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By measuring magnetoresistance and Hall effect in classically moderate perpendicular magnetic field in Si-MOSFET-type macroscopic antidot array we found a novel effect: nonlinear with field, temperature- and density-dependent Hall resistivity. We discuss qualitative explanation of the phenomenon and suggest that it might originate from strong temperature dependence of the resistivity and mobility in the shells of the antidots., 4 pages, 7 figures

The effects of gate voltage V g on the Landau levels (LLs) of the AA-stacked bilayer graphene are investigated by the Peierls tight-binding model. A uniform perpendicular magnetic field ( B 0 ) produces two groups of LLs. V g can raise the threshold LL energies, increase the quantum numbers of the LLs nearest to the chemical potential, and modify the LL spacing. An energy gap is induced by B 0 , and it has an oscillatory dependence on V g and B 0 . There exist semiconductor-semimetal transitions at certain critical gate voltages. Some carriers are transferred between similar sublattices on the two different layers. On the other hand, the main features of the Landau wave functions remain unchanged.

We determine the critical current density of the superconductor having an array of hole exposed under electric current and under a perpendicular magnetic field. It is assumed that the inner holes sides are accounted in the de Gennes boundary condition while outer edge is in contact with vacuum. The critical current calculation was done after solving time dependent Ginzburg-Landau equation and evaluating the electric voltage. The enhancement factor of the critical currents due to the boundary condition is discussed.

The Kekulé structure count (K) for some types of polycyclic aromatic hydrocarbons (PAHs), such as fluoranthene and perylene, can be factorized into the product of those for two or more aromatic subunits. The ring-current map for these PAHs placed in a perpendicular magnetic field exhibits a substantial localization on aromatic subunits. We found that such localization of π circulation is a characteristic of fairly small K-factorizable species in the neutral electronic state. Even in such a case, no single π molecular orbital (πMO) is associated with localized π circulation. Apparent localization of π circulation is caused by the superposition of currents induced by all occupied πMOs. π circulation is less localized in larger K-factorizable species.

AC losses in a superconductor strip are numerically evaluated by means of a finite element method formulated with a current vector potential. The expressions of AC losses in an infinite slab that corresponds to a simple model of infinitely stacked strips are also derived theoretically. It is assumed that the voltage-current characteristics of the superconductors are represented by Bean’s critical state model. The typical operation pattern of a Superconducting Magnetic Energy Storage (SMES) coil with direct and alternating transport currents in an external AC magnetic field is taken into account as the electromagnetic environment for both the single strip and the infinite slab. By using the obtained results of AC losses, the influences of the transport currents on the total losses are discussed quantitatively.

For AC applications of high-temperature superconductors, such as REBa2Cu3O y (REBCO, RE = rare earth) superconducting tapes, an AC loss is a great part of total heat load of cooling systems. In the case of conduction cooling, it may cause a serious temperature rise of the superconducting systems. Therefore, it is very important to reduce the AC loss in superconducting windings and grasp its properties under various conditions. For AC loss reduction, REBCO tapes should be scribed into a multifilamentary structure by the laser-scribing technique. In this study, AC loss properties in the non-scribed and scribed tapes were investigated, especially for B m < B p, where B p is the breaking point of the AC loss curve and corresponds to the penetration field where the magnetic flux penetrates to the center of the tape or filaments. Further, the dependences of B p on the number of stacking tapes and filaments were investigated from the viewpoint of demagnetization effect. It was cleared that the AC loss for B m < B p decrease and B p increase with increasing number of stacked tapes.

We propose a new scheme to achieve an effective spin/valley filter in silicene with extended line defect on the basis of spin–valley coupling due to the intrinsic spin-orbit coupling (SOC). The transmission coefficient of the spin/valley states is seriously affected by the SOC. When a perpendicular magnetic field is applied on one side of the line defect, one valley state will experience backscattering, but the other valley will not; this leads to high valley polarization in all transmission directions. Moreover, the spin/valley polarization can be enhanced to 96% with the aid of a perpendicular electric field.

