173 research outputs found
Jahn-Teller Distortions and the Supershell Effect in Metal Nanowires
A stability analysis of metal nanowires shows that a Jahn-Teller deformation
breaking cylindrical symmetry can be energetically favorable, leading to stable
nanowires with elliptic cross sections. The sequence of stable cylindrical and
elliptical nanowires allows for a consistent interpretation of experimental
conductance histograms for alkali metals, including both the shell and
supershell structures. It is predicted that for gold, elliptical nanowires are
even more likely to form since their eccentricity is smaller than for alkali
metals. The existence of certain metastable ``superdeformed'' nanowires is also
predicted
Electronic and atomic shell structure in aluminum nanowires
We report experiments on aluminum nanowires in ultra-high vacuum at room
temperature that reveal a periodic spectrum of exceptionally stable structures.
Two "magic" series of stable structures are observed: At low conductance, the
formation of stable nanowires is governed by electronic shell effects whereas
for larger contacts atomic packing dominates. The crossover between the two
regimes is found to be smooth. A detailed comparison of the experimental
results to a theoretical stability analysis indicates that while the main
features of the observed electron-shell structure are similar to those of
alkali and noble metals, a sequence of extremely stable wires plays a unique
role in Aluminum. This series appears isolated in conductance histograms and
can be attributed to "superdeformed" non-axisymmetric nanowires.Comment: 15 pages, 9 figure
On the Stability and Structural Dynamics of Metal Nanowires
This article presents a brief review of the nanoscale free-electron model,
which provides a continuum description of metal nanostructures. It is argued
that surface and quantum-size effects are the two dominant factors in the
energetics of metal nanowires, and that much of the phenomenology of nanowire
stability and structural dynamics can be understood based on the interplay of
these two competing factors. A linear stability analysis reveals that metal
nanocylinders with certain magic conductance values G=1, 3, 6, 12, 17, 23, 34,
42, 51, 67, 78, 96, ... times the conductance quantum are exceptionally stable.
A nonlinear dynamical simulation of nanowire structural evolution reveals a
universal equilibrium shape consisting of a magic cylinder suspended between
unduloidal contacts. The lifetimes of these metastable structures are also
computed.Comment: 8 pages, 6 figure
When words collide: Bayesian meta-analyses of distractor and target properties in the picture-word interference paradigm
In the picture-word interference paradigm, participants name pictures while
ignoring a written or spoken distractor word. Naming times to the pictures are
slowed down by the presence of the distractor word. Various properties of the
distractor modulate this slow down, for example naming times are shorter with
frequent vs. infrequent distractors. Building on this line of research, the
present study investigates in more detail the impact of distractor and target
word properties on picture naming times. We report the results of several
Bayesian meta-analyses, based on 35 datasets. The aim of the first analysis was
to obtain an estimation of the size of the distractor frequency effect, and of
its precision, in typical picture-word interference experiments where this
variable is not manipulated. The analysis shows that a one-unit increase in log
frequency results in response times to the pictures decreasing by about 4ms
(95% Credible Interval: [-6, -2]). With the second and third analyses, we show
that after accounting for the effect of frequency, two variables known to
influence processing times in visual word processing tasks also influence
picture naming times: distractor length and orthographic neighborhood. Finally,
we found that distractor word frequency and target word frequency interact; the
effect of distractor frequency decreases as the frequency of the target word
increases. We discuss the theoretical and methodological implications of these
findings, as well as the importance of obtaining high-precision estimates of
experimental effects
Stability and Symmetry Breaking in Metal Nanowires
A general linear stability analysis of simple metal nanowires is presented
using a continuum approach which correctly accounts for material-specific
surface properties and electronic quantum-size effects. The competition between
surface tension and electron-shell effects leads to a complex landscape of
stable structures as a function of diameter, cross section, and temperature. By
considering arbitrary symmetry-breaking deformations, it is shown that the
cylinder is the only generically stable structure. Nevertheless, a plethora of
structures with broken axial symmetry is found at low conductance values,
including wires with quadrupolar, hexapolar and octupolar cross sections. These
non-integrable shapes are compared to previous results on elliptical cross
sections, and their material-dependent relative stability is discussed.Comment: 12 pages, 4 figure
Universality in metallic nanocohesion: a quantum chaos approach
Convergent semiclassical trace formulae for the density of states and
cohesive force of a narrow constriction in an electron gas, whose classical
motion is either chaotic or integrable, are derived. It is shown that mode
quantization in a metallic point contact or nanowire leads to universal
oscillations in its cohesive force: the amplitude of the oscillations depends
only on a dimensionless quantum parameter describing the crossover from chaotic
to integrable motion, and is of order 1 nano-Newton, in agreement with recent
experiments. Interestingly, quantum tunneling is shown to be described
quantitatively in terms of the instability of the classical periodic orbits.Comment: corrects spelling of one author name on abstract page (paper is
unchanged
The Escape Problem in a Classical Field Theory With Two Coupled Fields
We introduce and analyze a system of two coupled partial differential
equations with external noise. The equations are constructed to model
transitions of monovalent metallic nanowires with non-axisymmetric intermediate
or end states, but also have more general applicability. They provide a rare
example of a system for which an exact solution of nonuniform stationary states
can be found. We find a transition in activation behavior as the interval
length on which the fields are defined is varied. We discuss several
applications to physical problems.Comment: 24 page
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