the direction parallel to the static magnetization was also observed.     

Ultrasound and vortex oscillations in high-temperature superconductors

An HTSC powder sample with grain (particle) diameter of 20–50 μm placed in a dc magnetic field B ₀ and cooled to a temperature below the superconducting transition temperature was exposed to the radiofrequency (rf) pulsed magnetic field B _∼ (B _∼ ⊥ B ₀) at a carrier frequency of 30.7 MHz. Stable echo signals were recorded which followed different rf-pulse trains. This phenomenon has the following mechanism. The rf magnetic field stimulates fluxoid oscillations on the HTSC grain surface, which are transformed into lattice oscillations through the pinning centers and induce a propagating sound wave. The second-order nonlinearity with respect to the gradient of the crystal lattice deviation from the equilibrium position taken into account in the sound wave equation yields the dependence of the crystal lattice natural frequency on the amplitude and length of the pulses which excite these oscillations. This dependence is responsible for the emergence of echo signals.     

Larmor precession in polarization spectroscopy with spatially separated beams

Sodium vapour in a sealed cell is irradiated by two counter-propagating but laterally displaced beams from the same laser, tuned to one of the hf components of the D₁ line. Atoms pumped by the stronger beam, circularly polarized, precess in a transverse magnetic field, < 300 mG, during their passage to the weaker beam where their orientation is monitored. The observed signals are interpreted quantitatively.     

Superconductivity at dielectric pairing of spatially separated quasiparticles

A new mechanism of the superconductivity based upon the pairing of the spatially separated electrons and holes due to their Coulomb attraction is presented. In the systems considered the phase of the order parameter is not fixed and therefore the charges superfluid flow connected with non-dissipative electrical currents is possible. The critical temperature T_c may be high (? 100°K). The critical current has been found. The diamagnetic response and the coefficient of the electromagnetic wave absorption in the systems have been calculated. The possible experiments are discussed.     

The property lattice of spatially separated quantum systems

We consider a quantum system composed of two subsystems. Among the properties of this system we study the set of those that can be tested when the subsystems are spatially separated. We show that not all properties satisfy this criterion, but that there are enough such properties to characterize any pure state of the composed system.     

Instability of spatially separated plasma beams. III

Two-stream instability in spatially separated plasma beams having a finite thickness are investigated in the quasihydrodynamic approximation. It is shown that in beams having a finite thickness the instability domain is bounded for both low and high drift velocities. The minimum drift velocity at which instability develops may be less than the corresponding magnitude in semibounded beams. With decreasing thickness of the layers, the maximum growth rate of the amplified waves falls off. An influence of a dielectric interlayer between beams on the character of the instability is revealed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 4, pp. 521–527, April, 1972.     

Electron beam excitation of nonequilibrium effects in spatially separated superconductors

A superconductor driven into a nonequilibrium state under electron beam irradiation emits phonons. They can be detected by a spatially separated superconductor of the same material. This phenomenon, which is typical only to be superconducting state, is used to map a superconductor in a scanning electron microscope.     

Entanglement of two spatially separated qubits via correlated photons

We show that a high degree of steady-state entanglement between two spatially separated and initially uncoupled qubits can be achieved via interaction with a quantized squeezed field in a cavity. The cavity field induces two-photon coherence, which is crucial in creating entanglement between the qubits. Optimum entanglement is obtained when the less dissipative qubit is incoherently pumped while the other dissipates the excitation. Given the current state-of-the-art in cavity quantum electrodynamics and squeezed light sources, our scheme presents an effective way for light-to-matter entanglement transfer.     

Optical weak link between two spatially separated Bose-Einstein condensates

Two spatially separate Bose-Einstein condensates were prepared in an optical double-well potential. A bidirectional coupling between the two condensates was established by two pairs of Bragg beams which continuously outcoupled atoms in opposite directions. The atomic currents induced by the optical coupling depend on the relative phase of the two condensates and on an additional controllable coupling phase. This was observed through symmetric and antisymmetric correlations between the two outcoupled atom fluxes. A Josephson optical coupling of two condensates in a ring geometry is proposed. The continuous outcoupling method was used to monitor slow relative motions of two elongated condensates and characterize the trapping potential.     

MFM study of magnetic vortex cores in circular permalloy dots: behavior in external field

In a circular dot of permalloy with an appropriate size, a vortex structure with perpendicular (turned-up) magnetization at the core is realized. The existence of the perpendicular magnetization spot has been confirmed and the direction of the magnetization, up or down, has been determined by magnetic force microscopy (MFM) for permalloy dots with the diameter of 0.1–1 μm. The switching field of turned-up magnetization is determined by applying external fields perpendicularly and in tilted directions to the plane. By comparing the MFM results and the magnetization curves measured by a SQUID magnetometer, the switching process of turned-up magnetization is argued.     

Phase transitions in a system of spatially separated electrons and holes

The formation of a superfluid exciton liquid in a system of spatially separated electrons and holes in a system of two coupled quantum wells is predicted and its properties are investigated. The ground-state energy and the equilibrium density of the exciton liquid are calculated as functions of distance D between the quantum wells. The properties of a rarefied exciton gas with dipole-dipole repulsions are considered, where this gas is the metastable phase for D<1.9a* and the stable phase for D<1.9a* (a* is the radius of the two-dimensional exciton). The gas-liquid quantum transition is examined for increasing D. The Berezinskii-Kosterlitz-Thouless transition temperatures, at which superfluidity arises in the system, are found for different values of D. Possible experimental manifestations of the predicted effects are discussed. Zh. éksp. Teor. Fiz. 111, 1879–1895 (May 1997)