9,175 research outputs found
Amorphous thin film growth: theory compared with experiment
Experimental results on amorphous ZrAlCu thin film growth and the dynamics of
the surface morphology as predicted from a minimal nonlinear stochastic
deposition equation are analysed and compared. Key points of this study are (i)
an estimation procedure for coefficients entering into the growth equation and
(ii) a detailed analysis and interpretation of the time evolution of the
correlation length and the surface roughness. The results corroborate the
usefulness of the deposition equation as a tool for studying amorphous growth
processes.Comment: 7 pages including 5 figure
Superconducting Puddles and "Colossal'' Effects in Underdoped Cuprates
Phenomenological models for the antiferromagnetic (AF) vs. d-wave
superconductivity competition in cuprates are studied using conventional Monte
Carlo techniques. The analysis suggests that cuprates may show a variety of
different behaviors in the very underdoped regime: local coexistence or
first-order transitions among the competing orders, stripes, or glassy states
with nanoscale superconducting (SC) puddles. The transition from AF to SC does
not seem universal. In particular, the glassy state leads to the possibility of
"colossal'' effects in some cuprates, analog of those in manganites. Under
suitable conditions, non-superconducting Cu-oxides could rapidly become
superconducting by the influence of weak perturbations that align the randomly
oriented phases of the SC puddles in the mixed state. Consequences of these
ideas for thin-film and photoemission experiments are discussed.Comment: RevTeX 4, revised expanded version, 8 pages, 8 figure
Phase Fluctuations in Strongly Coupled -Wave Superconductors
We present a numerically exact solution for the BCS Hamiltonian at any
temperature, including the degrees of freedom associated with classical phase,
as well as amplitude, fluctuations via a Monte Carlo (MC) integration. This
allows for an investigation over the whole range of couplings: from weak
attraction, as in the well-known BCS limit, to the mainly unexplored
strong-coupling regime of pronounced phase fluctuations. In the latter, for the
first time two characteristic temperatures and , associated with
short- and long-range ordering, respectively, can easily be identified in a
mean-field-motivated Hamiltonian. at the same time corresponds to the
opening of a gap in the excitation spectrum. Besides introducing a novel
procedure to study strongly coupled d-wave superconductors, our results
indicate that classical phase fluctuations are not sufficient to explain the
pseudo-gap features of high-temperature superconductors (HTS).Comment: 5 pages, 3 figure
Colossal Effects in Transition Metal Oxides Caused by Intrinsic Inhomogeneities
The influence of quenched disorder on the competition between ordered states
separated by a first-order transition is investigated. A phase diagram with
features resembling quantum-critical behavior is observed, even using classical
models. The low-temperature paramagnetic regime consists of coexisting ordered
clusters, with randomly oriented order parameters. Extended to manganites, this
state is argued to have a colossal magnetoresistance effect. A scale T* for
cluster formation is discussed. This is the analog of the Griffiths
temperature, but for the case of two competing orders, producing a strong
susceptibility to external fields. Cuprates may have similar features,
compatible with the large proximity effect of the very underdoped regime.Comment: 4 pages, 4 figure
On Pebble Automata for Data Languages with Decidable Emptiness Problem
In this paper we study a subclass of pebble automata (PA) for data languages
for which the emptiness problem is decidable. Namely, we introduce the
so-called top view weak PA. Roughly speaking, top view weak PA are weak PA
where the equality test is performed only between the data values seen by the
two most recently placed pebbles. The emptiness problem for this model is
decidable. We also show that it is robust: alternating, nondeterministic and
deterministic top view weak PA have the same recognition power. Moreover, this
model is strong enough to accept all data languages expressible in Linear
Temporal Logic with the future-time operators, augmented with one register
freeze quantifier.Comment: An extended abstract of this work has been published in the
proceedings of the 34th International Symposium on Mathematical Foundations
of Computer Science (MFCS) 2009}, Springer, Lecture Notes in Computer Science
5734, pages 712-72
Altitude variation of ion composition in the midlatitude trough region - Evidence for upward plasma flow
Altitude effect on ion concentration in midlatitude trough and plasmaspher
Mirror Symmetry and Landau Ginzburg Calabi-Yau Superpotentials in F-theory Compactifications
We study Landau Ginzburg (LG) theories mirror to 2D N=2 gauged linear sigma
models on toric Calabi-Yau manifolds. We derive and solve new constraint
equations for Landau Ginzburg elliptic Calabi-Yau superpotentials, depending on
the physical data of dual linear sigma models. In Calabi-Yau threefolds case,
we consider two examples. First, we give the mirror symmetry of the canonical
line bundle over the Hirzebruch surfaces . Second, we find a special
geometry with the affine so(8) Lie algebra toric data extending the geometry of
elliptically fibered K3. This geometry leads to a pure N=1 six dimensional
SO(8) gauge model from the F-theory compactification. For Calabi-Yau fourfolds,
we give a new algebraic realization for ADE hypersurfaces.Comment: 27 pages, latex. To appear in Journal of Physics A: Mathematical and
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