Strained layers curl up into hyperlenses
Rolled-up three-dimensional metamaterials with tunable plasma frequency
might pave the way to the realisation of hyperlenses working in the visible
regime.
We propose and demonstrate that three-dimensional radial metamaterials can
be created in a strain relaxation process by rolling-up planar
metal-semiconductor double layers with multiple rotations. The walls of the
resulting rolled-up-carpet like structures represent high quality
three-dimensional radial superlattices with accurately tunable unit cells
and lattice constants. Transmission experiments through these superlattices
reveal that they can be described as radial metamaterials with an effective
plasma frequency which is, in contrast to natural metals, not restricted to
the ultra violet but tunable over a broad range in the visible regime by
adjusting the ratio between metal and semiconductor layer thickness.
Effective-medium-picture-based considerations to use these radial
metamaterials as easy to process freestanding hollow hyperlenses for the
visible are confirmed by finite difference time domain simulations.
***
LW10937
Studying Spectacular Exploding Stars
Using the Daresbury Recoil Separator and Holifield Radioactive Ion Beam Facility at Oak Ridge National Lab, we have directly measured a nuclear reaction with radioactive nuclei crucial to our understanding of exploding stars. In stars that are denser, hotter and smaller than the sun, like the "Pup Star" Sirius B, thermonuclear runaways can occur once the temperature and pressure on the surface are high enough. These nuclear explosions, known as novae, release huge amounts of energy, and create lots of radioactive isotopes which are expelled into space. In order to understand just how powerful these explosions are and how much of any given isotope they produce, we have to know the rates of the nuclear reactions taking place. Usually, we have to measure these rates indirectly because of the almost insurmountable difficulties involved; but for the first time we have measured directly the rate of proton capture on radioactive fluorine-17, an important step in the chain of nuclear reactions during these explosions.
***
LW11137
Quantum Ghosts Are Useful
The idea that far distant particles can somehow 'talk' to each other so
perturbed Einstein that he called such weirdness 'spooky action'.
Scientists today are learning how to use the quantum entanglement that
gives rise to spooky correlations as a resource and now a team of
physicists at the University of Bristol have harnessed this phenomenon to
shed light on another unusual and previously intractable aspect of quantum
physics - that of distinguishing between two similar quantum operations.
In the everyday world any process can be visualised as some black box with
an input and an output; if you would like to identify a box you simply
apply some input, measure the output and deduce what happened in between.
But quantum black boxes are different. Distinguishing between two quantum
black boxes that are similar can be impossible with only single particle
inputs since it is not generally possible to then distinguish the different
outputs. The Bristol team demonstrate how distinguishing between two
similar quantum boxes becomes possible when quantum entanglement is used.
Apart from providing insight into the fundamentals of quantum physics, this
work is also crucial for future quantum technologies - how else could a
future quantum engineer build a quantum computer if she can't tell which
circuits she has!
***
LB11950
A new quasiparticle state found in oxide nanostructures
Oxide heterointerfaces frequently produce unexpected and unusual
electronic and magnetic states: magnetic, orbitally ordered, charge
ordered, and conducting behavior that is borderline between insulating
and magnetic, with the metal-insulator transition be triggered by
subtle effects. Nanolayers of VO2 provide a distinctly different class
of novel phenomenon in oxide nanostructures: (1) the ions are not
pushed away from their formal valence state, so there is no impending
"polar catastrophe," (2) a topologically distinct electronic structure
results for a specific thickness of VO2 slab encased in insulating
TiO2: a single point in (momentum) k space separates filled and
unfilled states. This point Fermi surface is analogous to the Dirac
point in graphene, but is even more unusual. First, the VO2 slab is
half metallic -- only majority spin states appear near or at the Fermi
level. Second, the (two dimensional) dispersion of the two bands away
from the point is Dirac-like (linear) along one principal axis, while
it is effective-mass-like (quadratic) along the other. This
"semi-Dirac point" carries with it different transport properties than
a Dirac
point, different behavior with doping, different behavior in a
magnetic field. This unique new state displaying a novel type of
quasiparticle behavior is a theoretical discovery, but there is strong
reason to expect it to be realizable with current technology.
