81 research outputs found
Non-equilibrium inelastic electronic transport: Polarization effects and vertex corrections to the self-consistent Born approximation
We study the effect of electron-vibron interactions on the inelastic
transport properties of single-molecule nanojunctions. We use the
non-equilibrium Green's functions technique and a model Hamiltonian to
calculate the effects of second-order diagrams (double-exchange DX and
dressed-phonon DPH diagrams) on the electron-vibration interaction and consider
their effects across the full range of parameter space. The DX diagram,
corresponding to a vertex correction, introduces an effective dynamical
renormalization of the electron-vibron coupling in both the purely inelastic
and the inelastic-resonant features of the IETS. The purely inelastic features
correspond to an applied bias around the energy of a vibron, while the
inelastic-resonant features correspond to peaks (resonance) in the conductance.
The DPH diagram affects only the inelastic resonant features. We also discuss
the circumstances in which the second-order diagrams may be approximated in the
study of more complex model systems.Comment: To be published in PR
Nonequilibrium effects due to charge fluctuations in intrinsic Josephson systems
Nonequilibrium effects in layered superconductors forming a stack of
intrinsic Josephson junctions are investigated. We discuss two basic
nonequilibrium effects caused by charge fluctuations on the superconducting
layers: a) the shift of the chemical potential of the condensate and b) charge
imbalance of quasi-particles, and study their influence on IV-curves and the
position of Shapiro steps.Comment: 17 pages, 2 figures, revised version slightly shortene
Charge-imbalance effects in intrinsic Josephson systems
We report on two types of experiments with intrinsic Josephson systems made
from layered superconductors which show clear evidence of nonequilibrium
effects: 1. In 2-point measurements of IV-curves in the presence of high-
frequency radiation a shift of the voltage of Shapiro steps from the canonical
value hf/(2e) has been observed. 2. In the IV-curves of double-mesa structures
an influence of the current through one mesa on the voltage measured on the
other mesa is detected. Both effects can be explained by charge-imbalance on
the superconducting layers produced by the quasi-particle current, and can be
described successfully by a recently developed theory of nonequilibrium effects
in intrinsic Josephson systems.Comment: 8pages, 9figures, submitted to Phys. Rev.
Charge-memory effect in a polaron model: equation-of-motion method for Green functions
We analyze a single-level quantum system placed between metallic leads and
strongly coupled to a localized vibrational mode, which models a singlemolecule
junction or an STM setup. We consider a polaron model describing the
interaction between electronic and vibronic degrees of freedom and develop and
examine different truncation schemes in the equation-of-motion method within
the framework of non-equilibrium Green functions. We show that upon applying
gate or bias voltage, it is possible to observe charge-bistability and
hysteretic behavior which can be the basis of a charge-memory element. We
further perform a systematic analysis of the bistability behaviour of the
system for different internal parameters such as the electron-vibron and the
lead-molecule coupling strength.Comment: 12 pages, 5 figure
Dynamics and transformations of Josephson vortex lattice in layered superconductors
We consider dynamics of Josephson vortex lattice in layered superconductors
with magnetic, charge (electrostatic) and charge-imbalance (quasiparticle)
interactions between interlayer Josephson junctions taken into account. The
macroscopic dynamical equations for interlayer Josephson phase differences,
intralayer charge and electron-hole imbalance are obtained and used for
numerical simulations. Different transformations of the vortex lattice
structure are observed. It is shown that the additional dissipation due to the
charge imbalance relaxation leads to the stability of triangular lattice.Comment: 9 pages, 3 eps figures, to be published in Phys. Rev.
Carbon Nanotube Quantum Dots with Nb Contacts
We report on the preparation of carbon nanotube quantum dots using
superconducting electrodes made of niobium. Gate-controllable supercurrents
with values of up to 30 nA are induced by the proximity effect. The IV-curves
are hysteretic at low temperature and the corresponding switching histograms
have a width of ~0.5-2. An on-chip resistive environment integrated in the
sample layout is used in order to increase the switching current.Comment: 7 pages, 3 figure
The c-axis charge traveling wave in coupled system of Josephson junctions
We demonstrate a manifestation of the charge traveling wave along the c-axis
(TW) in current voltage characteristics of coupled Josephson junctions in
high- superconductors. The branches related to the TW with different
wavelengths are found for the stacks with different number of Josephson
junctions at different values of system's parameters. Transitions between the
TW branches and the outermost branch are observed. Time dependence of the
electric charge in the superconducting layers and charge-charge correlation
functions for TW and outermost branches show different behavior with bias
current. We propose an experimental testing of the TW by microwave irradiation.Comment: Supplement : http://theor.jinr.ru/~hamdipur/lambda0.av
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