We study the spectrum of an electron gas subjected to a two-dimensional non-Bravais lattice potential and a perpendicular magnetic field simultaneously. We derive the difference equations, which are not periodic in the x direction for any value of the gauge potential in Landau gauge ( 0 , Hx , 0 ) . The spectrum has a fractal structure and is incommensurate along the magnitude of the magnetic field.

We study optically-induced collective excitations of graphene in the presence of a strong perpendicular magnetic field and a single impurity. We determine the energies and absorption strengths of these excitations, which become localised on the impurity. Two different types of impurity are considered i. the long-range Coulomb impurity, ii. a delta-function impurity located at either an A or B graphene sublattice site. Both impurity types result in some bound states appearing both above and below the magnetoplasmon continuum, although the effect of the short-range impurity is less pronounced. The dependence of the energies and oscillator strengths of the bound states on the filling factor is investigated., Comment: 4 pages, 4 figures, accepted for publication in Ann. Phys. (Leipzig)

The magnetization of heavy holes in III-V semiconductor quantum wells with Rashba spin-orbit coupling (SOC) in an external perpendicular magnetic field is theoretically studied. We concentrate on the effects on the magnetization induced by the system boundary, the Rashba SOC and the temperature. It is found that the sawtooth-like de Haas--van Alphen (dHvA) oscillations of the magnetization will change dramatically in the presence of such three factors. Especially, the effects of the edge states and Rashba SOC on the magnetization are more evident when the magnetic field is more small. The oscillation center will shift when the boundary effect is considered and the Rashba SOC will bring beating patterns to the dHvA oscillations. These effects on the dHvA oscillations are preferred to be observed at low temperature. With increasing the temperature, the dHvA oscillations turn to be blurred and eventually disappear., Comment: 6 pages, 6 figures

The behavior of a magnetic fluid drops in a thin film under the action of a perpendicular magnetic field is investigated. Instability of the form of a drop and formation of star-like patterns in the spot of contact of the deformed drop with layer boundaries is detected. The disintegration of a drop attended fractal pattern formation is investigated. Dependence of character of these processes on a size of drops, concentration and rate of a magnetic field rise is determined.

Properties of disordered thin films are discussed based on the viewpoint that superconducting islands are formed in the system. These lead to superconducting correlations confined in space, which are known to form spontaneously in thin films. Application of a perpendicular magnetic field can drive the system from the superconducting state (characterized by phase-rigidity between the sample edges) to an insulating state in which there are no phase-correlations between the edges of the system. On the insulating side the existence of superconducting islands leads to a non-monotonic magnetoresistance. Several other features seen in experiment are explained., Contribution to the proceedings of "Fluctuations and phase transitions in superconductors", Nazareth Ilit, Israel, June 10-14, 2007

© 2016 American Physical Society.We report a study on the complete spin-wave spectrum inside a vortex-state nanodisk. Transformation of this spectrum is continuously monitored as the nanodisk becomes gradually magnetized by a perpendicular magnetic field and encounters a second-order phase transition to the uniformly magnetized state. This reveals the bijective relationship that exists between the eigenmodes in the vortex state and the ones in the saturated state. It is found that the gyrotropic mode can be continuously viewed as a uniform phase precession, which uniquely softens (its frequency vanishes) at the saturation field to transform above into the Kittel mode. By contrast, the other spin-wave modes remain finite as a function of the applied field, while their character is altered by level anticrossing.

The quantum Hall effect arises from the quantum behavior of two-dimensional, strongly-interacting electrons exposed to a strong, perpendicular magnetic field [1, 2]. Conventionally treated from a many-body perspective, we instead treat the system from the few-body perspective using collective coordinates and the hyperspherical adiabatic technique developed originally for atomic systems [3]. The grand angular momentum K from K -harmonic few-body theory, is shown to be an approximate good collective quantum number in this system, and is shown to correlate with known fractional quantum Hall (FQH) states at experimentally observed filling factors.

Interacting bilayers placed in perpendicular magnetic field exhibit a peculiar quantum Hall state (QHS) at total filling factor ν = 1 , owing to the carrier–carrier interaction in the two layers. The physics of the ν = 1 QHS is similar to that of the many-particle ground state of a superconductor. Unlike conventional superconductors, however, in the ν = 1 QHS carriers in one layer pair with vacancies in the opposite layer forming charge neutral particles which flow without dissipation at the lowest temperatures. Here we review the experimental evidence supporting this picture, with an emphasis on magnetotransport in interacting GaAs hole bilayers in a configuration where equal and opposite currents are passed in the two layers.

