1,065 research outputs found
Quantum Geometry and Thermal Radiation from Black Holes
A quantum mechanical description of black hole states proposed recently
within non-perturbative quantum gravity is used to study the emission and
absorption spectra of quantum black holes. We assume that the probability
distribution of states of the quantum black hole is given by the ``area''
canonical ensemble, in which the horizon area is used instead of energy, and
use Fermi's golden rule to find the line intensities. For a non-rotating black
hole, we study the absorption and emission of s-waves considering a special set
of emission lines. To find the line intensities we use an analogy between a
microscopic state of the black hole and a state of the gas of atoms.Comment: 19 pages, 4 figures, modified version to appear in Class. Quant. Gra
A Lattice Model of Intercalation
The thermodynamics of the lattice model of intercalation of ions in crystals
is considered in the mean field approximation. Pseudospin formalism is used for
the description of interaction of electrons with ions and the possibility of
hopping of intercalated ions between different positions is taken into account.
Phase diagrams are built. It is shown that the effective interaction between
intercalated ions can lead to phase separation or to appearance of modulated
phase (it depends on filling of the electron energy band). At high values of
the parameter of ion transfer the ionic subsystem can pass to the
superfluid-like state
Single fluxon in double stacked Josephson junctions: Analytic solution
We derive an approximate analytic solution for a single fluxon in a double
stacked Josephson junctions (SJJ's) for arbitrary junction parameters and
coupling strengths. It is shown that the fluxon in a double SJJ's can be
characterized by two components, with different Swihart velocities and
Josephson penetration depths. Using the perturbation theory we find the second
order correction to the solution and analyze its accuracy. Comparison with
direct numerical simulations shows a quantitative agreement between exact and
approximate analytic solutions. It is shown that due to the presence of two
components, the fluxon in SJJ's may have an unusual shape with an inverted
magnetic field in the second junction when the velocity of the fluxon is
approaching the lower Swihart velocity.Comment: 4 pages, 3 figure
The shape of a moving fluxon in stacked Josephson junctions
We study numerically and analytically the shape of a single fluxon moving in
a double stacked Josephson junctions (SJJ's) for various junction parameters.
We show that the fluxon in a double SJJ's consists of two components, which are
characterized by different Swihart velocities and Josephson penetration depths.
The weight coefficients of the two components depend on the parameters of the
junctions and the velocity of the fluxon. It is shown that the fluxon in SJJ's
may have an unusual shape with an inverted magnetic field in the second
junction when the velocity of the fluxon is approaching the lower Swihart
velocity. Finally, we study the influence of fluxon shape on flux-flow
current-voltage characteristics and analyze the spectrum of Cherenkov radiation
for fluxon velocity above the lower Swihart velocity. Analytic expression for
the wavelength of Cherenkov radiation is derived.Comment: 12 pages, 12 figure
In-plane fluxon in layered superconductors with arbitrary number of layers
I derive an approximate analytic solution for the in-plane vortex (fluxon) in
layered superconductors and stacked Josephson junctions (SJJ's) with arbitrary
number of layers. The validity of the solution is verified by numerical
simulation. It is shown that in SJJ's with large number of thin layers,
phase/current and magnetic field of the fluxon are decoupled from each other.
The variation of phase/current is confined within the Josephson penetration
depth, , along the layers, while magnetic field decays at the
effective London penetration depth, . For comparison
with real high- superconducting samples, large scale numerical simulations
with up to 600 SJJ's and with in-plane length up to 4000 %, are
presented. It is shown, that the most striking feature of the fluxon is a
Josephson core, manifesting itself as a sharp peak in magnetic induction at the
fluxon center.Comment: 4 pages, 4 figures. Was presented in part at the First Euroconference
on Vortex Matter in Superconductors (Crete, September 1999
On the Nature of Black Holes in Loop Quantum Gravity
A genuine notion of black holes can only be obtained in the fundamental
framework of quantum gravity resolving the curvature singularities and giving
an account of the statistical mechanical, microscopic degrees of freedom able
to explain the black hole thermodynamical properties. As for all quantum
systems, a quantum realization of black holes requires an operator algebra of
the fundamental observables of the theory which is introduced in this study
based on aspects of loop quantum gravity. From the eigenvalue spectra of the
quantum operators for the black hole area, charge and angular momentum, it is
demonstrated that a strict bound on the extensive parameters, different from
the relation arising in classical general relativity, holds, implying that the
extremal black hole state can neither be measured nor can its existence be
proven. This is, as turns out, a result of the specific form of the chosen
angular momentum operator and the corresponding eigenvalue spectrum, or rather
the quantum measurement process of angular momentum. Quantum mechanical
considerations and the lowest, non-zero eigenvalue of the loop quantum gravity
black hole mass spectrum indicate, on the one hand, a physical Planck scale
cutoff of the Hawking temperature law and, on the other hand, give upper and
lower bounds on the numerical value of the Immirzi parameter. This analysis
provides an approximative description of the behavior and the nature of quantum
black holes
Superconducting quantum interference phenomenon in BiSrCaCuO single crystals
The operational dc-SQUID based on intrinsic Josephson junctions in
BiSrCaCu2O high- superconductor is fabricated and
studied. The novel in-plane loop layout and the developed in-situ endpoint
detection method allowed an accurate control of the number of junctions in the
SQUID. A clear periodic modulation of the superconducting current as a function
of magnetic flux through the SQUID loop is observed. This is an unambiguous
evidence for the quantum interference phenomenon in
BiSrCaCu2O single crystals.Comment: 3 pages, 3 figure
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