5,980 research outputs found
Observation of thermally activated glassiness and memory dip in a-NbSi insulating thin films
We present electrical conductance measurements on amorphous NbSi insulating
thin films. These films display out-of equilibrium electronic features that are
markedly different from what has been reported so far in disordered insulators.
Like in the most studied systems (indium oxide and granular Al films), a slow
relaxation of the conductance is observed after a quench to liquid helium
temperature which gives rise to the growth of a memory dip in MOSFET devices.
But unlike in these systems, this memory dip and the related conductance
relaxations are still visible up to room temperature, with clear signatures of
a temperature dependent dynamics
Quantum plasmonics: second-order coherence of surface plasmons launched by quantum emitters into a metallic film
We address the issue of the second-order coherence of single surface plasmons
launched by a quantum source of light into extended gold films. The quantum
source of light is made of a scanning fluorescent nanodiamond hosting five
nitrogen-vacancy (NV) color centers. By using a specially designed microscopy
that combines near-field optics with far-field leakage-radiation microscopy in
the Fourier space and adapted spatial filtering, we find that the quantum
statistics of the initial source of light is preserved after conversion to
surface plasmons and propagation along the polycrystalline gold film.Comment: Second version with minor changes made to comply with Referees'
comments. Editorially approved for publication in Phys. Rev. B on 22 June
201
Strong and weak semiclassical limits for some rough Hamiltonians
We present several results concerning the semiclassical limit of the time
dependent Schr\"odinger equation with potentials whose regularity doesn't
guarantee the uniqueness of the underlying classical flow. Different topologies
for the limit are considered and the situation where two bicharateristics can
be obtained out of the same initial point is emphasized
Supersymmetrization of horizontality condition: nilpotent symmetries for a free spinning relativistic particle
We derive the off-shell nilpotent and absolutely anticommuting
Becchi-Rouet-Stora-Tyutin (BRST) and anti-BRST symmetry transformations for a
supersymmetric system of a free spinning relativistic particle within the
framework of superfield approach to BRST formalism. A novel feature of our
present investigation is the consistent and clear supersymmetric modification
of the celebrated horizontality condition for the precise determination of the
proper (anti-)BRST symmetry transformations for all the bosonic and fermionic
dynamical variables of our theory which is considered on a (1, 2)-dimensional
supermanifold parameterized by an even (bosonic) variable (\tau) and a pair of
odd (fermionic) variables \theta and \bar\theta (with \theta^2 = \bar\theta^2 =
0,\; \theta \bar\theta + \bar\theta \theta = 0) of the Grassmann algebra. One
of the most important features of our present investigation is the derivation
of (anti-)BRST invariant Curci-Ferrari type restriction which turns out to be
responsible for the absolute anticommutativity of the (anti-)BRST symmetry
transformations and existence of the coupled (but equivalent) Lagrangians for
the present theory of a supersymmetric system.Comment: LaTeX file, 24 pages, version to appear in EPJ
Non-Abelian gauge field theory in scale relativity
Gauge field theory is developed in the framework of scale relativity. In this
theory, space-time is described as a non-differentiable continuum, which
implies it is fractal, i.e., explicitly dependent on internal scale variables.
Owing to the principle of relativity that has been extended to scales, these
scale variables can themselves become functions of the space-time coordinates.
