7,544 research outputs found
Transition behavior of k-surface from hyperbola to ellipse
The transition behavior of the k-surface of a lossy anisotropic indefinite slab is investigated. It is found that, if the material loss is taken into account, the k-surface does not show a sudden change from hyperbola to the ellipse when one principle element of the permittivity tensor changes from negative to positive. In fact, after introducing a small material loss, the shape of the k-surface can be a combination of a hyperbola and an ellipse, and a selective high directional transmission can be obtained in such a slab
Crystal growth and annealing study of fragile, non-bulk superconductivity in YFeGe
We investigated the occurrence and nature of superconductivity in single
crystals of YFeGe grown out of Sn flux by employing x-ray diffraction,
electrical resistivity, and specific heat measurements. We found that the
residual resistivity ratio (RRR) of single crystals can be greatly improved,
reaching as high as 60, by decanting the crystals from the molten Sn at
350C and/or by annealing at temperatures between 550C and
600C. We found that samples with RRR 34 showed resistive
signatures of superconductivity with the onset of the superconducting
transition K. RRR values vary between 35 and 65 with, on
average, no systematic change in value, indicating that systematic
changes in RRR do not lead to comparable changes in . Specific heat
measurements on samples that showed clear resistive signatures of a
superconducting transition did not show any signature of a superconducting
phase transition, which suggests that the superconductivity observed in this
compound is either some sort of filamentary, strain stabilized
superconductivity associated with small amounts of stressed YFeGe
(perhaps at twin boundaries or dislocations) or is a second crystallographic
phase present at levels below detection capability of conventional powder x-ray
techniques.Comment: 8 pages, 11 figure
Andreev Reflection without Fermi surface alignment in High T-Topological heterostructures
We address the controversy over the proximity effect between topological
materials and high T superconductors. Junctions are produced between
BiSrCaCuO and materials with different Fermi
surfaces (BiTe \& graphite). Both cases reveal tunneling spectra
consistent with Andreev reflection. This is confirmed by magnetic field that
shifts features via the Doppler effect. This is modeled with a single parameter
that accounts for tunneling into a screening supercurrent. Thus the tunneling
involves Cooper pairs crossing the heterostructure, showing the Fermi surface
mis-match does not hinder the ability to form transparent interfaces, which is
accounted for by the extended Brillouin zone and different lattice symmetries
Pairing in the iron arsenides: a functional RG treatment
We study the phase diagram of a microscopic model for the superconducting
iron arsenides by means of a functional renormalization group. Our treatment
establishes a connection between a strongly simplified two-patch model by
Chubukov et al. and a five-band- analysis by Wang et al.. For a wide parameter
range, the dominant pairing instability occurs in the extended s-wave channel.
The results clearly show the relevance of pair scattering between electron and
hole pockets. We also give arguments that the phase transition between the
antiferromagnetic phase for the undoped system and the superconducting phase
may be first order
Investigation of multi-phase tubular permanent magnet linear generator for wave energy converters
In this article, an investigation into different magnetization topologies for a long stator tubular permanent magnet linear generator is performed through a comparison based on the cogging force disturbance, the power output, and the cost of the raw materials of the machines. The results obtained from finite element analysis simulation are compared with an existing linear generator described in [1]. To ensure accurate results, the generator developed in [1] is built with 3D CAD and simulated using the finite-element method, and the obtained results are verified with the source.The PRIMaRE project
Evolution of ground state and upper critical field in R(1-x)GdxNi2B2C (R = Lu, Y): Coexistence of superconductivity and spin-glass state
We report effects of local magnetic moment, Gd3+, doping (x =< 0.3) on
superconducting and magnetic properties of the closely related Lu(1-x)GdxNi2B2C
and Y(1-x)GdxNi2B2C series. The superconducting transition temperature
decreases and the heat capacity jump associated with it drops rapidly with
Gd-doping; qualitative changes with doping are also observed in the
temperature-dependent upper critical field behavior, and a region of
coexistence of superconductivity and spin-glass state is delineated on the x -
T phase diagram. The evolution of superconducting properties can be understood
within Abrikosov-Gor'kov theory of magnetic impurities in superconductors
taking into account the paramagnetic effect on upper critical field with
additional contributions particular for the family under study
Quantum spin liquid states in the two dimensional kagome antiferromagnets, ZnxCu4-x(OD)6Cl2
A three-dimensional system of interacting spins typically develops static
long-range order when it is cooled. If the spins are quantum (S = 1/2),
however, novel quantum paramagnetic states may appear. The most highly sought
state among them is the resonating valence bond (RVB) state in which every pair
of neighboring quantum spins form entangled spin singlets (valence bonds) and
the singlets are quantum mechanically resonating amongst all the possible
highly degenerate pairing states. Here we provide experimental evidence for
such quantum paramagnetic states existing in frustrated antiferromagnets,
ZnxCu4-x(OD)6Cl2, where the S = 1/2 magnetic Cu2+ moments form layers of a
two-dimensional kagome lattice. We find that in Cu4(OD)6Cl2, where distorted
kagome planes are weakly coupled to each other, a dispersionless excitation
mode appears in the magnetic excitation spectrum below ~ 20 K, whose
characteristics resemble those of quantum spin singlets in a solid state, known
as a valence bond solid (VBS), that breaks translational symmetry. Doping
nonmagnetic Zn2+ ions reduces the distortion of the kagome lattice, and weakens
the interplane coupling but also dilutes the magnetic occupancy of the kagome
lattice. The VBS state is suppressed and for ZnCu3(OD)6Cl2 where the kagome
planes are undistorted and 90% occupied by the Cu2+ ions, the low energy spin
fluctuations in the spin liquid phase become featureless
One-dimensional hydrogen atom with minimal length uncertainty and maximal momentum
We present exact energy eigenvalues and eigenfunctions of the one-dimensional
hydrogen atom in the framework of the Generalized (Gravitational) Uncertainty
Principle (GUP). This form of GUP is consistent with various theories of
quantum gravity such as string theory, loop quantum gravity, black-hole
physics, and doubly special relativity and implies a minimal length uncertainty
and a maximal momentum. We show that the quantized energy spectrum exactly
agrees with the semiclassical results.Comment: 10 pages, 1 figur
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