LX11599
A New Look at Proton Conduction in Oxides
The conduction of hydrogen ions, or protons, is the underlying
mechanism behind the key technologies of hydrogen production, storage,
and energy conversion. In this study we have found that the proton-
tunneling rate - a key component of proton conduction - is closely
related to the vibrational dynamics of the hydrogen in the host
material. We find that when the proton's vibrational motion is
excited by infrared light of a specific, resonant frequency the
tunneling rate is increased dramatically. This colossal enhancement
could potentially improve proton conduction in important clean energy
devices such as fuel cells where a proton-conducting electrolyte
permits the migration of hydrogen ions and forces the electrons to
drive an electrical load such as a motor. Such an improvement in
conductivity would allow a lower operational temperature, a wider
choice of materials, longer cell life, and improved device
reliability. Our study presents a new method for observing proton
tunneling in solids and will be a starting point for future
investigations, both experimental and theoretical, relating proton
conduction mechanisms to hydrogen vibrational dynamics.
***
EU10299
New results for critical indices of fluids.
Fluids consist of a network of interacting particles on the microscopic level. In physics and chemistry it is a challenge of key interest to understand and determine the properties of such many-body systems as accurately as possible. Especially interesting are the properties close to the critical temperature and density, where determining these properties is a demanding task. The thermal properties in terms of temperature and density close to this point are expected to have so-called scaling behavior, which mathematically can be expressed through critical indices or exponents.
In this paper, a new method has been applied to obtain new values for the critical indices of fluids. Two accurate and related liquid state theories have been unified. Then, through the analyzes a new relation between the critical indices was found. Also, it was found that the critical index for the critical isotherm should be an integer odd number. Taken together, the critical indices became simple fractions and integer numbers. The novelty of this result is the simple numbers obtained for the indices. However, on one hand these numbers deviate somewhat from previous estimates, while on the other hand it is not ruled out that they are exact. Thus a central question is: Are these new numbers inaccurate, or is there need to modify previous estimates based on earlier analysis, simulations, and demanding experiments?
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LZ11710
*Lane formation in driven systems: From pedestrian zones to complex
plasmas*
The formation of “particle lanes” is a ubiquitous phenomenon occurring
in nature when two different species are driven against each other.
When the driving forces are strong enough, different particles exhibit
a remarkable self-organization – they start moving collectively,
forming interpenetrating “stream lanes”. The phenomenon – which is
commonly known from pedestrian dynamics in highly populated pedestrian
zones – occurs in very different systems of driven particles, ranging
from colloidal dispersions to molecular ions. In terms of the
individual particle dynamics, complex plasmas bridge the realms of
classic fluids and colloidal suspensions, and therefore can provide us
with invaluable insights into the new dynamical regimes of laning.
Recently, lane formation was studied in experiments performed on the
International Space Station using binary complex plasmas. By combining
the experiments and particle-resolved Langevin simulations, the
dynamical onset of laning was investigated. Furthermore, based on the
anisotropic scaling index analysis that is exceptionally sensitive to
symmetry changes occurring in particle ensembles, a universal order
parameter was proposed for the lane characterization. The use of such
an order parameter could be very useful for studying the onset of non-
equilibrium phase transitions occurring in various driven systems.
***
LV11730
Feeling photon forces with optical tweezers
Optical tweezers is a phenomenon where highly focused laser light
results in micron scale objects
(microbeads, biological cells, and even single proteins) being suspended
at the laser focus.
However, optical tweezers can also be used to feel the force that comes
from the momentum transfer
of photons. The photon as the quantum of the electromagnetic field also
acts as a particle that carries
momentum which it can impart on to any object. Such a feat is realized
in this work, where an
optically trapped bead covered with nano-sized silver islands is excited
by the laser in the presence
of probe molecules. The number of inelastically scattered photons from
the molecules is greatly
enhanced due to coupling to the metal. The result: the emitted photons
transfer momentum which
pushes the trapped bead off its equilibrium. The recoil forces are in
the range of 100 femtoNewtons
which is comparable to forces as tiny as the gravitational attraction
between two small glass spheres.
The technique demonstrates the use of optical tweezers as an alternative
measure for quantifying
light by relating it to mechanical force and can be applied to all forms
of spectroscopy.
***
LP11356B
Is disorder that messy?
Optical quasicrystals are structures with a modulation of the
dielectric function which
does not show any translational periodicity. These kinds of structures
are furthermore
typified by a high-order rotational and mirror symmetry. We
demonstrate that the optical
properties of quasicrystals find their origin in the optical behavior
of translationally
ordered crystals. In fact, it is possible to identify sub-structures
of the quasicrystal
which, arranged in a translational configuration, reproduce the same
transmission spectrum
of the quasicrystal itself. A number of questions arise then from this
finding: do quasi-
disordered structures differ that much from ordered ones? Can we still
assume that high-
order rotational symmetry of quasicrystals causes their typical wide
optical gaps? In order
to answer these questions we have analyzed the quasicrystals showing
the highest rotational
order known so far, namely 12-fold rotational symmetry. Our results
demonstrate that some
sub-parts of these quasicrystals, typically super-lattices with the
same local rotational
symmetry of the quasicrystals, show the same zero-transmission regions
of the quasicrystals
themselves. Hence, we can safely conclude that the typical wide optical gaps of
quasicrystals do not originate from their high rotational symmetry but
from the optical
properties of super-lattices. Moreover, in view of this finding, we
should also reconsider
the general misconception of quasicrystals as structures with exotic
optical properties."
***
LZ11271
Electrons with opposite spins move in opposite directions
In one dimension, there are only two ways to move: left or right. This
leads to some peculiar properties for one-dimensional systems on the
atomic scale. In our paper we present a one-dimensional conductor
forming on a bismuth surface, which effectively separates the
electrons going through it according to their spin, a kind of rotation
around the electron's axis. It turns out that electrons going to the
left have exactly the opposite spin as electrons going to the right.
Such a situation could have useful applications in the field of
spintronics, a novel type of electronics which is based on the
electron's spin rather than its charge and which could lead to more
effective computers or even quantum computing. The state reported here
is in several ways similar to so-called edge states appearing in the
recently discovered quantum spin Hall effect but instead of being
found for a sandwich structure of semiconductors at very low
temperatures, it is found on a simple, clean surface, is truly one-
dimensional and, most remarkably, even exists at room temperature.