Therefore, a coupling is expected between displacements in the fractal
space-time and the transformations of these scale variables. In previous works,
an Abelian gauge theory (electromagnetism) has been derived as a consequence of
this coupling for global dilations and/or contractions. We consider here more
general transformations of the scale variables by taking into account separate
dilations for each of them, which yield non-Abelian gauge theories. We identify
these transformations with the usual gauge transformations. The gauge fields
naturally appear as a new geometric contribution to the total variation of the
action involving these scale variables, while the gauge charges emerge as the
generators of the scale transformation group. A generalized action is
identified with the scale-relativistic invariant. The gauge charges are the
conservative quantities, conjugates of the scale variables through the action,
which find their origin in the symmetries of the ``scale-space''. We thus found
in a geometric way and recover the expression for the covariant derivative of
gauge theory. Adding the requirement that under the scale transformations the
fermion multiplets and the boson fields transform such that the derived
Lagrangian remains invariant, we obtain gauge theories as a consequence of
scale symmetries issued from a geometric space-time description.Comment: 24 pages, LaTe
Pressure effects on the magnetic structure in La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites
The effect of high pressure (0 - 8 GPa) on the magnetic structure of
polycrystalline samples of La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites at
5 K is investigated using neutron diffraction technique. Application of
pressure is found to modify the previously reported magnetic structure,
observed under ambient conditions, in these compounds [I. Dhiman et al., Phys.
Rev. B 77, 094440 (2008)]. In x = 0.1 composition, at 4.6(2) GPa and beyond,
A-type antiferromagnetic structure is found to coexist with CE-type
antiferromagnetic phase, observed at ambient pressure, with TN ~ 150 K. For x =
0.3 sample, as a function of pressure the CE-type phase is fully suppressed at
2.3(1) GPa and A-type antiferromagnetic phase is favored. Further Sr doping at
x = 0.4, the A-type antiferromagnetic phase is observed at ambient pressure and
for T < TN (~ 250K). This phase is retained in the studied pressure range.
However, the magnetic moment progressively reduces with increasing pressure,
indicating the suppression of A-type antiferromagnetic phase. The present study
brings out the fragile nature of the CE-type antiferromagnetic state in half
doped manganites as a function of pressure and disorder \sigma 2. We observe
that pressure required for destabilizing the CE-type antiferromagnetic state is
reduced with increasing disorder \sigma 2. External pressure and changing
A-site ionic radii have analogous effect on the magnetic structure.Comment: 9 pages, 6 figures, 1 table, To appear in Physical Review
Temperature-induced crossovers in the static roughness of a one-dimensional interface
At finite temperature and in presence of disorder, a one-dimensional elastic
interface displays different scaling regimes at small and large lengthscales.
Using a replica approach and a Gaussian Variational Method (GVM), we explore
the consequences of a finite interface width on the small-lengthscale
fluctuations. We compute analytically the static roughness of the
interface as a function of the distance between two points on the
interface. We focus on the case of short-range elasticity and random-bond
disorder. We show that for a finite width two temperature regimes exist.
At low temperature, the expected thermal and random-manifold regimes,
respectively for small and large scales, connect via an intermediate `modified'
Larkin regime, that we determine. This regime ends at a temperature-independent
characteristic `Larkin' length. Above a certain `critical' temperature that we
identify, this intermediate regime disappears. The thermal and random-manifold
regimes connect at a single crossover lengthscale, that we compute. This is
also the expected behavior for zero width. Using a directed polymer
description, we also study via a second GVM procedure and generic scaling
arguments, a modified toy model that provides further insights on this
crossover. We discuss the relevance of the two GVM procedures for the roughness
at large lengthscale in those regimes. In particular we analyze the scaling of
the temperature-dependent prefactor in the roughness B(r)\sim T^{2
\text{\thorn}} r^{2 \zeta} and its corresponding exponent \text{\thorn}. We
briefly discuss the consequences of those results for the quasistatic creep law
of a driven interface, in connection with previous experimental and numerical
studies
Yang-Mills gauge anomalies in the presence of gravity with torsion
The BRST transformations for the Yang-Mills gauge fields in the presence of
gravity with torsion are discussed by using the so-called Maurer-Cartan
horizontality conditions. With the help of an operator \d which allows to
decompose the exterior spacetime derivative as a BRST commutator we solve the
Wess-Zumino consistency condition corresponding to invariant Chern-Simons terms
and gauge anomalies.Comment: 24 pages, report REF. TUW 94-1
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