5,536 research outputs found
Analytical investigation of magnetic field distributions around superconducting strips on ferromagnetic substrates
The complex-field approach is developed to derive analytical expressions of
the magnetic field distributions around superconducting strips on ferromagnetic
substrates (SC/FM strips). We consider the ferromagnetic substrates as ideal
soft magnets with an infinite magnetic permeability, neglecting the
ferromagnetic hysteresis. On the basis of the critical state model for a
superconducting strip, the ac susceptibility of a SC/FM
strip exposed to a perpendicular ac magnetic field is theoretically
investigated, and the results are compared with those for superconducting
strips on nonmagnetic substrates (SC/NM strips). The real part for
(where is the amplitude of the ac magnetic field,
is the critical current density, and is the thickness of the
superconducting strip) of a SC/FM strip is 3/4 of that of a SC/NM strip. The
imaginary part (or ac loss ) for of a SC/FM
strip is larger than that of a SC/NM strip, even when the ferromagnetic
hysteresis is neglected, and this enhancement of (or ) is due to
the edge effect of the ferromagnetic substrate.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
Uniqueness of static spherically symmetric vacuum solutions in the IR limit of Ho\v{r}ava-Lifshitz gravity
We investigate static spherically symmetric vacuum solutions in the IR limit
of projectable nonrelativistic quantum gravity, including the renormalisable
quantum gravity recently proposed by Ho\v{r}ava. It is found that the
projectability condition plays an important role. Without the cosmological
constant, the spacetime is uniquely given by the Schwarzschild solution. With
the cosmological constant, the spacetime is uniquely given by the Kottler
(Schwarzschild-(anti) de Sitter) solution for the entirely vacuum spacetime.
However, in addition to the Kottler solution, the static spherical and
hyperbolic universes are uniquely admissible for the locally empty region, for
the positive and negative cosmological constants, respectively, if its
nonvanishing contribution to the global Hamiltonian constraint can be
compensated by that from the nonempty or nonstatic region. This implies that
static spherically symmetric entirely vacuum solutions would not admit the
freedom to reproduce the observed flat rotation curves of galaxies. On the
other hand, the result for locally empty regions implies that the IR limit of
nonrelativistic quantum gravity theories does not simply recover general
relativity but includes it.Comment: 10 pages, accepted for publication in International Journal of Modern
Physics
The spin-incoherent Luttinger liquid
In contrast to the well known Fermi liquid theory of three dimensions,
interacting one-dimensional and quasi one-dimensional systems of fermions are
described at low energy by an effective theory known as Luttinger liquid
theory. This theory is expressed in terms of collective many-body excitations
that show exotic behavior such as spin-charge separation. Luttinger liquid
theory is commonly applied on the premise that "low energy" describes both the
spin and charge sectors. However, when the interactions in the system are very
strong, as they typically are at low particle densities, the ratio of spin to
charge energy may become exponentially small. It is then possible at very low
temperatures for the energy to be low compared to the characteristic charge
energy, but still high compared to the characteristic spin energy. This energy
window of near ground-state charge degrees of freedom, but highly thermally
excited spin degrees of freedom is called a spin-incoherent Luttinger liquid.
The spin-incoherent Luttinger liquid exhibits a higher degree universality than
the Luttinger liquid and its properties are qualitatively distinct. In this
colloquium I detail some of the recent theoretical developments in the field
and describe experimental indications of such a regime in gated semiconductor
quantum wires.Comment: 21 pages, 18 figures. Updated references, corrected typo in Eq.(20)
in journal versio
Quantum Monte Carlo simulation of S=1/2 Heisenberg model with four spin interaction
25th International Conference on Low Temperature Physics (LT25)The spin S = 1/2 Heisenberg model with four-spin interaction on the square lattice is studied by using quantum Monte Carlo method. When the four-spin interaction is dominant, the system has a VBS ground state. In this case, we find a finite-temperature second-order phase transition to the VBS state. The universality class of the transition is investigated. We estimate the critical exponents ν and η from the finite size scaling analysis and find ν = 0.68(1) and η = 0.55(2)
Statistical Analysis of Surface Reconstruction Domains on InAs Wetting Layer Preceding Quantum Dot Formation
Surface of an InAs wetting layer on GaAs(001) preceding InAs quantum dot (QD) formation was observed at 300°C with in situ scanning tunneling microscopy (STM). Domains of (1 × 3)/(2 × 3) and (2 × 4) surface reconstructions were located in the STM image. The density of each surface reconstruction domain was comparable to that of subsequently nucleated QD precursors. The distribution of the domains was statistically investigated in terms of spatial point patterns. It was found that the domains were distributed in an ordered pattern rather than a random pattern. It implied the possibility that QD nucleation sites are related to the surface reconstruction domains
Can we distinguish between black holes and wormholes by their Einstein-ring systems?
For the last decade, the gravitational lensing in the strong gravitational
field has been studied eagerly. It is well known that, for the lensing by a
black hole, infinite number of Einstein rings are formed by the light rays
which wind around the black hole nearly on the photon sphere, which are called
relativistic Einstein rings. This is also the case for the lensing by a
wormhole. In this paper, we study the Einstein ring and relativistic Einstein
rings for the Schwarzschild black hole and the Ellis wormhole, the latter of
which is an example of traversable wormholes of the Morris-Thorne class. Given
the configuration of the gravitational lensing and the radii of the Einstein
ring and relativistic Einstein rings, we can distinguish between a black hole
and a wormhole in principle. We conclude that we can detect the relativistic
Einstein rings by wormholes which have the radii of the throat pc
at a galactic center with the distance 10Mpc and which have AU in
our galaxy using by the most powerful modern instruments which have the
resolution of arcsecond such as a 10-meter optical-infrared telescope.
The black holes which make the Einstein rings of the same size as the ones by
the wormholes are galactic supermassive black holes and the relativistic
Einstein rings by the black holes are too small to measure at this moment. We
may test some hypotheses of astrophysical wormholes by using the Einstein ring
and relativistic Einstein rings in the future.Comment: 13 pages, 2 figures, minor changes from v
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