Hall Configuration Research Articles

Quantitative analysis of the guidance of vortices in superconducting films with magnetic dots

The guidance of vortices in superconducting Nb films with periodic arrangements of magnetic Ni dots is studied via simultaneous four-probe measurements in standard and Hall configuration. Ni dots are fabricated via e-beam lithography and lift-off technology. Arrays with periodicity down to 400 nm and dot size of 200 nm are obtained. Subsequently, the arrays are covered with a thin superconducting Nb layer. Simultaneous Hall and standard resistive measurements of the flux dynamic in Nb bridges with and without magnetic dots demonstrate and quantify the guidance of flux via the magnetic dots. Guidance of vortices is only possible in a limited current regime; guidance improves with decreasing temperature. Within the identified current regime most of the vortices (>40% for zero field) and in the optimum case all of the vortices are guided by the magnetic dots.

Nonmonotonic behavior of magnetophotoconductivity in p-CdHgTe

Magnetophotoconductivity of p-CdxHg1−xTe, measured in the Hall configuration with illumination along the magnetic field (k ∥ B ⊥ E), exhibits nonmonotonic behavior with magnetic field in the temperature range in which the material has a mixed conduction. The effect manifests itself as a peak at B ≠ 0; it is caused by a significant magnetoresistance associated with equilibrium charge carriers. The peak appears if the conductivity of equilibrium electrons is greater than or equal to half the conductivity of equilibrium heavy holes; in CdxHg1−x Te with x = 0.22, this condition is satisfied at temperatures of 140–150 K.

Time-dependent Ginzburg–Landau equations with charged boundaries

We build a discrete form for the Ginzburg–Landau thermodynamic potential for an infinite film and find how the TDGL equations are related to it. We discuss why the usual superconductor-insulator boundary condition, which prohibits the passage of superconducting current, should be questioned in dynamic problems; nevertheless, we conclude that this condition remains valid. The formalism we develop enables us to deal with situations in which surface charge is present at the boundaries. These situations include the Hall configuration when the influence of the normal electrons is not negligible and the case of an electromagnetic wave parallel to the film. In the case of the electromagnetic wave, we evaluate the electromagnetic field inside the superconductor and follow the motion of the vortices.

Spontaneous superconducting islands and Hall voltage in superconductors with large electric penetration depth

We study a clean superconductor in the Hall configuration, in the framework of a purely dissipative time-dependent Ginzburg--Landau theory. We find situations in which the order parameter differs significantly from zero in a set of islands that appear to form a periodic structure. When the pattern of islands becomes irregular, it moves in or against the direction of the current and a Hall voltage is found. Tiny differences in the initial state may reverse the sign of the Hall voltage. When the average Hall voltage vanishes, the local Hall voltage does not necessarily vanish. We examine the influence that several boundary conditions at the electrodes have on these effects.

Electronic spectrum of a two-dimensional quantum dot array in the presence of electric and magnetic fields in the Hall configuration

We report calculations of the electronic spectrum of a two-dimensional lattice of coupled quantum dots, subject to external electric and magnetic fields in the Hall configuration. The quantum dots array was modeled by a periodic superposition of truncated, parabolic potential wells. By adopting the Landau gauge, a single-particle Hamiltonian was formulated, and its eigenfunctions were obtained as appropriately symmetrized, magnetic field-dependent Bloch functions. The magnetic field was consistently included in the corresponding Wannier functions, which were approximated by the eigenvectors of an isolated quantum dot in the presence of the external magnetic field, and multiplied by the Peierls's phase.

Transverse magnetovoltage in epitaxial La 0.67Ca 0.33MnO 3 thin films

We present detailed Hall effect, planar Hall effect and resistance measurements of an epitaxial La 0.67Ca 0.33MnO 3 thin film. In the ferromagnetic regime the transverse voltage shows a similar dependence on the external magnetic field when it is applied perpendicular to (Hall effect) and in the plane of the film (planar Hall effect). By this observation it is established that the anomalous Hall effect is not the main origin of the transverse magnetovoltage. It is the anisotropic magnetoresistance (AMR), which we observe in both the longitudinal and the planar Hall configuration that causes the transverse magnetovoltage.

Acoustical characteristics of a 360-degree surround hall

Boettcher Hall in Denver is a large multipurpose hall with audience seating completely surrounding the stage and has been described as a 360-deg surround hall. Extensive acoustical measurements were carried out to evaluate the characteristics of this hall configuration and to compare it to other halls of more conventional design. Impulse response measurements were made for the 45 combinations of three on-stage source positions and 15 receiver positions distributed throughout the audience seating area. The setup of the hall was representative of a typical unoccupied concert configuration. Measured parameters included octave band values of: reverberation times, early decay times, relative sound levels, and early/late sound ratios. Various measures of spatial impression were also measured including: lateral energy fractions, inter-aural cross correlations, and the newly proposed measure of listener envelopment, the late lateral sound level. Hall average values as well as the spatial variation of acoustical measures are compared to data obtained from a number of other halls. [Work supported by the Concert Hall Research Group.]

