LR11774BR
Dissipationless flow of electrons---one by one
Electrons can flow without dissipation between two superconductors in
close proximity by transferring a pair of electrons---known as Cooper
pairs---at a time, a phenomena known as Josephson effect. We
theoretically discovered a dissipationless one-by-one electron
transfer from one superconductor to the other giving rise to
``fractional Josephson effect''. This occurs when the two neighboring
superconductors are connected by a new state of matter called a
topological insulator, which was theorized in 2005 and experimentally
discovered a year ago. The usual two-charge transfer occurs because
two electrons tend to bind together and form a Cooper pair inside a
superconductor. The new single-charge transfer that we predict is
possible because an individual electron finds an extra zero energy
"Majorana bound state" to stay at the interface between the
superconductor and the topological insulator. Our prediction can be
readily tested in future experiments
***
LX11765
Imaging Beyond the Diffraction Limit by Resistive means
Diffraction sets a fundamental limit to the resolution of an imaging system, restricting the ability to discriminate objects smaller than a wavelength. Here we present an approach for subwavelength imaging using a mundane conducting film as a natural optical superlens. It is theoretically predicted that near field sub–diffraction-limited imaging is possible as the film allows the recovery of critical evanescent waves that define a sharp image. This happens because space acts like a low pass filter for highly evanescent field components, and if a sheet or thin layer of imperfectly conducting material is placed adjacent to a source, such that the layer overcomes the larger impedance of the spatial low pass filter, no relative attenuation of evanescent components is experienced at the location of the sheet, resulting in a very sharp image (spot sizes of roughly 5% of the illumination wavelength are observed). The conducting layer enables us to trade definition for amplitude. Impedance sheets are commonplace in RF/microwaves, hence the phenomenon identified here is widespread, and can be easily extended into the Infrared and Terahertz regions, as well as to other areas of Physics where wave motion exists.
***
LW11257B
Spontaneous localization of dynamic energy in a simple ionic crystal
It has been shown over the last decade that driving a discrete
nonlinear lattice can cause dynamical energy to spontaneously
localize. A fundamental question in condensed-matter sciences and
nonlinear dynamics is whether or not such intrinsic localized modes
(ILMs) can appear in an atomic lattice in thermal equilibrium.
Neutron scattering measurements of He-4 and in alpha-U at high
temperatures have indicated new modes, possibly attributable to ILMs,
but these interpretations remain speculative since realistic models
of the nonlinear lattice dynamics are not available. These systems
are also exceptional in that both exhibit many exotic phenomena;
alpha-U is the only element to exhibit a charge density wave and
solid bcc He-4 is a quantum solid. The occurrence of new modes in
either of these systems, while interesting, does not have broad
implications since the underlying cause is related to rather unique
properties. By contrast, here we report the experimental observation
of ILMs in a remarkably simple ionic crystal, NaI, at high
temperatures and further show that these results are consistent with
realistic molecular dynamic simulations. Our work presents the first
observation of intrinsic 3-D localization requiring only discreteness
and nonlinearity in an atomic solid.
***
LZ11265AJ
Can relativity bother quantum cryptography?
Modern physics is dominated by quantum mechanics and relativity.
This is fair to say that Bell inequalities probe one of the deepest
aspects of quantum mechanics. The genesis of the Bell's discovery
can be traced back to the Einstein, Podolsky and Rosen seminal
paper about the completeness of quantum mechanics. They have
argued there that quantum mechanics would not provide a complete
description of nature if locality is assumed. Quantum mechanics
had to wait thirty years to be vindicated by John Bell who introduced
the inequalities which allow to test quantum mechanics against
competitive local hidden variable theories. If the spooky quantum
mechanical effect named entanglement [where non-causally related
particles can influence one another (see PHYSICAL REVIEW FOCUS,
27 December, "Spooky at any speed")] were correct, Bell inequalities
would be necessarily violated. Remarkably Bell inequalities have
been shown to be violated by 30 standard deviations, which strongly
supports quantum mechanics.