We simulate the electron transport in the inversion layer of ultra-thin silicon-on-insulator devices in the presence of a perpendicular magnetic field. We compute and compare the Hall mobility, the magnetoresistance mobility and the low-field drift mobility. The Hall and magnetoresistance factors, which are essential in order to have precise information on the effective mobility from experimental Hall or magnetoresistance data, are computed for various ultrathin SOI structures and temperatures. The results show that Hall mobility and magnetoresistance mobility are modulated by the SOI size effects, in particular the subband splitting. Not only the Hall and magnetoresistance factors can be quite different from unity, but they also depend on the device geometry and operating conditions.

The magnetic translation group describes the symmetry of the itinerant electron on two-dimensional lattice with perpendicular magnetic field. For such a finite system, with periodic condition the properties of the irreducible representations of this group are responsible for the tight-binding analogue of cyclotron orbits of the free electron case. The relation between the size of the planar lattice and the structure of the group and its irreducible representations is pointed out.

We experimentally investigate the transport through a shunted surface superlattice under the influence of a magnetic field applied perpendicular to the current direction. The current–voltage characteristics of these surface superlattices exhibit a peak which is followed by a wide region of negative differential resistance. The application of a transverse magnetic field has a profound influence on the position and height of this peak. The recorded shifts are compared to the predictions of different superlattice transport theories. Since these theories predict a different dependence on the magnetic field strength, the transport mechanism in the surface superlattice structures can be uniquely determined.

In this paper, a CMOS magnetic sensor integrated circuit (IC) for a perpendicular magnetic field is introduced. The sensor integrated circuit is designed and fabricated in a 0.6 μm digital CMOS process. It consists of a pair of common-source split-drain magnetic field-effect transistor (MAGFET), a pre-processing circuit with a switches array, a correlated double sampling (CDS) circuit and a digital controlling part. The measurements of perpendicular magnetic field as well as the noise shaping are realized on-chip by the two functioning modes of the sensor integrated circuit. The MAGFET is sectorial with a radius of 48 μm and an angle of 90°, and the measured sensitivity S A (current-related sensitivity) is 3.61%/T. At the working frequency of 10 kHz, the sensitivity of the magnetic sensor is 2.62 V/T.

Methods to mitigate a perpendicular magnetic field component on the surface of a high temperature superconducting (HTS) tape in HTS coils by arranging low current density (LCD) coils in the edges were studied analytically. Four types of winding arrangement with and without the LCD coils at both edges of the superconducting winding, which are used to model a three-phase 40 MVA HTS transformer, were proposed. The results of magnetic field analysis in the proposed winding arrangements reveal that (1) the maximum perpendicular magnetic field (B/sub /spl perp/max/) on the surface of the HTS tape is influenced markedly by the LCD coils arrangements and that (2) the winding arrangement which is LCD coils installed in both edges of top and bottom in the LV and the HV winding is very effective in reducing the B/sub /spl perp/max/ in both edges of top and bottom.

The tight-binding model is employed to study magnetoelectronic structures of the AB-stacked graphite. A specifically full band calculation on overall energy region is presented to compare with SWMcC method, which only concerns the magnetoelectronic structures along the HKH-axis. It is found that magnetoband structures, strongly depending on the perpendicular magnetic field (B) and the interlayer interactions, exhibit 0D, 1D and 2D characteristics at the strong magnetic field. The physical origin of 0D, 1D and 2D Landau levels is intensely discussed to show its speciality for graphite. Pronounced structures, including sharp peaks, square-root peaks, and logarithmic divergences, can be clearly found in the density of states (DOS). And the energy dispersions and DOS are specially sensitive to the magnitude of B: the lower the magnetic field is, the more Landau levels exist nearby Fermi energy (EF). Meanwhile, the interlayer interactions significantly affect the state energies and the DOS features, e.g., peak position and peak shape. DOS in the form of sharp peak (square-root peaks) below (above) EF is expected to play an important role in such physical properties as absorption spectra. � 2005 Elsevier Ltd. All rights reserved.

