511 research outputs found
Sum rule for transport in a Luttinger liquid with long range interaction in the presence of an impurity
We show that the non-linear dc transport in a Luttinger liquid with
interaction of finite range in the presence of an impurity is governed by a sum
rule which causes the charging energy to vanish.Comment: 5 pages, RevTeX, 1 figure, to be published in Europhysics Letter
A pure-carbon ring transistor: The role of topology and structure
We report results on the rectification properties of a carbon nanotube (CNT)
ring transistor, contacted by CNT leads, whose novel features have been
recently communicated by Watanabe et al. [Appl. Phys. Lett. 78, 2928 (2001)].
This paper contains results which are validated by the experimental
observations. Moreover, we report on additional features of the transmission of
this ring device which are associated with the possibility of breaking the lead
inversion symmetry. The linear conductance displays a "chessboard"-like
behavior alternated with anomalous zero-lines which should be directly
observable in experiments. We are also able to discriminate in our results
structural properties (quasi-onedimensional confinement) from pure topological
effects (ring configuration), thus helping to gain physical intuition on the
rich ring phenomenology.Comment: 3 pages, 4 figure
Transport through a one-dimensional quantum dot
We examine the effects of long-range interactions in a quantum wire with two
impurities. We employ the bosonization technique and derive an effective action
for the system. The effect of the long-range interaction on the charging energy
and spectral properties of the island formed by the impurities and the linear
transport is discussed.Comment: 7 pages, 2 figure
Vibrational Instabilities in Resonant Electron Transport through Single-Molecule Junctions
We analyze various limits of vibrationally coupled resonant electron
transport in single-molecule junctions. Based on a master equation approach, we
discuss analytic and numerical results for junctions under a high bias voltage
or weak electronic-vibrational coupling. It is shown that in these limits the
vibrational excitation of the molecular bridge increases indefinitely, i.e. the
junction exhibits a vibrational instability. Moreover, our analysis provides
analytic results for the vibrational distribution function and reveals that
these vibrational instabilities are related to electron-hole pair creation
processes.Comment: 19 pages, 3 figure
Disorder and dephasing effect on electron transport through conjugated molecular wires in molecular junctions
Understanding electron transport processes in molecular wires connected
between contacts is a central focus in the field of molecular electronics.
Especially, the dephasing effect causing tunneling-to-hopping transition has
great importance from both applicational and fundamental points of view. We
analyzed coherent and incoherent electron transmission through conjugated
molecular wires by means of density-functional tight-binding theory within the
D'Amato-Pastawski model. Our approach can study explicitly the
structure/transport relationship in molecular junctions in a dephasing
environmental condition using only single dephasing parameter. We investigated
the length dependence and the influence of thermal fluctuations on transport
and reproduced the well-known tunneling-to-hopping transition. This approach
will be a powerful tool for the interpretation of recent conductance
measurements of molecular wires.Comment: 6 pages, 7 figures, accepted for publication in Phys. Rev.
Electrical transport through a mechanically gated molecular wire
A surface-adsorbed molecule is contacted with the tip of a scanning tunneling
microscope (STM) at a pre-defined atom. On tip retraction, the molecule is
peeled off the surface. During this experiment, a two-dimensional differential
conductance map is measured on the plane spanned by the bias voltage and the
tip-surface distance. The conductance map demonstrates that tip retraction
leads to mechanical gating of the molecular wire in the STM junction. The
experiments are compared with a detailed ab initio simulation. We find that
density functional theory (DFT) in the local density approximation (LDA)
describes the tip-molecule contact formation and the geometry of the molecular
junction throughout the peeling process with predictive power. However, a
DFT-LDA-based transport simulation following the non-equilibrium Green's
functions (NEGF) formalism fails to describe the behavior of the differential
conductance as found in experiment. Further analysis reveals that this failure
is due to the mean-field description of electron correlation in the local
density approximation. The results presented here are expected to be of general
validity and show that, for a wide range of common wire configurations,
simulations which go beyond the mean-field level are required to accurately
describe current conduction through molecules. Finally, the results of the
present study illustrate that well-controlled experiments and concurrent ab
initio transport simulations that systematically sample a large configuration
space of molecule-electrode couplings allow the unambiguous identification of
correlation signatures in experiment.Comment: 31 pages, 10 figure
L’incerto bilanciamento tra esigenze processuali, diritti dell’imputato e libertà di cronaca: a proposito della sentenza Bédat c. Svizzera (Corte EDU, Grande Camera, 29 marzo 2016)
The contribution addresses the ECtHR's decision in B\ue9dat v. Switzerland, in which the Court intervenes on the thorny issue of the balance between freedom of information and the needs of justice's administration. On one side the Court confirms the role of the presumption of innocence and the right to private life; on the other it raises several questions and some concerns about the uncertainty of the keyconcepts used (public interest and responsible press). Moreover the Court addresses critically the trend of overlapping different aspects, namely the guarantees of the fair trial and the rights relating to personality
Analytical calculation of the excess current in the OTBK theory
We present an analytical derivation of the excess current in Josephson
junctions within the Octavio-Tinkham-Blonder-Klapwijk theory for both symmetric
and asymmetric barrier strengths. We confirm the result found numerically by
Flensberg et al. for equal barriers [Phys. Rev. B 38, 8707 (1988)], including
the prediction of negative excess current for low transparencies, and we
generalize it for differing barriers. Our analytical formulae provide for
convenient fitting of experimental data, also in the less studied, but
practically relevant case of the barrier asymmetry.Comment: 13 pages, 3 figures, submitted to Superconductor Science and
Technolog
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