On the other hand, the fact that causally disconnected particles
can influence one another if they are quantum mechanically entangled
has raised an intense debate on the interplay between relativity and
quantum mechanics. In our work "Influence of detector motion in Bell
inequalities with entangled fermions", we investigate how relativity
influences the spin correlation of entangled fermions measured by
moving detectors. Suppose the physical situation where two entangled
spin-1/2 electrons described by wave packets fly in opposite directions.
At some point when they are far away one from the other (and thus
causally disconnected) each particle finds a spin detector. Although
actual experiments confirm that Bell inequalities are violated as
predicted by quantum mechanics when the detectors lie at rest,
we show that quantum mechanics will predict a quite different
output if the left and right spin detectors are set in fast enough
relativistic motion, namely, the CHSH Bell inequality will be
*satisfied* rather than violated.
Entanglement of quantum systems is currently used in many applications
including quantum cryptography protocols which is beginning to be
commercially traded. As technology develops, we expect that
quantum cryptography will be used to exchange messages around
the globe with the help of satellites. Because they move fast with
respect to the Earth surface, our work anticipates that relativity
should play some role here. This is difficult to anticipate at this
point whether or not this is going to be a protagonist one as in the
GPS case.
***
BZ10846
Listening to Underground Phonons
Ultrathin metal films on stiffer substrates can guide various kinds of
sound waves, some travelling at the surface, some underneath, and some at
the interface with the substrate. Not just the surface waves, largely
exploited in surface acoustic wave (SAW) devices, but especially their
sub-surface companions promise a future in novel electro- and
opto-acoustic devices, thus widely extending their application spectrum.
However, the rich family of sub-surface phonons remained so far elusive to
current surface probes such as electron energy loss spectroscopy. It comes
now as a surprise that the gentlest of all surface probes, helium atom
beams, can actually measure the dispersion of most sub-surface phonons.
Although He atoms merely tickle the surface a few Ångstroms above the
topmost atoms, they perceive the motion of the underground atoms via the
electron density oscillations at the surface. This mechanism, first
pinpointed in a previous study on the surface of copper, is now found
to work best with ultrathin lead metal films. Its electrons are highly
responsive to atomic motion making lead the element with the second
highest superconducting transition temperature (7.23K). Since this
responsiveness, shared by most metals, governs many thin-film transport
phenomena, measuring underground phonons is not only a significant step in
surface spectroscopy, but also points the way towards new nanometric
devices.
Friday, April 3, 2009
Wednesday, April 1, 2009
April 1, 2009
LX11061
New insight into how atoms move in highly-ordered binary compounds
Atom movement in solid compounds has many applications in technology. Most
often, atom movement takes place through the presence of a very small number
of lattice vacancies into which neighboring atoms can jump, like a slide
puzzle. In a highly ordered compound of two elements, A and B (think of
sodium chloride), different sequences of jumps are possible depending on
whether the vacancies are on A-sites or B-sites. In this paper, we show a
way to determine whether A-site or B-site vacancies are primarily
responsible for long range atom movement. Furthermore, we carried out
measurements on a series of compounds of rare-earth elements with indium and
found that A-vacancies are responsible for long range movement at one end of
the series while B-vacancies are responsible at the other end. This
remarkable finding is unexpected in light of the great chemical similarity
of rare-earth elements.
***
LU11918
A Zoo of Carbon and Oxygen
As the use of carbon-based nanotechnology is becoming ever more
prevalent, insights into how graphene, carbon nanotubes, and other
carbon-based materials behave in an oxygen atmosphere is ever more
important. This work investigates the oxidation mechanism of graphene,
specifically how oxygen interacts with its basal plane. The results
indicate that the perfect regions on the basal plane are inactive, but
that oxygen is able to attack vacancies. The reaction path proceeds in
two stages: all dangling bonds and those under stress are firstly
saturated with oxygen, and large oxygen functional groups subsequently
evolve. This work also shows that these groups also follow a strict
energetic hierarchy, which is split between the two stages. The dominant
reaction mechanism is suggested by the nature of the hierarchy, and is
expected to be generally valid for a number of sp2-bonded nanomaterials.