Especially because it is a magnetic, conducting, nanoscale system, it
could well have applications in the spintronics arena.
***
LZ11496
Bouncing atoms off of light
In this paper, we demonstrate the ability to “bounce” atoms off of
light. Whenever atoms scatter light, they get a momentum kick that
can be used to manipulate their motion. With careful control, the
kicks can be made very precise and repeatable. We applied this
technique to atoms that were falling in gravity. We dropped the atoms
and, when they were moving at the correct speed, applied a laser pulse
that reversed their motion just as if they had bounced off a surface.
Eventually gravity pulled the atoms back down, and the pulse was
applied again. This could be repeated up to a hundred times before
the atoms were lost due to imperfections in the laser... many more
bounces than you can get with a rubber ball. The bouncing technique
has a number of potential uses. We explored the measurement of
gravity, which has applications in geophysics, energy exploration, and
inertial navigation. We could obtain the strength of gravity simply
by measuring the time interval between the bounces. Other possible
applications include simulating zero-gravity (without the expense of
spaceflight), cooling the atoms to the lowest possible temperatures,
and improving the accuracy of atomic clocks.
***
LV11622B
Information content in x-ray emission spectra of liquid water.
Ab initio molecular dynamics simulations are used to evaluate the claims
from x-ray spectroscopy of liquid water.
Recent high-resolution oxygen x-ray emission spectra show two distinct
lone-pair peaks for liquid water.
Does the fine-structure in oxygen K-edge x-ray emission imply that
liquid water is a two-component mixture
or is it the signature of a transient OH species arising in the
core-excitation process?
Just as the interpretation of x-ray absorption of liquid water, this
question is intensely discussed in the x-ray
spectroscopy community, because x-ray emission is an independent probe
of the electronic structure containing
complementary information. In this paper, ab initio molecular dynamics
simulations are used to show that the water
lone-pair features are of fundamentally different origin. One is
primarily due to the lone-pair of the intact water
molecules, the other is assigned to a transient OH species formed by
ultra-fast photo-dissociation.
Hence, x-ray emission cannot be taken as evidence of a two-component
mixture model of liquid water with classes
of molecules in distinctly different H-bond environment. Instead x-ray
emission is a unique technique to study
the ultra-fast response to high-energy radiation.
***
EX10270
But, just where is the interface?
For several years now, molecular computer simulations have been providing a
wealth of information about phase coexistence: the conditions at which two
phases are simultaneously stable, and the details concerning the molecular
region that separates them: the interface. For instance, "explicit
simulations of interfaces" are able to directly model interfaces, such as the
liquid-vapor interface. However, it turns out that the exact location of the
interface is delicate to define, at least in mathematical terms. In this
paper, a new proposal employs concepts taken from the field of
computational geometry, where the definition of the "shape" of a set of
points is a well-known problem. In particular, the alpha-shape construction,
which was originally introduced in order to identify the boundary of a set of
points, is used in order to define our interfacial molecules.
Image Caption: A snapshot from a simulation of liquid-vapor coexistence of a model
for noble gases. Solid spheres are the atoms that are identified to be "at"
the surface by our method. Also shown, the interface is modeled by the
triangulated surface (red triangles and blue ridges).
***
LY11398B
Photoionization can be a useful tool for studying single-electron
transistors and other nanodevices
In this paper, we demonstrate for the first time, based on theoretical
results, that photoionization can be a useful tool to investigate
single-electron transistors, and encourage experimentalists to use it for
these and other devices of interest for nanoelectronics. The reason is
that photoionization permits to obtain information on how many electrons
occupy a quantum dot and the charging energy in a direct manner. This is
very important, because experiments carried out up to now, which measure
the electric conductance, only allow to determine these quantities
indirectly. It is worth emphasizing that in the photoionization processes
considered by us, an electron absorbs a photon with energy of the order of
the work functions (typically, 1 eV) and is ejected into the vacuum. This
phenomenon is completely different from the widely studied photo-assisted
tunneling considered by previous investigators, involving much lower
photon energies (typically, a few meV). We give concrete suggestions on
how to conduct experiments using photoionization alone or in combination
with transport measurements. Monitoring zero kinetic energy (ZEKE)
photoelectrons is especially recommended, because ZEKE--spectroscopy
offers a better resolution than standard photoemission.
