393 research outputs found
Role of heating and current-induced forces in the stability of atomic wires
We investigate the role of local heating and forces on ions in the stability
of current-carrying aluminum wires. We find that heating increases with wire
length due to a red shift of the frequency spectrum. Nevertheless, the local
temperature of the wire is relatively low for a wide range of biases provided
good thermal contact exists between the wire and the bulk electrodes. On the
contrary, current-induced forces increase substantially as a function of bias
and reach bond-breaking values at about 1 V. These results suggest that local
heating promotes low-bias instabilities if dissipation into the bulk electrodes
is not efficient, while current-induced forces are mainly responsible for the
wire break-up at large biases. We compare these results to experimental
observations.Comment: 4 pages, 4 figure
Topological jamming of spontaneously knotted polyelectrolyte chains driven through a nanopore
The advent of solid state nanodevices allows for interrogating the
physico-chemical properties of a polyelectrolyte chain by electrophoretically
driving it through a nanopore. Salient dynamical aspects of the translocation
process have been recently characterized by theoretical and computational
studies of model polymer chains free from self-entanglement. However,
sufficiently long equilibrated chains are necessarily knotted. The impact of
such topological "defects" on the translocation process is largely unexplored,
and is addressed in this study. By using Brownian dynamics simulations on a
coarse-grained polyelectrolyte model we show that knots, despite being trapped
at the pore entrance, do not "per se" cause the translocation process to jam.
Rather, knots introduce an effective friction that increases with the applied
force, and practically halts the translocation above a threshold force. The
predicted dynamical crossover, which is experimentally verifiable, is of
relevance in applicative contexts, such as DNA nanopore sequencing.Comment: 6 pages; 7 figure
Heterovalent interlayers and interface states: an ab initio study of GaAs/Si/GaAs (110) and (100) heterostructures
We have investigated ab initio the existence of localized states and
resonances in abrupt GaAs/Si/GaAs (110)- and (100)-oriented heterostructures
incorporating 1 or 2 monolayers (MLs) of Si, as well as in the fully developed
Si/GaAs (110) heterojunction. In (100)-oriented structures, we find both
valence- and conduction-band related near-band edge states localized at the
Si/GaAs interface. In the (110) systems, instead, interface states occur deeper
in the valence band; the highest valence-related resonances being about 1 eV
below the GaAs valence-band maximum. Using their characteristic bonding
properties and atomic character, we are able to follow the evolution of the
localized states and resonances from the fully developed Si/GaAs binary
junction to the ternary GaAs/Si/GaAs (110) systems incorporating 2 or 1 ML of
Si. This approach also allows us to show the link between the interface states
of the (110) and (100) systems. Finally, the conditions for the existence of
localized states at the Si/GaAs (110) interface are discussed based on a
Koster-Slater model developed for the interface-state problem.Comment: REVTeX 4, 14 pages, 15 EPS figure
Critical branching processes in digital memcomputing machines
Memcomputing is a novel computing paradigm that employs time non-locality
(memory) to solve combinatorial optimization problems. It can be realized in
practice by means of non-linear dynamical systems whose point attractors
represent the solutions of the original problem. It has been previously shown
that during the solution search digital memcomputing machines go through a
transient phase of avalanches (instantons) that promote dynamical long-range
order. By employing mean-field arguments we predict that the distribution of
the avalanche sizes follows a Borel distribution typical of critical branching
processes with exponent . We corroborate this analysis by solving
various random 3-SAT instances of the Boolean satisfiability problem. The
numerical results indicate a power-law distribution with exponent , in very good agreement with the mean-field analysis. This indicates
that memcomputing machines self-tune to a critical state in which avalanches
are characterized by a branching process, and that this state persists across
the majority of their evolution.Comment: 5 pages, 3 figure
Effect of electron-phonon scattering on shot noise in nanoscale junctions
We investigate the effect of electron-phonon inelastic scattering on shot
noise in nanoscale junctions in the regime of quasi-ballistic transport. We
predict that when the local temperature of the junction is larger than its
lowest vibrational mode energy , the inelastic contribution to shot noise
(conductance) increases (decreases) with bias as (). The
corresponding Fano factor thus increases as . We also show that the
inelastic contribution to the Fano factor saturates with increasing thermal
current exchanged between the junction and the bulk electrodes to a value
which, for , is independent of bias. A measurement of shot noise may
thus provide information about the local temperature and heat dissipation in
nanoscale conductors.Comment: 4 pages, 2 figure
Single-particle and Interaction Effects on the Cohesion and Transport and Magnetic Properties of Metal Nanowires at Finite Voltages
The single-particle and interaction effects on the cohesion, electronic
transport, and some magnetic properties of metallic nanocylinders have been
studied at finite voltages by using a generalized mean-field electron model.
The electron-electron interactions are treated in the self-consistent Hartree
approximation. Our results show the single-particle effect is dominant in the
cohesive force, while the nonzero magnetoconductance and magnetotension
coefficients are attributed to the interaction effect. Both single-particle and
interaction effects are important to the differential conductance and magnetic
susceptibility.Comment: 5 pages, 6 figure
Electronic structure of the Au/benzene-1,4-dithiol/Au transport interface: Effects of chemical bonding
We present results of electronic structure calculations for well-relaxed
Au/benzene-1,4-dithiol/Au molecular contacts, based on density functional
theory and the generalized gradient approximation. Electronic states in the
vicinity of the Fermi energy are mainly of Au 5d and S 3p symmetry, whereas
contributions of C 2p states are very small. Hybridization between C 2p
orbitals within the benzene substructure is strongly suppressed due to S-C
bonding. In agreement with experimental findings, this corresponds to a
significantly reduced conductance of the molecular contact.Comment: 7 pages, 5 figures, accepted by Chemical Physics Letter
Reconstructing Fourier's law from disorder in quantum wires
The theory of open quantum systems is used to study the local temperature and
heat currents in metallic nanowires connected to leads at different
temperatures. We show that for ballistic wires the local temperature is almost
uniform along the wire and Fourier's law is invalid. By gradually increasing
disorder, a uniform temperature gradient ensues inside the wire and the thermal
current linearly relates to this local temperature gradient, in agreement with
Fourier's law. Finally, we demonstrate that while disorder is responsible for
the onset of Fourier's law, the non-equilibrium energy distribution function is
determined solely by the heat baths
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