The electron motion in a strong perpendicular magnetic field close to the impenetrable obstacle is considered by the semi-classical and quantum points of view. We investigated an influence of a shape of the forbidden region to the formation of the plateaux in the one electron energy spectrum and transmissions between dot and antidot states. In the semi-classical regime electrons can be treated as charged particles with well-defined trajectories pinned to the potential wall. This approach, combined with singular equation technique in quantum calculations, has given us a possibility to investigate stripe-shaped and bow-shaped antidots with sharp edges and to find a way for controlled manipulation of the parameters of systems with an effort to get desired physical properties.

Low-temperature magnetotransport measurements were performed on an Al0.25Ga0.75N∕GaN two-dimensional electron system. In this system, we observe Shubnikov-de Haas (SdH) oscillations in a perpendicular magnetic field B. By measuring the positions of a pair of spin-split SdH maxima, we are able to estimate the g‐factors at different Landau level (LL) indices. We find the g‐factor is enhanced over its bulk value in GaN (≅2) due to many-body exchange interactions. Moreover, the measured g‐factor increases with decreasing LL index, indicating that many-body electron–electron interactions become stronger as the number of occupied LLs decreases. Our results suggest that the exchange energy Eex shows an approximately linear B dependence.

The spectrum of two-dimensional 2D electrons subjected to a weak 2D potential and a perpendicular magnetic field is composed of Landau bands with a fractal internal pattern of subbands and minigaps referred to as Hofstadter's butterfly. The Hall conductance may serve as a spectroscopic tool as each filled sub-band contributes a specific quantized value. Advances in sample fabrication now finally offer access to the regime away from the limiting case of a very weak potential. Complex behavior of the Hall conductance is observed and assigned to Landau band coupling induced rearrangements within the butterfly.

The quantized electron-diffusion thermoelectric power S is studied for a general one-dimensional band structure in ballistic channels with applications to a single-quantum-well channel and tunnel-coupled double-quantum-well channels in a perpendicular magnetic field. We find a field-induced sign reversal of S and oscillations in double-well channels.

Three YBCO thin films on sapphire substrate with widths of 3, 5, and 10 mm were prepared, and their AC loss characteristics were studied experimentally. The total AC loss dissipated in samples carrying AC transport current in an AC transverse magnetic field was measured by an electromagnetic method. The total AC loss in YBCO film is proportional to the film width and the perpendicular magnetic field component, a component of the transverse magnetic field that is perpendicular to the film wide face. Reduction of the film width and/or the perpendicular magnetic field component is an essential means of decreasing the total AC loss. When plotting the total AC loss divided by film width against the perpendicular magnetic field component, curves for various film widths and field angles almost agree with each other. The total AC loss can be estimated by analytical expressions except in an intermediate range of the perpendicular magnetic field component. The experimental results indicate two engineering approaches for reducing the total AC loss in YBCO film: decreasing the film width and decreasing the perpendicular magnetic field component. Findings have shown empirically that decreasing the film width and decreasing sinα, where α is the field angle, are equivalently effective in reducing the total AC loss.

Magnetoelectronic structures of a two-dimensional (2D) graphite sheet are calculated by the tight-binding model. They are very sensitive to the magnitude of perpendicular magnetic field (B). B imposes the periodical boundary condition on the Bloch functions in the real and momentum spaces. Thus, B changes energy dispersions, energy spacing, bandwidth, and oscillation period of Landau levels. B could reduce the dimensionality of a graphite sheet. Energy dispersions mainly exhibit zero-dimensional (or 1D) characteristics. A lot of delta-function-like peaks (or square-root peaks) in the density of states can be clearly found. The magnetic field dramatically changes the joint density of states and the magnetoabsorption spectra. So, many peaks with different structures are produced.

The scaling of current–voltage relations of Bi-based (BSCCO) superconducting thin films subjected to a perpendicular magnetic field is investigated theoretically using the flux-creep model in which distributed washboard pinning potential is considered and flux-flow is taken into account. The pinning parameters of the films are estimated by fitting the calculated E–J curves to experimental ones. Moreover, the theory gives a possibility to explain power-law behaviour (E–Jn) in type-II superconductors.