***
BZ10479
Graphene Stays Cool No Matter What
It was recently discovered experimentally that graphene, which is just a
single layer of carbon atoms arranged in a honeycomb pattern, exhibits far
better thermal conductivity than any known material including diamond and
carbon nanotubes. This discovery opened a new window to graphene
applications in electronics and thermal management. At the same time, the
physical mechanisms behind this superior thermal property of graphene
remained a mystery. In this paper, we have shown theoretically that the
dynamic properties of graphene crystal lattice and its strictly
two-dimensional nature are responsible for extremely high thermal
conductivity of graphene. Phonons, quanta of crystal lattice vibrations,
which carry heat in graphene, propagate with high velocities and do not
scatter as strongly as they do in conventional three-dimensional bulk
crystals. We also explain why the thermal conductivity of graphene depends
on the width of graphene flakes. The results of the paper help to pave the
way for graphene applications in heat removal from electronic chips. The
chip overheating is now one of the most serious problems faced by the
electronic industry.
***
LT11155BR
The parent compounds of high-Tc cuprates become superconducting!
The parent compounds of high-Tc cuprates have long been
considered to be antiferromagnetic Mott insulators. For example,
La2CuO4 with the K2NiF4 structure is an insulator with no doubt.
R2CuO4 (R: rare-earth element) with the Nd2CuO4 (abbreviated usually
as T’) structure has also been believed as a Mott insulator since
the discovery of “electron-doped” superconductors, T’-(R,Ce)2CuO4
in 1989. Our recent work, however, has demonstrated T’-R2CuO4 to be
superconducting. The origin of the sharp contradiction between the
past and our results can be traced to impurity oxygen at the apical
site. Impurity oxygen atoms in T’ cuprates play the role of a very
strong scatterer as well as a Cooper-pair breaker. Therefore the
generic behavior of T’-cuprates can be reached only after complete
removal of impurity oxygen atoms. We employed a new thin-film
process, low-PO2 firing followed by low-temperature reduction, to
clean up impurity oxygen atoms, then achieved superconductivity in
the parent compounds, T’-R2CuO4. Our results, although further
works are required, throw strong skepticism on the currently accepted
“doped Mott-insulator” scenario for high-Tc superconductivity:
high-Tc superconductivity develops upon doping of either holes or
electrons in Mott-Hubbard insulators
***
LA11699
The Knizhnik-Polyakov-Zamolodchikov Formula Finally Proven
The famous KPZ formula appeared in 1988 as a striking application of
string theory to two-dimensional statistical mechanics: it predicted the
existence of a precise relation between the fractal dimension of a
random subset of the plane and its dimension in the presence of
two-dimensional quantum gravity. More than twenty years after its
discovery, this formula is finally rigorously proven in this paper,
within the realm of probability theory and Liouville quantum gravity.
In Liouville quantum gravity, the usual Euclidean area element dxdy of
the standard xy plane is replaced by a quantum area element,
dA=exp[h(x,y)] dxdy, where h(x,y) is the so-called Gaussian free field,
a stochastic two-dimensional generalization of Brownian motion.
Measuring geometrical sets with this quantum metric is tantamount to
randomly exploring very high mountains and very deep valleys at all
(infinitesimal) scales. In this paper, the proof rests on a fine
mathematical analysis of the local averages of the 2D Gaussian free
field. By focusing on the average values of the field restricted to
concentric circles, we reduce the problem to a calculation involving a
standard one-dimensional Brownian motion.
Perhaps most surprisingly, our method shows that the KPZ formula holds
for all planar fractals, and not only for restricted classes of
conformally invariant sets, as originally assumed. Several of the most
fundamental open problems in 2D quantum gravity (such as proving that
"discrete quantum gravity" based on random triangulations has Liouville
quantum gravity as a continuum limit, and identifying the geometrical
nature of quantum geodesic paths) can now be precisely formulated and,
we hope, settled using the framework we introduce here.
