36,869 research outputs found
High orbital-moment Cooper pairs by crystalline symmetry breaking
The pairing structure of superconducting materials is regulated by the point
group symmetries of the crystal. Here, we study spin-singlet multiorbital
superconductivity in materials with unusually low crystalline symmetry content
and unveil the the appearance of even-parity (s-wave) Cooper pairs with high
orbital moment. We show that the lack of mirror and rotation symmetries makes
pairing states with quintet orbital angular momentum symmetry-allowed. A
remarkable fingerprint of this type of pairing state is provided by a
nontrivial superconducting phase texture in momentum space with -shifted
domains and walls with anomalous phase winding. The pattern of the quintet
pairing texture is shown to depend on the orientation of the orbital
polarization and the strength of the mirror and/or rotation symmetry breaking
terms. Such momentum dependent phase makes Cooper pairs with net orbital
component suited to design orbitronic Josephson effects. We discuss how an
intrinsic orbital dependent phase can set out anomalous Josephson couplings by
employing superconducting leads with nonequivalent breaking of crystalline
symmetry.Comment: 11 pages, 9 figure
Polar Smectic Films
We report on a new experimental procedure for forming and studying polar
smectic liquid crystal films. A free standing smectic film is put in contact
with a liquid drop, so that the film has one liquid crystal/liquid interface
and one liquid crystal/air interface. This polar environment results in changes
in the textures observed in the film, including a boojum texture and a
previously unobserved spiral texture in which the winding direction of the
spiral reverses at a finite radius from its center. Some aspects of these
textures are explained by the presence of a Ksb term in the bulk elastic free
energy density that favors a combination of splay and bend deformations.Comment: 4 pages, REVTeX, 3 figures, submitted to PR
Global Precedence In Visual Search? Not So Fast: Evidence Instead For An Oblique Effect
The evidence from an earlier report of global precedence in visual search is reexamined, Two new experiments are reported. The results of the first experiment indicate that the confusability of oblique orientations (a class-2 oblique effect) rather than global precedence was responsible for the earlier results. The results of the second experiment show that the effect critically depends on the presence of heterogeneous distracters rather than on differences in raw processing speed for different spatial scales. The possible role of symmetry is discussed
Phase boundary anisotropy and its effects on the maze-to-lamellar transition in a directionally solidified Al-Al2Cu eutectic
Solid-solid phase boundary anisotropy is a key factor controlling the
selection and evolution of non-faceted eutectic patterns during directional
solidification. This is most remarkably observed during the so-called
maze-to-lamellar transition. By using serial sectioning, we followed the
spatio-temporal evolution of a maze pattern over long times in a large Al-Al2Cu
eutectic grain with known crystal orientation of the Al and Al2Cu phases, hence
known crystal orientation relationship (OR). The corresponding phase boundary
energy anisotropy (-plot) was also known, as being previously estimated
from molecular-dynamics computations. The experimental observations reveal the
time-scale of the maze-to-lamellar transition and shed light on the processes
involved in the gradual alignment of the phase boundaries to one distinct
energy minimum which nearly corresponds to one distinct plane from the family
. This particular plane is selected
due to a crystallographic bias induced by a small disorientation of the
crystals relative to the perfect OR. The symmetry of the OR is thus slightly
broken, which promotes lamellar alignment. Finally, the maze-to-lamellar
transition leaves behind a network of fault lines inherited from the phase
boundary alignment process. In the maze pattern, the fault lines align along
the corners of the Wulff shape, thus allowing us to propose a link between the
pattern defects and missing orientations in the Wulff shapeComment: 26 pages, 6 figure
Chemical order and crystallographic texture of FePd:Cu thin alloy films
FePd thin films have been recently considered as promising material for
high-density magnetic storage devices. However, it is necessary to find a
proper method of fabrication for the (001)-textured and chemically well-ordered
alloy. In this paper, we present the detailed investigations of lattice
parameters, chemical order degree, grain sizes and crystallographic texture,
carried out on FePd alloys with 10 at.% of Cu addition. The initial [Cu(0.2
nm)/Fe(0.9 nm)/Pd(1.1 nm)]x5 multilayers were thermally evaporated in an
ultra-high vacuum on MgO(100), Si(100), Si(111) and Si(100) covered by 100 nm
thick layer of amorphous SiO2. In order to obtain homogeneous FePd:Cu alloy,
the multilayers were annealed in two different ways. First, the samples were
rapidly annealed in nitrogen atmosphere at 600oC for 90 seconds. Next, the long
annealing in a high vacuum for 1 hour at 700oC was done. This paper focuses on
quantitative investigations of the chemical order degree and crystallographic
texture of ternary FePd:Cu alloys deposited on four different substrates. In
order to obtain both quantities we have taken a novel approach to consider the
problem of dopant atoms located in the FePd structure. The studies of the
structure were done using X-Ray Diffraction (XRD) performed with synchrotron
radiation and pole figures measurements. We have found that the addition of Cu
changes the FePd lattice parameters and lattice distortion. We have also shown,
that using different substrates it is possible to obtain a FePd:Cu alloy with
different chemical order and texture. Moreover, it was observed that texture
category is substrate dependent
Traditional and new principles of perceptual grouping
Perceptual grouping refers to the process of determining which regions and parts of the visual scene belong together as parts of higher order perceptual units such as objects or patterns. In the early 20th century, Gestalt psychologists identified a set of classic grouping principles which specified how some image features lead to grouping between elements given that all other factors were held constant. Modern vision scientists have expanded this list to cover a wide range of image features but have also expanded the importance of learning and other non-image factors. Unlike early Gestalt accounts which were based largely on visual demonstrations, modern theories are often explicitly quantitative and involve detailed models of how various image features modulate grouping. Work has also been done to understand the rules by which different grouping principles integrate to form a final percept. This chapter gives an overview of the classic principles, modern developments in understanding them, and new principles and the evidence for them. There is also discussion of some of the larger theoretical issues about grouping such as at what stage of visual processing it occurs and what types of neural mechanisms may implement grouping principles
Synthesizing Skyrmion Molecules in Fe-Gd Thin Films
We show that properly engineered amorphous Fe-Gd alloy thin films with
perpendicular magnetic anisotropy exhibit room-temperature skyrmion molecules,
or a pair of like-polarity, opposite-helicity skyrmions. Magnetic mirror
symmetry planes present in the stripe phase, instead of chiral exchange,
determine the internal skyrmion structure and the net achirality of the
skyrmion phase. Our study shows that stripe domain engineering in amorphous
alloy thin films may enable the creation of skyrmion phases with
technologically desirable properties.Comment: 15 pages, 6 figures. Accepted for publication in Applied Physics
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