A comparison between two different approaches for the solution of the Schrodinger equation in a mesoscopic device in a perpendicular magnetic field is presented. Relative advantages of the two methods are discussed, with reference to model calculations and to the case of a spatially varying magnetic field.

In the paper we present experimental results of power losses measurements in a YBCO-123 coated conductor carrying a DC (or AC) transport current when subjected simultaneously to an external AC magnetic field. Two kinds of measurements were carried out; the first was AC transport current losses as a function of the current amplitude and the AC external magnetic field (“AC–AC” case); the second was dynamic resistance losses versus DC transport current and the AC external magnetic field (“DC–AC” case). Additionally, for both cases the magnetization losses were measured. The increase of the AC transport current loss due to the AC external magnetic field in the full saturation regime is described well with the dynamic resistance effect. This makes it possible to replace the AC transport current measurement in AC applied magnetic field with the much more simple dynamic resistance loss measurement when the total AC loss has to be determined.

We have grown single crystals of WTe2 by a self-flux method and evaluated the quality of the crystals. A Hall bar-type device was fabricated from an as-exfoliated film on a Si substrate and longitudinal resistance Rxx was measured. Rxx increased with an applied perpendicular magnetic field without saturation and an extremely large magnetoresistance as high as 376,059 % was observed at 8.27 T and 1.7 K.

The electronic structure of InAs/AlSb/GaSb quantum wells embedded in AlSb barriers and in the presence of a perpendicular magnetic field is studied theoretically within the $14$-band ${\bf k}\cdot{\bf p}$ approach without making the axial approximation. At zero magnetic field, for a quantum well with a wide InAs layer and a wide GaSb layer, the energy of an electron-like subband can be lower than the energy of hole-like subbands. As the strength of the magnetic field increases, the Landau levels of this electron-like subband grow in energy and intersect the Landau levels of the hole-like subbands. The electron-hole hybridization leads to a series of anti-crossing splittings of the Landau levels. The energies of some Landau level transitions and their corresponding transition strengthes are calculated. The magnetic field dependence of some dominant transitions is shown with their corresponding initial-states and final-states indicated. This information should be useful in analyzing an experimentally measured magneto-optical spectrum. At high magnetic fields, multiple transitions due to the initial-state splitting can be observed. The dominant transitions at high fields can be roughly viewed as two spin-split Landau level transitions with many electron-hole hybridization induced splittings. The energy separations between the dominant transitions may decrease or increase versus the magnetic field locally, or may be almost field independent. The separations can be tuned by changing the width of InAs layer or the width of middle AlSb layer. When the magnetic field is tilted, the electron-like Landau level transitions show additional anti-crossing splittings due to the subband-Landau level coupling.

The spin polarization of the FQHE ground states at fixed filling factors is analyzed within a composite fermion model. As a function of the perpendicular magnetic field several cross-overs between differently polarized ground states are predicted, in agreement with recent experimental investigations. The magnetic field and temperature scalings of the polarization, as well as the magnetic field dependence of the spin-flip gap are studied.

By following an exact analytical procedure we study the transmission properties of a network of quantum wires arranged in a so-called T3 configuration and in the presence of a perpendicular magnetic field. It is shown that proper use of a single unit cell is sufficient to demonstrate a recently discovered localization phenomenon for all wavelengths and for special values of the external field. This Aharonov-Bohm localization is shown to be independent of a vertex coupling that appears as a free parameter in the probability flux conservation. © 2002 Elsevier Science B.V. All rights reserved. 302 1 39 47 Cited By :1

Flux expulsion in a type-I superconducting strip, induced by decrease of a perpendicular magnetic field following field increase-induced flux penetration, is observed by real time detection of the flux-induced voltage pulses. Three different expulsion regimes are identified, corresponding in general to the three initial regimes of flux penetration. The crossover field between two expulsion regimes is found to be associated with the change of nucleation mechanism at Hc2. Possible association of the expulsion onset with surface superconductivity and Hc3 is discussed. The results support the idea of existence of an energy barrier against flux expulsion.