***
LC12080
From three to four: a quantum leap in few-body physics
Already in the 1970's, the Russian theorist Vitaly Efimov found a
stunning solution to the quantum three-body problem, predicting a series
of ultra-weakly bound trimer states. It took more than 35 years until
first evidence of the mysterious "Efimov" three-body states was found in
ultracold samples of optically trapped Cs atoms (Kraemer et al.,
Innsbruck, 2006). After this long time the field is now taking off at an
amazing speed, and an increasing number of ultracold atomic and
molecular systems reveal traces of Efimov states.
The addition of a further particle, the step from three to four bodies,
leads to an enormous increase in complexity with great challenges for
its theoretical description. Recently, two theory groups (Hammer and
Platter, Bonn & Ohio, 2007; von Stecher, D'Incao, and Greene, Boulder,
2008) predicted the existence of pairs of four-body states being closely
tied to Efimov trimers. The experiment of the Innsbruck group now
confirms the central theoretical predictions. The results on
recombination in an ultracold gas of cesium atoms show a pair of
resonances caused by four-body processes as fingerprints of the
predicted pair of four-body states.
***
LV11317A
Linking algebra of qubit pairs to projective geometry
A coupled pair of quantum spins ("qubits") describes many
interesting phenomena in quantum cryptography, quantum teleportation,
and quantum computing. These topics are also increasingly of applied
interest. The mathematics that physicists use in these descriptions
is called Lie and Clifford algebras. However, other branches of
mathematics such as projective geometry and design theory have not
been associated with qubits. But this paper points out such links,
and also to a set of "hypercomplex" numbers called octonions (which
are generalizations beyond reals, complex numbers and quaternions,
all of which have applications throughout physics). A striking
feature of projective geometry is a duality between points and lines
so that any valid theorem remains so upon interchanging points and
lines (not true of ordinary geometry). Thus, a diagram of seven
points and seven lines, with each point lying on three lines and each
line containing three points, occurs both as the smallest projective
plane and for describing the multiplication table of the seven
octonions. This diagram is now linked in this paper to one of the
algebras involved in quantum logic gates built out of two qubits.
These connections may be mutually exploited in both Lie algebras and
projective geometry.
***
LZ11585A
SUDDEN DEATH AND SUDDEN BIRTH OF ENTANGLEMENT WITH MEMORY
Entanglement is "the characteristic trait of quantum mechanics", as
Schrödinger stated almost a century ago. It constitutes a key resource
for a number of applications of modern physics, offering a new way of
transmitting information and performing controlled interactions on
quantum bits. Entanglement will certainly be an essential ingredient in
the realization of quantum computers.
However, quantum properties are very fragile, decoherence is
omnipresent, and sometimes entanglement can be completely destroyed in a
finite time. So in order to control decoherence and preserve
entanglement, a deep understanding of the disentanglement process in
realistic situations must be achieved.
In our paper we study the exact entanglement dynamics of two quantum
bits (qubits) in a common environment characterized by memory, for
example two atoms in a leaky cavity. Such a system exhibits interesting
features as the resurrection of the qubit-entanglement after a period of
death, or the revivals of disentanglement after the sudden birth of
entanglement. Our results shed new light on the role that the
environmental memory plays in the entanglement dynamics, and might help
to understand how to exploit such a crucial resource in the future.
***
EX10283
Capsule in micro channel flow
In this paper, we investigated the initial motion of capsule in micro channel flow just after release by a novel numerical simulation method, which combines two methods, one for solving the mechanical problem of fluids inside and outside the capsule membrane, and the other for tracking the capsule membrane. Studying the motion of capsule in micro channel flow is quite important in physics, physiology, and pharmaceutics. For example, it may deepen our understanding of red blood cell behavior in blood vessels. Our results show that the capsule behavior depends on initial capsule shape, initial capsule position, and membrane mechanical properties. Off-center capsules, whose initial center positions are not on the center-line of tube, tend to migrate towards the tube center-line because of the influence of fluid flow. This leads to the development of a cell-free layer around the tube wall. At the same time, off-center capsules experience tank-treading motion, i.e. the membrane rotates around the interior fluid.
