4,224 research outputs found
SO(5) superconductor in a Zeeman magnetic field: Phase diagram and thermodynamic properties
In this paper we present calculations of the SO(5) quantum rotor theory of
high-T superconductivity in Zeeman magnetic field. We use the spherical
approach for five-component quantum rotors in three-dimensional lattice to
obtain formulas for critical lines, free energy, entropy and specific heat and
present temperature dependences of these quantities for different values of
magnetic field. Our results are in qualitative agreement with relevant
experiments on high-T cuprates.Comment: 4 pages, 2 figures, to appear in Phys. Rev. B, see http://prb.aps.or
Dependence of the superconducting critical temperature on the number of layers in homologous series of high-Tc cuprates
We study a model of -layer high-temperature cuprates of homologous series
like HgBa_2Ca_(n-1)Cu_nO_(2+2n+\delta) to explain the dependence of the
critical temperature Tc(n) on the number of Cu-O planes in the elementary
cell. Focusing on the description of the high-temperature superconducting
system in terms of the collective phase variables, we have considered a
semi-microscopic anisotropic three-dimensional vector XY model of stacked
copper-oxide layers with adjustable parameters representing microscopic
in-plane and out-of-plane phase stiffnesses. The model captures the layered
composition along c-axis of homologous series and goes beyond the
phenomenological Lawrence-Doniach model for layered superconductors.
Implementing the spherical closure relation for vector variables we have solved
the phase XY model exactly with the help of transfer matrix method and
calculated Tc(n) for arbitrary block size , elucidating the role of the
c-axis anisotropy and its influence on the critical temperature. Furthermore,
we accommodate inhomogeneous charge distribution among planes characterized by
the charge imbalance coefficient being the function of number of layers
. By making a physically justified assumption regarding the doping
dependence of the microscopic phase stiffnesses, we have calculated the values
of parameter as a function of block size in good agreement with the
nuclear magnetic resonance data of carrier distribution in multilayered high-Tc
cuprates.Comment: 15 pages, 10 figures. Submitted to Physical Review
Collective patterns arising out of spatio-temporal chaos
We present a simple mathematical model in which a time averaged pattern
emerges out of spatio-temporal chaos as a result of the collective action of
chaotic fluctuations. Our evolution equation possesses spatial translational
symmetry under a periodic boundary condition. Thus the spatial inhomogeneity of
the statistical state arises through a spontaneous symmetry breaking. The
transition from a state of homogeneous spatio-temporal chaos to one exhibiting
spatial order is explained by introducing a collective viscosity which relates
the averaged pattern with a correlation of the fluctuations.Comment: 11 pages (Revtex) + 5 figures (postscript
On the dynamics of a collapsing bubble in contact with a rigid wall
This work reveals that the dynamic response of a spherical cap bubble in
contact with a rigid wall depends on the effective contact angle at the instant
prior to collapse. This parameter allows us to discriminate between two regimes
in which the mechanisms of interaction between the collapsing bubble and its
surrounding medium differ significantly: When the contact angle is smaller than
90 degrees a classical jet directed towards the wall is observed whereas if the
initial contact angle is larger than 90 degrees an annular re-entrant jet
parallel to the wall appears. We show that this change of the behaviour can be
explained using the impulse potential flow theory for small times which shows
the presence of a singularity on the initial acceleration of the contact line
when the contact angle is larger then 90 degrees. Direct Numerical Simulations
show that although viscosity regularises the solution at , the solution
remains singular at . In these circumstances numerical and experimental
results show that the collapse of flat bubbles can eventually lead to the
formation of a vortex ring that unexpectedly induces long-range effects. The
role of the bubble geometry at the instant of maximum expansion on the overall
collapse process is shown to be well captured by the impulse potential flow
theory, which can be easily generalised to other bubble shapes. These results
may find direct application in the interpretation of geophysical flows as well
as the control and design of bio-medical, naval, manufacturing and
sonochemistry applications
Overview of the BlockNormal Event Trigger Generator
In the search for unmodeled gravitational wave bursts, there are a variety of
methods that have been proposed to generate candidate events from time series
data. Block Normal is a method of identifying candidate events by searching for
places in the data stream where the characteristic statistics of the data
change. These change-points divide the data into blocks in which the
characteristics of the block are stationary. Blocks in which these
characteristics are inconsistent with the long term characteristic statistics
are marked as Event-Triggers which can then be investigated by a more
computationally demanding multi-detector analysis.Comment: GWDAW-8 proceedings, 6 pages, 2 figure
AC losses and critical current density of superconducting GdBa2Cu3O7−x
Energy losses occurring in a cylindrical sample of Gd-Ba-Cu-O, subjected to an external AC magnetic field were examined. The loss dependence on the amplitude of the magnetic induction exhibits two stages of flux penetration into the superconductor. Critical current densitities for both stages of penetration were examined and an explanation for such behaviour is proposed. Support for this point of view is obtained by measurements on pulverized sample material. All measurements were performed at a temperature of 4.2 K and in absence of a background field.\ud
\ud
Analysis of the data provides two critical current densities: an inter-granular critical current density at weak alternating magnetic fields and an intra-granular critical current density at higher magnetic fields. The intra-granular critical current density is at least two orders of magnitude larger than the inter-granular one
- …