Localised-orbital analysis of the current density induced by a perpendicular magnetic field in square-planar Al 4 2− demonstrates the intrinsic non-localisability of the σ electrons of this metallic cluster and confirms their dominant role in its diamagnetic ring current. Though delocalised, the π electrons do not give rise to a significant ring current.

Transport of electrons through two-dimensional semiconductor structures on the nanoscale in the presence of perpendicular magnetic field depends on the interplay of geometry of the system, the leads, and the magnetic length. We use a generalized master equation (GME) formalism to describe the transport through the system without resorting to the Markov approximation. Coupling to the leads results in elastic and inelastic processes in the system that are described to a high order by the integro-differential equation of the GME formalism. Geometrical details of systems and leads leave their fingerprints on the transport of electrons through them. The GME formalism can be used to describe both the initial transient regime immediately after the coupling of the leads to the system and the steady state achieved after a longer time., Elsarticle pdfLaTeX, 3 pages with 6 png-figures included, Contribution to CCP-2009, submitted to Computer Physics Communications

Stochastic transport of a two-dimensional (2D) dusty plasma liquid with a perpendicular magnetic field is studied. Superdiffusion is found to occur especially at higher magnetic fields with $\ensuremath{\beta}$ of order unity. Here, $\ensuremath{\beta}={\ensuremath{\omega}}_{c}/{\ensuremath{\omega}}_{pd}$ is the ratio of the cyclotron and plasma frequencies for dust particles. The mean-square displacement $\mathrm{MSD}=4{D}_{\ensuremath{\alpha}}{t}^{\ensuremath{\alpha}}$ is found to have an exponent $\ensuremath{\alpha}g1$, indicating superdiffusion, with $\ensuremath{\alpha}$ increasing monotonically to $1.1$ as $\ensuremath{\beta}$ increases to unity. The 2D Langevin molecular dynamics simulation used here also reveals that another indicator of random particle motion, the velocity autocorrelation function, has a dominant peak frequency ${\ensuremath{\omega}}_{\text{peak}}$ that empirically obeys ${\ensuremath{\omega}}_{\text{peak}}^{2}={\ensuremath{\omega}}_{c}^{2}+{\ensuremath{\omega}}_{pd}^{2}/4$.

where ħω c 1⁄4 ejBzj=m eff . Accordingly, the second sentence below Eq. (2) should read as follows: “The next term ~ Hvl 1⁄4 τ 2 ~ gvlμBBz breaks the valley symmetry of Landau levels.” The ~ gvl values shown in the first row of Table II of the manuscript need to be corrected because they are actually half of the correct values. In addition, a minus-sign change comes from the above-mentioned redefinition of ~ gvl. Furthermore, since gvl in Eq. (4) is defined through ~ gvl, both its definition and its values (shown in the third row of Table II) are also modified. After redefinition, gvl is given by gvl 1⁄4 ð2me=meffÞ þ ~ gvl. The new Table II of the manuscript, with the corrected values of the valley g factors ~ gvl and gvl, is shown below. Note that the spin g factors g⊥so and g⊥sp do not need to be changed. Some of the gvl values also appear in the captions of Figs. 5 and 6, which therefore also need to be corrected. The caption of Fig. 5 should read as follows. “Spectrum of a 40-nmWS2 quantum dot as a function of the perpendicular magnetic field Bz > 0. Black (red) lines show the spin ↑ (↓) states from the valley K (K0). The values ofm eff can be found in Table I, whereas gvl 1⁄4 −3.36 and g⊥sp 1⁄4 1.99 (see Table II).”

The effect of a perpendicular magnetic field on the quantized current induced by a surface acoustic wave in a quasi-one-dimensional channel is studied. The channel was defined in a GaAs heterostructure by a shallow-etching technique. The quantized current in this constriction displayed superior precision (\ifmmode\pm\else\textpm\fi{}60 ppm) and robustness to dc bias relative to that observed previously in Schottky-gate-defined channels. In a perpendicular magnetic field commensurability oscillations were observed in the interval of current between quantized plateaus. The phase of the oscillations changes when a plateau is approached, which leads to an oscillatory change in the slope of the plateaus.