***
BZ10683
Magnetism at the interface between non-magnetic oxides.
In this paper we report the appearance of magnetism at the interface between two non-magnetic oxides due to a surface reaction. Mixing Co3O4 with TiO2 we found room temperature ferromagnetism despite the antiferromagnetic and diamagnetic character of both oxides respectively. The nice point of our work is that we do not need to claim a new kind of magnetic interactions to account for it but we can explain it with the well known theories of magnetism in oxides developed in the 60’s but applied to surfaces and interfaces instead of bulk materials. The key idea is that Co3O4 is very similar to Fe3O4 (which is magnetic at room temperature). The slight differences among them that make Co3O4 non-magnetic disappear when the Co3O4 is mixed with TiO2 due to a surface reaction with transfer of some electrons from one oxide to the other. Thus, a thin layer at the surface of Co3O4 grain becomes ferromagnetic. This surface magnetism “was always there” but now we are able create materials with a large fraction of surface atoms (for which the effect is significant) and we are now able to measure with a extreme precision that was not possible 40 years ago. Similar effects have been recently reported in epitaxial films (explained in terms of new magnetic ordering mechanisms) with a deep control of growing conditions but the possibility to arise them by simple mechanical milling we show here, will increase the possibilities to use and explode it for applications.
***
CB10204
The “middle-of-the-road” nucleus 106Zr
The article predicts the spectroscopic properties of 106Zr, an atomic
nucleus with 106 nucleons of which 40 are protons. As such, it is rich in
neutrons and short lived, and lying just at the limit of current detection
capabilities. Its interest resides in the fact that it sits right in the
middle between the ‘magic’ neutron numbers 50 and 82—numbers that define
the usual shells of a nucleus. According to novel theories, this
traditional shell structure may well be modified in very neutron-rich
nuclei that are increasingly being probed with radioactive-ion beams. So,
whether 106Zr behaves as a nucleus at mid-shell will ultimately depend on
the character—magic or not—of its far-away sibling 122Zr with 82 neutrons.
The comparison of our prediction with future experimental studies of 106Zr
might help to indicate whether the magic number 82 persists in the heavy
zirconium isotopes, long before the nucleus 122Zr itself will become
experimentally accessible.
***
LL11329
Does the zero-bias anomaly always signify Kondo physics?
Summary: Once a conductance peak at zero bias, the so-called zero-bias
anomaly (ZBA), is observed in various mesoscopic systems, it is immediately
associated with the intriguing Kondo effect. Here, in contrast, we show
this is not always correct and the ZBA observed in quantum wires is in fact
very different. This paper presents experimental evidence showing that the
temperature and magnetic field characteristics of the ZBA peaks in quantum
wires are inconsistent with Kondo physics. In addition, it is found that
the single ZBA peak still occurs in a fully spin-polarised regime in which
the Kondo spin-flip is prohibited. We demonstrate that a shift in
one-dimensional (1D) energy levels with source-drain bias can reproduce the
ZBA and, unlike the other systems, the 1D system does not need to have the
Kondo mechanism to give rise to a zero-bias conductance peak. This
manuscript is thus expected to have a significant impact on the general
understanding in this active field and to generate substantial interest in
the community.
***
BAR1150
Electrostatic Noise on the Nanoscale
As it becomes more common to fabricate and study electronic devices
on the nanoscale, techniques that can characterize and predict performance
become essential in understanding new phenomena and can lead to improvements
in fabrication and design. We show
that by using electrostatic force detection techniques one can pinpoint
areas over semiconducting surfaces where certain types of electric
charge noise are prominent.
Fluctuating charge is detected via the resulting electrostatic force by
measuring the resonance frequency of a small conducting cantilever placed
only a few nanometers away from the surface. This method of detection has
been shown capable of detecting the electrostatic force from single
electrons, and in this study has shown lateral resolution of at least 20 nm.
Cockins et al. also show that the noise characteristics can be influenced
by light. As charge noise is almost always detrimental to device operation,
and as the mechanism responsible for this particular type of charge noise is
instrumental in photovoltaic operation, the combination of electrostatic
force detection with surface mapping and optical excitation provides a means
to link nanostructure to device performance.
