890 research outputs found
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
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
Lambda<0 Quantum Gravity in 2+1 Dimensions II: Black Hole Creation by Point Particles
Using the recently proposed formalism for Lambda<0 quantum gravity in 2+1
dimensions we study the process of black hole production in a collision of two
point particles. The creation probability for a BH with a simplest topology
inside the horizon is given by the Liouville theory 4-point function projected
on an intermediate state. We analyze in detail the semi-classical limit of
small AdS curvatures, in which the probability is dominated by the exponential
of the classical Liouville action. The probability is found to be exponentially
small. We then argue that the total probability of creating a horizon given by
the sum of probabilities of all possible internal topologies is of order unity,
so that there is no exponential suppression of the total production rate.Comment: v1: 30+1 pages, figures, v2: 34+1 pages, agruments straightened ou
Holography for the Lorentz Group Racah Coefficients
A known realization of the Lorentz group Racah coefficients is given by an
integral of a product of 6 ``propagators'' over 4 copies of the hyperbolic
space. These are ``bulk-to-bulk'' propagators in that they are functions of two
points in the hyperbolic space. It is known that the bulk-to-bulk propagator
can be constructed out of two bulk-to-boundary ones. We point out that there is
another way to obtain the same object. Namely, one can use two bulk-to-boundary
and one boundary-to-boundary propagator. Starting from this construction and
carrying out the bulk integrals we obtain a realization of the Racah
coefficients that is ``holographic'' in the sense that it only involves
boundary objects. This holographic realization admits a geometric
interpretation in terms of an ``extended'' tetrahedron.Comment: 12 pages, 2 figures; v2: minor changes; v3: "extended" tetrahedron
interpretation adde
Interlayer tunneling spectroscopy of BiSrCaCuO: a look from inside on the doping phase diagram of high superconductors
A systematic, doping dependent interlayer tunneling spectroscopy of Bi2212
high superconductor is presented. An improved resolution made it possible
to simultaneously trace the superconducting gap (SG) and the normal state
pseudo-gap (PG) in a close vicinity of and to analyze closing of the PG
at . The obtained doping phase diagram exhibits a critical doping point
for appearance of the PG and a characteristic crossing of the SG and the PG
close to the optimal doping. This points towards coexistence of two different
and competing order parameters in Bi2212. Experimental data indicate that the
SG can form a combined (large) gap with the PG at and that the
interlayer tunneling becomes progressively incoherent with decreasing doping.Comment: 5 pages, 5 figure
New hydrogen-sensitive films based on V2O5 and WO3 with Pt catalyst
Optical properties of the films of vanadium and tungsten oxides in a gas atmosphere, containing hydrogen, have been investigated. Films have been synthesized by electrodeposition and chemical deposition from aqueous solutions. Vanadium (V) oxide films and tungsten (VI) oxide films with a platinum catalyst reversibly change their color being exposed to hydrogen. The present work show promising use for such films as sensitive optical elements for gas sensors
The Universal Phase Space of AdS3 Gravity
We describe what can be called the "universal" phase space of AdS3 gravity,
in which the moduli spaces of globally hyperbolic AdS spacetimes with compact
spatial sections, as well as the moduli spaces of multi-black-hole spacetimes
are realized as submanifolds. The universal phase space is parametrized by two
copies of the Universal Teichm\"uller space T(1) and is obtained from the
correspondence between maximal surfaces in AdS3 and quasisymmetric
homeomorphisms of the unit circle. We also relate our parametrization to the
Chern-Simons formulation of 2+1 gravity and, infinitesimally, to the
holographic (Fefferman-Graham) description. In particular, we obtain a relation
between the generators of quasiconformal deformations in each T(1) sector and
the chiral Brown-Henneaux vector fields. We also relate the charges arising in
the holographic description (such as the mass and angular momentum of an AdS3
spacetime) to the periods of the quadratic differentials arising via the Bers
embedding of T(1)xT(1). Our construction also yields a symplectic map from
T*T(1) to T(1)xT(1) generalizing the well-known Mess map in the compact spatial
surface setting.Comment: 41 pages, 2 figures, revised version accepted for publication in
Commun.Math.Phy
Unification of gravity, gauge fields, and Higgs bosons
We consider a diffeomorphism invariant theory of a gauge field valued in a
Lie algebra that breaks spontaneously to the direct sum of the spacetime
Lorentz algebra, a Yang-Mills algebra, and their complement. Beginning with a
fully gauge invariant action -- an extension of the Plebanski action for
general relativity -- we recover the action for gravity, Yang-Mills, and Higgs
fields. The low-energy coupling constants, obtained after symmetry breaking,
are all functions of the single parameter present in the initial action and the
vacuum expectation value of the Higgs.Comment: 12 pages, no figures. v2 minor correction
Quantum Geometry and Black Hole Entropy
A `black hole sector' of non-perturbative canonical quantum gravity is
introduced. The quantum black hole degrees of freedom are shown to be described
by a Chern-Simons field theory on the horizon. It is shown that the entropy of
a large non-rotating black hole is proportional to its horizon area. The
constant of proportionality depends upon the Immirzi parameter, which fixes the
spectrum of the area operator in loop quantum gravity; an appropriate choice of
this parameter gives the Bekenstein-Hawking formula S = A/4*l_p^2. With the
same choice of the Immirzi parameter, this result also holds for black holes
carrying electric or dilatonic charge, which are not necessarily near extremal.Comment: Revtex, 8 pages, 1 figur
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