Dynamics of two interacting particles in a magnetic field in two dimensions

The classical dynamics of two interacting particles of equal mass and equal or opposite charge, moving in a plane and a perpendicular magnetic field, is discussed. The simplest trajectories are similar to those of a single particle in the presence of crossed electric and magnetic fields (Hall configuration). Such motion occurs over a ribbon that may be straight (for opposite charges), or bent into a circle (for identical particles).

Magnetotransport effects in the mixed state of heavy fermion superconductors

Magnetotransport effects have been investigated in polycrystalline samples of U 6Co and U 6Fe. The superconducting state data have been obtained in applied magnetic fields up to 9 T. U 6Co has a residual resistance ratio RRR(RT/4.2 K) = 2, T c = 2.44 K and ΔT c (10%–90%) = 105 mK. The U 6Fe sample has RRR = 7, T c = 3.95 K and ΔT c =40 mK. The magnetic thresholds are roughly the same either with the electrical contacts in the Hall configuration or in the resistivity configuration for the U 6Co sample, but they are clearly different for the U 6Fe sample, with the Hall thresholds lying below resistivity thresholds, similar to previous results for UBe 13obtained using the same technique.

Ionic and electronic transport in liquid metals: Relation between longitudinal and transverse effects

Utilizing relations due to Moreau and to Bridgman, plus the Wiedemann-Franz law, it is first demonstrated that a longitudinal effect, the Thomson thermoelectric coefficient, σ T is given by LP R , where L is the Lorenz number while P and R characterize transverse effects, represented by Ettingshausen and Hall coefficients, respectively. Corresponding effects are then defined for ionic transport, motivated by the observed Haeffrer effect for isotopes but written initially for an isotopically pure liquid metal. In this way, we have related a longitudinal ionic density gradient to a similar transverse gradient in the Hall configuration in a transverse magnetic field. The latter gradient is shown to be precisely determined by the ratio eE H k B T , where E H is the Hall electric field. Generalizing to a binary mixture of isotopes, the Haeffner effect follows directly by momentum transfer arguments.

Two-dimensional crystalline electrons in the Hall configuration.

The spectrum of an electron moving in a two-dimensional lattice subject to an electric field in the plane and a normal magnetic field is discussed. We show that the nature of the spectrum of a Landau level depends on the ratio of the Hall potential to the crystal bandwidth. When this ratio is small the density of states is similar to that in the absence of the electric field, and the wave functions spread throughout the crystal. When it is large the spectrum has no gaps, the density of states is periodic with a Wannier-Stark period, and the wave functions are localized in the direction of the electric field.

Dallas Brooks Hall, The Masonic Centre of Victoria, Melbourne, Australia

This paper discusses the room acoustics, sound-reinforcement system, and noise control of the Dallas Brooks Hall, a multipurpose hall utilized for Masonic functions, conferences, conventions, and exhibitions, in addition to its primary use as a concert hall. In the concert hall configuration, the hall, with a volume of 500 000 ft3, seats about 2000 people. Reverberation time is on the order of 2 sec at midfrequencies. The sound-reinforcement system employs a single cluster of low- and high-frequency loud-speakers. Supplementary cone-type loudspeakers are installed in the balcony soffits. The system is designed for even coverage and reinforcement with directional realism. A time-delay system is utilized with the underbalcony loudspeakers. Extensive noise-control treatments were incorporated in the air-handling systems to control the ambient-noise levels in the hall due to mechanical equipment. The actually measured ambient noise is below the NC-15 criterion curve. The noise-control treatment included dissipative silencers in the duct systems, low air speeds in the supply and return ducts, low slot velocities at the diffusers and return grilles, and vibration isolation of the machinery.

A discussion on advanced methods of energy conversion- Magnetohydrodynamic power generation - II. Recent progress in the development of combustion fired m .h.d. generators

This paper reports on some recent progress in the development of the large combustion fired m.h.d. generator with particular emphasis on commercial central station application. The segmented electrode Faraday configuration m.h.d. generator is highly efficient but has the disadvantage of delivering its output in a multiplicity of loads each of which floats at a different potential. For this reason our recent work in m.h.d. generator fluid mechanics and long duration channel development has been concentrated on examination of the high voltage two-terminal Hall configuration, and this work will be described. The chemistry and economics of seeding must be carefully evaluated in order to assess the potential of m.h.d. and the paper will describe recent work which has demonstrated the feasibility of efficient low cost seed recovery employing vapour phase separation. Superconducting field coils appear to be essential for commercial m.h.d. power generation and the ‘stabilized* principle of constructing such coils will be described. Using this principle it is possible to operate a large coil on the H — I curve of a short sample of wire. This development reduces the construction of large superconducting coils to an engineering problem.