2,291 research outputs found
Majorana Fermions and Non-Abelian Statistics in Three Dimensions
We show that three dimensional superconductors, described within a Bogoliubov
de Gennes framework can have zero energy bound states associated with pointlike
topological defects. The Majorana fermions associated with these modes have
non-Abelian exchange statistics, despite the fact that the braid group is
trivial in three dimensions. This can occur because the defects are associated
with an orientation that can undergo topologically nontrivial rotations. A new
feature of three dimensional systems is that there are "braidless" operations
in which it is possible to manipulate the groundstate associated with a set of
defects without moving or measuring them. To illustrate these effects we
analyze specific architectures involving topological insulators and
superconductors.Comment: 4 pages, 2 figures, published versio
Continuous vortex pumping into a spinor condensate with magnetic fields
We study the mechanisms and the limits of pumping vorticity into a spinor
condensate through manipulations of magnetic (B-) fields. We discover a
fundamental connection between the geometrical properties of the magnetic
fields and the quantized circulation of magnetically trapped atoms, a result
which generalizes several recent experimental and theoretical studies. The
optimal procedures are devised that are capable of continuously increasing or
decreasing a condensate's vorticity by repeating certain two step B-field
manipulation protocols. We carry out detailed numerical simulations that
support the claim that our protocols are highly efficient, stable, and robust
against small imperfections of all types. Our protocols can be implemented
experimentally within current technologies.Comment: 9 pages, 6 figure
Zero Landau level in folded graphene nanoribbons
Graphene nanoribbons can be folded into a double layer system keeping the two
layers decoupled. In the Quantum Hall regime folds behave as a new type of Hall
bar edge. We show that the symmetry properties of the zero Landau level in
metallic nanoribbons dictate that the zero energy edge states traversing a fold
are perfectly transmitted onto the opposite layer. This result is valid
irrespective of fold geometry, magnetic field strength and crystallographic
orientation of the nanoribbon. Backscattering suppression on the N=0 Hall
plateau is ultimately due to the orthogonality of forward and backward
channels, much like in the Klein paradox.Comment: Final published version, with supplementary material appendi
Imprinting the memory into paste and its visualization as crack patterns in drying process
In the drying process of paste, we can imprint into the paste the order how
it should be broken in the future. That is, if we vibrate the paste before it
is dried, it remembers the direction of the initial external vibration, and the
morphology of resultant crack patterns is determined solely by the memory of
the direction. The morphological phase diagram of crack patterns and the
rheological measurement of the paste show that this memory effect is induced by
the plasticity of paste.Comment: 4 pages, 3 figures, submitted to JPS
Synthesis of perfluoroalkylene aromatic diamines
Analogues of methylene dianilines were synthesized, in which the methylene group between the two aromatic nuclei was replaced by various perfluoroalkylene linkage. The hydrolytic thermal, and thermal oxidative stabilities of PMR Polyimides derived from these diamines were determined. Three types of PMR Polyimide discs were fabricated from the dimethyl ester of 3,3', 4,4'-benzophenonetetracarboxylic acid, the methyl ester of 5-norbornene-2,3-dicarboxylic acid, and one of the following three diamines: methyl dianiline, 1,3-bis(4-aminophenyl)hexafluoropropane, and 2,2-bis(4-aminophenyl)hexafluoropropane. The polyimide based on 2,2-bis(4-aminophenyl)hexafluoropropane exhibited the best hydrolytic, thermal, and thermal oxidative stability as determined by moisture uptake and thermogravimetric analysis
Improved perfluoroalkylether fluid development
