3,271 research outputs found
Competing Boundary Interactions in a Josephson Junction Network with an Impurity
We analyze a perturbation of the boundary Sine-Gordon model where two
boundary terms of different periodicities and scaling dimensions are coupled to
a Kondo-like spin degree of freedom. We show that, by pertinently engineering
the coupling with the spin degree of freedom, a competition between the two
boundary interactions may be induced, and that this gives rise to
nonpertubative phenomena, such as the emergence of novel quantum phases:
indeed, we demonstrate that the strongly coupled fixed point may become
unstable as a result of the "deconfinement" of a new set of phase-slip
operators -the short instantons- associated with the less relevant boundary
operator.
We point out that a Josephson junction network with a pertinent impurity
located at its center provides a physical realization of this boundary double
Sine-Gordon model. For this Josephson junction network, we prove that the
competition between the two boundary interactions stabilizes a robust finite
coupling fixed point and, at a pertinent scale, allows for the onset of
superconductivity.Comment: 43 pages, 12 figure
A fingerprint based metric for measuring similarities of crystalline structures
Measuring similarities/dissimilarities between atomic structures is important
for the exploration of potential energy landscapes. However, the cell vectors
together with the coordinates of the atoms, which are generally used to
describe periodic systems, are quantities not suitable as fingerprints to
distinguish structures. Based on a characterization of the local environment of
all atoms in a cell we introduce crystal fingerprints that can be calculated
easily and allow to define configurational distances between crystalline
structures that satisfy the mathematical properties of a metric. This distance
between two configurations is a measure of their similarity/dissimilarity and
it allows in particular to distinguish structures. The new method is an useful
tool within various energy landscape exploration schemes, such as minima
hopping, random search, swarm intelligence algorithms and high-throughput
screenings
From propagators to glueballs in the Gribov-Zwanziger framework
Over the last years, lattice calculations in pure Yang-Mills gauge theory
seem to have come more or less to a consensus. The ghost propagator is not
enhanced and the gluon propagator is positivity violating, infrared suppressed
and non-vanishing at zero momentum. From an analytical point of view, several
groups are agreeing with these results. Among them, the refined
Gribov-Zwanziger (RGZ) framework also accommodates for these results. The
question which rises next is, if our models hold the right form for the
propagators, how to extract information on the real physical observables, i.e.
the glueballs? How do the operators which represent glueballs look like? We
review the current status of this matter within the RGZ framework.Comment: 3 pages, Conference contribution for Confinement IX, Madrid 2010
(30/08-03/09), to appear in American Institute of Physics (AIP
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