In a quasi-two-dimensional ~2D! electron system under a perpendicular magnetic field, we have observed resonant interaction between intersubband Bernstein modes and coupled intersubband-plasmon–LO-phonon modes. By changing parameters of the 2D electron system, a transition from strong to weak regimes of coupling between the plasmon and LO phonon was considered. In the strong-coupling regime, we have observed a double-resonance splitting of the first intersubband Bernstein mode with both intersubbandplasmon–LO-phonon modes, whereas in the weak-coupling regime only a single resonance splitting with the intersubband-plasmon-like mode has been found.

Microwave frequency conductivity $\mathrm{Re}({\ensuremath{\sigma}}_{\mathrm{xx}})$ of high quality two-dimensional hole systems (2DHS) in a large perpendicular magnetic field (B) is measured with the carrier density ${(n}_{s})$ of the 2DHS controlled by a backgate bias. The high-$B$ insulating phase of the 2DHS exhibits a microwave resonance that remains well defined, but shifts to higher peak frequency ${(f}_{\mathrm{pk}})$ as ${n}_{s}$ is reduced. In different regimes, ${f}_{\mathrm{pk}}$ vs ${n}_{s}$ can be fit to ${f}_{\mathrm{pk}}\ensuremath{\propto}{n}_{s}^{\ensuremath{-}1/2}$ or to ${f}_{\mathrm{pk}}\ensuremath{\propto}{n}_{s}^{\ensuremath{-}3/2}.$ The data clearly indicate that both carrier-carrier interactions and disorder are indispensable in determining the dynamics of the insulator. The ${n}_{s}$ dependence of ${f}_{\mathrm{pk}}$ is consistent with a weakly pinned Wigner crystal in which domain size increases with ${n}_{s},$ due to larger carrier-carrier interaction.

Electron scattering from two scatterers in tunnel-coupled double quantum wires (DQW) in a perpendicular magnetic field is considered. It is shown that in the partial energy gap, where there is only one propagating mode, the scattering from a pair of scatterers located in the opposite wires at a small distance from each other should exhibit the giant interference effect. The localization length in the DQW with disorder, modeled by an array of random short-range defects, is calculated for different concentrations of defects. At high concentrations the localization length is strongly reduced because of the enhanced scattering on pairs of nearby scatterers.

We find that a 2D periodic potential with different modulation amplitudes in x- and y-direction and a perpendicular magnetic field may lead to a transition to electron transport along the direction of stronger modulation and to localization in the direction of weaker modulation. In the experimentally accessible regime we relate this new quantum transport phenomenon to avoided band crossing due to classical chaos., 4 pages, 3 figures, minor modifications, PRL to appear

Coupling through random superconducting bridges between filaments in a multifilamentary Ag-sheathed Bi2Sr2Ca2Cu3O10+ tape has been investigated by magneto-optical imaging at temperatures from 20 K up to Tc. Magnetic flux distributions have been measured on the surface of an intact tape in the remanent state on applying a strong perpendicular magnetic field. The flux distributions observed at low temperatures reflect the arrangement of individual filaments. At high temperatures, the distribution becomes more similar to that for a uniform monocore tape, indicating that superconducting connections appear between the filaments. To discuss the relative contributions of the intra- and inter-filament currents, a simple model based on the Bean critical state was proposed and applied to analyse the temperature dependent behaviour. The inter-filament coupling, increasing with temperature, reaches at 77 K a point where the currents flowing in large inter-filament loops are roughly equal to the intra-filament currents.

We present a detailed investigation of excitonic absorption in $Zn_{0.69}Cd_{0.31}Se/ZnSe$ quantum wells under the application of a perpendicular magnetic field. The large energy separation between heavy- and light-hole excitons allows us to clearly resolve and identify magneto-excitonic absorption resonant with the continuum edge of the 1S heavy-hole exciton. Experimental values of the exciton binding energy are compared with results of a theoretical model that includes the exciton-phonon interaction. The remarkable agreemeent found unambiguously indicates the predominant polaronic character of excitons in ZnSe-based heterostructures.