519 research outputs found
On the Composition of Gauge Structures
A formulation for a non-trivial composition of two classical gauge structures
is given: Two parent gauge structures of a common base space are synthesized so
as to obtain a daughter structure which is fundamental by itself. The model is
based on a pair of related connections that take their values in the product
space of the corresponding Lie algebras. The curvature, the covariant exterior
derivatives and the associated structural identities, all get contributions
from both gauge groups. The various induced structures are classified into
those whose composition is given just by trivial means, and those which possess
an irreducible nature. The pure irreducible piece, in particular, generates a
complete super-space of ghosts with an attendant set of super-BRST variation
laws, both of which are purely of a geometrical origin.Comment: Few elaborations are added to section 4 and section 5. To be
published in Journal of Physics A: Mathematical and General. 21 page
Anomalous proximity effect in gold coated (110) films: Penetration of the Andreev bound states
Scanning tunneling spectroscopy of (110) bi-layers
reveal a proximity effect markedly different from the conventional one. While
proximity-induced mini-gaps rarely appear in the Au layer, the Andreev bound
states clearly penetrate into the metal. Zero bias conductance peaks are
measured on Au layers thinner than 7 nm with magnitude similar to those
detected on the bare superconductor films. The peaks then decay abruptly with
Au thickness and disappear above 10 nm. This length is shorter than the normal
coherence length and corresponds to the (ballistic) mean free path.Comment: 5 prl format pages, 4 figures, to be published in PR
A quest for frustration driven distortion in Y2Mo2O7
We investigated the nature of the freezing in the geometrically frustrated
Heisenberg spin-glass Y2Mo2O7 by measuring the temperature dependence of the
static internal magnetic field distribution above the spin-glass temperature,
Tg, using the muSR technique. The evolution of the field distribution cannot be
explained by changes in the spin susceptibility alone and suggests a lattice
deformation. This possibility is addressed by numerical simulations of the
Heisenberg Hamiltonian with magneto-elastic coupling at T>0.Comment: 5 pages 4 figures. Accepted for publication in PR
Scanning tunneling spectroscopy characterization of the pseudogap and the x = 1/8 anomaly in La2-xSrxCuO4 thin films
Using scanning tunneling spectroscopy we examined the local density of states
of thin c-axis La2-xSrxCuO4 films, over wide doping and temperature ranges. We
found that the pseudogap exists only at doping levels lower than optimal. For x
= 0.12, close to the 'anomalous' x = 1/8 doping level, a zero bias conductance
peak was the dominant spectral feature, instead of the excepted V- shaped
(c-axis tunneling) gap structure. We have established that this surprising
effect cannot be explained by tunneling into (110) facets. Possible origins for
this unique behavior are discussed.Comment: 15 pages, 6 figure
Machine Learning-Derived Entanglement Witnesses
In this work, we show a correspondence between linear support vector machines
(SVMs) and entanglement witnesses, and use this correspondence to generate
entanglement witnesses for bipartite and tripartite qubit (and qudit) target
entangled states. An SVM allows for the construction of a hyperplane that
clearly delineates between separable states and the target entangled state;
this hyperplane is a weighted sum of observables (`features') whose
coefficients are optimized during the training of the SVM. In contrast to other
methods such as deep neural networks, the training of an SVM is a convex
optimization problem and always yields an `optimal' solution. We demonstrate
with this method the ability to obtain witnesses that require only local
measurements even when the target state is a non-stabilizer state. Furthermore,
we show that SVMs are flexible enough to allow us to rank features, and to
reduce the number of features systematically while bounding the inference
error. This programmatic approach will allow us to streamline the detection of
entangled states in experiment.Comment: 6 page
The Herbertsmithite Hamiltonian: SR measurements on single crystals
We present transverse field muon spin rotation/relaxation measurements on
single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find
that the spins are more easily polarized when the field is perpendicular to the
kagome plane. We demonstrate that the difference in magnetization between the
different directions cannot be accounted for by Dzyaloshinksii-Moriya type
interactions alone, and that anisotropic axial interaction is present.Comment: 8 pages, 3 figures, accepted to JPCM special issue on geometrically
frustrated magnetis
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