442 research outputs found
Huge negative differential conductance in Au-H2 molecular nanojunctions
Experimental results showing huge negative differential conductance in
gold-hydrogen molecular nanojunctions are presented. The results are analyzed
in terms of two-level system (TLS) models: it is shown that a simple TLS model
cannot produce peaklike structures in the differential conductance curves,
whereas an asymmetrically coupled TLS model gives perfect fit to the data. Our
analysis implies that the excitation of a bound molecule to a large number of
energetically similar loosely bound states is responsible for the peaklike
structures. Recent experimental studies showing related features are discussed
within the framework of our model.Comment: 9 pages, 8 figure
The effect of dynamical Bloch oscillations on optical-field-induced current in a wide gap dielectric
We consider the motion of charge carriers in a bulk wide-gap dielectric
interacting with a few-cycle laser pulse. A semiclassical model based on Bloch
equations is applied to describe the emerging time-dependent macroscopic
currents for laser intensities approaching the damage threshold. At such laser
intensities, electrons can reach edges of the first Brillouin zone even for
electron-phonon scattering rates as high as those known for SiO_2. We find
that, whenever this happens, Brag-like reflections of electron waves, also
known as Bloch oscillations, affect the dependence of the charge displaced by
the laser pulse on its carrier-envelope phase.Comment: This version corrects a mistake in the paper published by the New
Journal of Physics: panel (a) of Fig. 9 depicts -s(t_0=0) rather than
s(t_0=0
Conductance of Pd-H nanojunctions
Results of an experimental study of palladium nanojunctions in hydrogen
environment are presented. Two new hydrogen-related atomic configurations are
found, which have a conductances of ~0.5 and ~1 quantum unit (2e^2/h). Phonon
spectrum measurements demonstrate that these configurations are situated
between electrodes containing dissolved hydrogen. The crucial differences
compared to the previously studied Pt-H_2 junctions, and the possible
microscopic realizations of the new configurations in palladium-hydrogen
atomic-sized contacts are discussed.Comment: 4 pages, 4 figure
Dynamics of periodic anticrossings: Decoherence, pointer states and hysteresis curves
We consider a strongly driven two-level (spin) system, with a periodic
external field that induces a sequence of avoided level crossings. The spin
system interacts with a bosonic reservoir which leads to decoherence. A
Markovian dynamical equation is introduced without relying on the rotating wave
approximation in the system-external field interaction. We show that the time
evolution of the two-level system is directed towards an incoherent sum of
periodic Floquet states regardless of the initial state and even the type of
the coupling to the environment. Analyzing the time scale of approaching these
time-dependent pointer states, information can be deduced concerning the nature
and strength of the system-environment coupling. The inversion as a function of
the external field is usually multi-valued, and the form of these hysteresis
curves is qualitatively different for low and high temperatures. For moderate
temperatures we found that the series of Landau-Zener-St\"{u}ckelberg-type
transitions still can be used for state preparation, regardless of the
decoherence rate. Possible applications include quantum information processing
and molecular nanomagnets.Comment: 10 pages, 9 slightly reduced quality figures, submitted to PRA; More
details concerning applications to molacular nanomagnets are give
The effect of irradiation-induced disorder on the conductivity and critical temperature of the organic superconductor -(BEDT-TTF)Cu(SCN)
We have introduced defects into clean samples of the organic superconductor
-(BEDT-TTF)Cu(SCN) in order to determine their effect on the
temperature dependence of the conductivity and the critical temperature . We find a violation of Matthiessen's rule that can be explained by a model
of the conductivity involving a defect-assisted interlayer channel which acts
in parallel with the band-like conductivity. We observe an unusual dependence
of on residual resistivity which is not consistent with the
generalised Abrikosov-Gor'kov theory for an order parameter with a single
component, providing an important constraint on models of the superconductivity
in this material
Hall effect in quasi one-dimensional organic conductors
We study the Hall effect in a system of weakly coupled Luttinger Liquid
chains, using a Memory function approach to compute the Hall constant in the
presence of umklapp scattering along the chains. In this approximation, the
Hall constant decomposes into two terms: a high-frequency term and a Memory
function term. For the case of zero umklapp scattering, where the Memory
function vanishes, the Hall constant is simply the band value, in agreement
with former results in a similar model with no dissipation along the chains.
With umklapp scattering along the chains, we find a power-law temperature
dependance of the Hall constant. We discuss the applications to quasi 1D
organic conductors at high temperatures.Comment: Proceedings of the ISCOM conference "Sixth International Symposium on
Crystalline Organic Metals, Superconductors, and Ferromagnets", Key West,
Florida, USA (Sept. 2005), to be plublished in the Journal of Low Temperature
Physic
Fermi liquid identities for the Infinite U Anderson Model
We show how the electron gas methods of Luttinger, Ward and Nozi\`eres can be
applied to the infinite U Anderson impurity model within a Schwinger boson
treatment. Working to all orders in a 1/N expansion, we show how the Friedel
Langreth relationship, the Yamada-Yosida-Yoshimori and the Shiba-Korringa
relations can be derived, under the assumption that the spinon and holon fields
are gapped. One of the remarkable features of this treatment, is that the
Landau amplitudes depend on the exchange of low energy virtual spinons and
holons. We end the paper with a discussion on the extension of our approach to
the lattice, where the spinon-holon is expected to close at a quantum critical
point.Comment: 18 pages. Version 2 revised after referees comment
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