The objective of this program was to optimize and scale up the linear perfluoroalkylether stabilization process and to provide test data regarding the fluids' thermal oxidative stability in the presence of metal alloys. The stabilization of Fomblin Z-25 was scaled up to 300 g of fluid. The modified fluid was stable at 316 C in oxygen in the presence of M-50 alloy for more than 24 hrs but less than 40 hrs; the amount of volatiles produced after 24 hrs was 5.5 mg/g. In the presence of Ti(4Al,4Mn) alloy, under the above conditions, following an exposure of 24 hrs, the amount of volatiles formed was 6.2 mg/g; 56 hrs exposure yielded 13.9 mg/g. The commercial fluid at 288 C (in oxygen) in the presence of M-50 after 15 hrs of exposure decomposed extensively, 342 mg/g; in the presence of Ti(4Al,4Mn) alloy after only 8 hrs at 288 C, the amount of volatiles was 191 mg/g. Formulation of the commercial fluid with C2PN3 additive was not as effective as the stabilization processing. All the perfluoroalkylether fluids studied were stable in nitrogen at 343 C. The thermal oxidative stability in the absence of metal alloys varied, with Aflunox exhibiting the best behavior. All the fluids were degraded in oxygen at 316 C during 24 hrs exposure to Ti(4Al,4Mn) alloy with the exception of a perfluoroalkylether substituted triazine and the modified Z-25
Effects of mechanical rotation on spin currents
We study the Pauli--Schr\"odinger equation in a uniformly rotating frame of
reference to describe a coupling of spins and mechanical rotations. The
explicit form of the spin-orbit interaction (SOI) with the inertial effects due
to the mechanical rotation is presented. We derive equations of motion for a
wavepacket of electrons in two-dimensional planes subject to the SOI. The
solution is a superposition of two cyclotron motions with different frequencies
and a circular spin current is created by the mechanical rotation.Comment: 4 pages, 2 figure
Topological Signature of First Order Phase Transitions
We show that the presence and the location of first order phase transitions
in a thermodynamic system can be deduced by the study of the topology of the
potential energy function, V(q), without introducing any thermodynamic measure.
In particular, we present the thermodynamics of an analytically solvable
mean-field model with a k-body interaction which -depending on the value of k-
displays no transition (k=1), second order (k=2) or first order (k>2) phase
transition. This rich behavior is quantitatively retrieved by the investigation
of a topological invariant, the Euler characteristic, of some submanifolds of
the configuration space. Finally, we conjecture a direct link between the Euler
characteristic and the thermodynamic entropy.Comment: 6 pages, 2 figure
Boundary Conditions in Stepwise Sine-Gordon Equation and Multi-Soliton Solutions
We study the stepwise sine-Gordon equation, in which the system parameter is
different for positive and negative values of the scalar field. By applying
appropriate boundary conditions, we derive relations between the soliton
velocities before and after collisions. We investigate the possibility of
formation of heavy soliton pairs from light ones and vise versa. The concept of
soliton gun is introduced for the first time; a light pair is produced moving
with high velocity, after the annihilation of a bound, heavy pair. We also
apply boundary conditions to static, periodic and quasi-periodic solutions.Comment: 14 pages, 8 figure
Nonclassical correlation in a multipartite quantum system: two measures and evaluation
There is a commonly recognized paradigm in which a multipartite quantum
system described by a density matrix having no product eigenbasis is considered
to possess nonclassical correlation. Supporting this paradigm, we define two
entropic measures of nonclassical correlation of a multipartite quantum system.
One is defined as the minimum uncertainty about a joint system after we collect
outcomes of particular local measurements. The other is defined by taking the
maximum over all local systems about the minimum distance between a genuine set
and a mimic set of eigenvalues of a reduced density matrix of a local system.
The latter measure is based on an artificial game to create mimic eigenvalues
of a reduced density matrix of a local system from eigenvalues of a density
matrix of a global system. Numerical computation of these measures for several
examples is performed.Comment: v1: 10 pages, 8 figures, IOPART, v2: introduction modified, figure 7
replaced, v3: 10 pages, 10 figures, RevTeX4, major revision with an
additional measure introduced, title changed (previous title: Non-classical
correlation in a multi-partite quantum system reconsidered), to appear in
Phys. Rev.
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