479 research outputs found
Anomalous Conductance Distribution in Quasi-One Dimension: Possible Violation of One-Parameter Scaling Hypothesis
We report measurements of conductance distribution in a set of
quasi-one-dimensional gold wires. The distribution includes the second cumulant
or the variance which describes the universal conductance fluctuations, and the
third cumulant which denotes the leading deviation. We have observed an
asymmetric contribution--or, a nonvanishing third cumulant--contrary to the
expectation for quasi-one-dimensional systems in the noninteracting theories in
the one-parameter scaling framework, which include the perturbative
diagrammatic calculations and the random matrix theory.Comment: 5 PAGE
Deviations from the Gaussian distribution of mesoscopic conductance fluctuations
The conductance distribution of metallic mesoscopic systems is considered.
The variance of this distribution describes the universal conductance
fluctuations, yielding a Gaussian distribution of the conductance. We calculate
diagrammatically the third cumulant of this distribution, the leading deviation
from the Gaussian. We confirm random matrix theory calculations that the
leading contribution in quasi-one dimension vanishes. However, in quasi two
dimensions the third cumulant is negative, whereas in three dimensions it is
positive.Comment: 9 pages, Revtex, with eps figures,to appear in Phys Rev
Evaluational adjectives
This paper demarcates a theoretically interesting class of "evaluational adjectives." This class includes predicates expressing various kinds of normative and epistemic evaluation, such as predicates of personal taste, aesthetic adjectives, moral adjectives, and epistemic adjectives, among others. Evaluational adjectives are distinguished, empirically, in exhibiting phenomena such as discourse-oriented use, felicitous embedding under the attitude verb `find', and sorites-susceptibility in the comparative form. A unified degree-based semantics is developed: What distinguishes evaluational adjectives, semantically, is that they denote context-dependent measure functions ("evaluational perspectives")—context-dependent mappings to degrees of taste, beauty, probability, etc., depending on the adjective. This perspective-sensitivity characterizing the class of evaluational adjectives cannot be assimilated to vagueness, sensitivity to an experiencer argument, or multidimensionality; and it cannot be demarcated in terms of pretheoretic notions of subjectivity, common in the literature. I propose that certain diagnostics for "subjective" expressions be analyzed instead in terms of a precisely specified kind of discourse-oriented use of context-sensitive language. I close by applying the account to `find x PRED' ascriptions
Observation of individual molecules trapped on a nanostructured insulator
For the first time, ordered polar molecules confined in monolayer-deep
rectangular pits produced on an alkali halide surface by electron irradiation
have been resolved at room temperature by non-contact atomic force microscopy.
Molecules self-assemble in a specific fashion inside pits of width smaller than
15 nm. By contrast no ordered aggregates of molecules are observed on flat
terraces. Conclusions regarding nucleation and ordering mechanisms are drawn.
Trapping in pits as small as 2 nm opens a route to address single molecules
Universal Conductance Distributions in the Crossover between Diffusive and Localization Regimes
The full distribution of the conductance in quasi-one-dimensional
wires with rough surfaces is analyzed from the diffusive to the localization
regime. In the crossover region, where the statistics is dominated by only one
or two eigenchannels, the numerically obtained P(G) is found to be independent
of the details of the system with the average conductance as the only
scaling parameter. For < e^2/h, P(G) is given by an essentially
``one-sided'' log-normal distribution. In contrast, for e^2/h <= 2e^2/h,
the shape of P(G) remarkable agrees with those predicted by random matrix
theory for two fluctuating transmission eigenchannels.Comment: Accepted for publication in Phys. Rev. Let
Intensity correlations in electronic wave propagation in a disordered medium: the influence of spin-orbit scattering
We obtain explicit expressions for the correlation functions of transmission
and reflection coefficients of coherent electronic waves propagating through a
disordered quasi-one-dimensional medium with purely elastic diffusive
scattering in the presence of spin-orbit interactions. We find in the metallic
regime both large local intensity fluctuations and long-range correlations
which ultimately lead to universal conductance fluctuations. We show that the
main effect of spin-orbit scattering is to suppress both local and long-range
intensity fluctuations by a universal symmetry factor 4. We use a scattering
approach based on random transfer matrices.Comment: 15 pages, written in plain TeX, Preprint OUTP-93-42S (University of
Oxford), to appear in Phys. Rev.
"Optical conductance fluctuations: diagrammatic analysis in Landauer approach and non-universal effects"
The optical conductance of a multiple scattering medium is the total
transmitted light of a diffuse incoming beam. This quantity, very analogous to
the electronic conductance, exhibits universal conductance fluctuations. We
perform a detailed diagrammatic analysis of these fluctuations. With a
Kadanoff-Baym technique all the leading diagrams are systematically generated.
A cancellation of the short distance divergencies occurs, that yields a well
behaved theory. The analytical form of the fluctuations is calculated and
applied to optical systems. Absorption and internal reflections reduce the
fluctuations significantly.Comment: 25 pages Revtex 3.0, 18 seperate postscript figure
Spectroscopic investigation of the deeply buried Cu In,Ga S,Se 2 Mo interface in thin film solar cells
The Cu In,Ga S,Se 2 Mo interface in thin film solar cells has been investigated by surface sensitive photoelectron spectroscopy, bulk sensitive X ray emission spectroscopy, and atomic force microscopy. It is possible to access this deeply buried interface by using a suitable lift off technique, which allows to investigate the back side of the absorber layer as well as the front side of the Mo back contact. We find a layer of Mo S,Se 2 on the surface of the Mo back contact and a copper poor stoichiometry at the back side of the Cu In,Ga S,Se 2 absorber. Furthermore, we observe that the Na content at the Cu In,Ga S,Se 2 Mo interface as well as at the inner grain boundaries in the back contact region is significantly lower than at the absorber front surfac
Classical Monopoles: Newton, NUT-space, gravomagnetic lensing and atomic spectra
Stimulated by a scholium in Newton's Principia we find some beautiful results
in classical mechanics which can be interpreted in terms of the orbits in the
field of a mass endowed with a gravomagnetic monopole. All the orbits lie on
cones! When the cones are slit open and flattened the orbits are exactly the
ellipses and hyperbolae that one would have obtained without the gravomagnetic
monopole.
The beauty and simplicity of these results has led us to explore the similar
problems in Atomic Physics when the nuclei have an added Dirac magnetic
monopole. These problems have been explored by others and we sketch the
derivations and give details of the predicted spectrum of monopolar hydrogen.
Finally we return to gravomagnetic monopoles in general relativity. We
explain why NUT space has a non-spherical metric although NUT space itself is
the spherical space-time of a mass with a gravomagnetic monopole. We
demonstrate that all geodesics in NUT space lie on cones and use this result to
study the gravitational lensing by bodies with gravomagnetic monopoles.
We remark that just as electromagnetism would have to be extended beyond
Maxwell's equations to allow for magnetic monopoles and their currents so
general relativity would have to be extended to allow torsion for general
distributions of gravomagnetic monopoles and their currents. Of course if
monopoles were never discovered then it would be a triumph for both Maxwellian
Electromagnetism and General Relativity as they stand!Comment: 39 pages, 9 figures and 2 tables available on request from the
author
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