This detailed knowledge about possible oxidation sites on graphene and
the resulting functional groups is a critical piece of information for
nanoscience - just about every device comes into contact with the
atmosphere.
***
LR11546E
Is Jarzynski's Equality Practical For Free Energy Reconstruction?
The atomic force microscope (AFM) is a tool that uses a tiny,
needle-like tip to catch and manipulate single proteins. When a
protein is caught and stretched like a rubber band we can measure the
amount of force needed to stretch the protein. Jarzynski's equality is
a formula used to analyze this data to determine the amount of energy
needed to stretch and unfold a protein. This is important because this
information can help us understand the way proteins fold and unfold,
as well as tell us how certain proteins may function and behave in the
human body.
***
LW11013B
Optics Clues to Pairing Glues
One of the hottest questions in condensed matter physics is: What
causes superconductivity in cuprate superconductors with an
exceptionally high Tc (the temperature above which the material
becomes a normal conductor)? We obtained a precise answer to this
question by measuring and analyzing optical spectra of a large number
of high Tc superconducting materials.
Supercurrents are carried by bound pairs of electrons. Binding of two
electrons can occur if an electron polarizes its surrounding medium,
and a second electron is trapped inside this polarization cloud. This
induced polarization depends in general on the motional energy of an
electron. We deduced from our optical spectra the amplitude of the
induced polarization as a function of electron energy.
The main novelty is that we prove that aforementioned formalism
enables us to make detailed predictions: Firstly, if for a given
sample this relation was determined from the optical data taken at,
say room temperature, we can tell exactly what the optical spectra
will look like at all other temperatures. Secondly, knowing these
polarization amplitudes we were able to predict Tc and compare it to
the actual value. These predictions are ‘only’ two times higher than
the actual Tc’s, which is very good considering that, among other
things, we have not taken into account the effect of impurities which
are know to strongly reduce Tc.
A related hotly debated issue is, whether aforementioned polarization
is an elastic deformation of the crystal structure, or a so-called
spin-polarization (a magnetic effect). While we obtain indications in
our data for both types, we also observe in the so-called overdoped
samples that the elastic deformation effect is much too weak to
explain Tc, while Tc is still very high. We therefore can eliminate
elastic deformation as “the mechanism of high Tc” in favour of the
other possibility: High Tc superconducting pairing is mediated by
spin-fluctuations.
***
AA10400
Orienting molecules with a one-two laser punch
Spatial orientation of molecules is a pervasive issue in chemical physics
and, by breaking inversion symmetry, has major consequences in nonlinear
optics, allowing sum frequency generation for example. In this paper, we
propose and analyze a new approach to create an oriented sample of
molecules. Present laser techniques are good at aligning molecules, i. e.
making each molecule stand parallel to the rest. Still, out of a large
ensemble, half the molecules will stand on their feet, and others will
stand on their heads. In this work, we show how a combination of tailored
and timed laser pulses hitting the molecules in a one-two punch manner can
be used to selectively remove molecules with an unwanted orientation.
Specifically, subjecting an aligned molecule to a tailored infrared laser
pulse creates a pair of coherent wavepackets that correlate vibrational
phase with the head-up or head-down orientation. Subsequent, suitably
phased ultraviolet pulses dissociate molecules that have their bonds
stretched, thereby "weeding out" one but leaving intact the other
orientation.
New insight into how atoms move in highly-ordered binary compounds
Atom movement in solid compounds has many applications in technology. Most
often, atom movement takes place through the presence of a very small number
of lattice vacancies into which neighboring atoms can jump, like a slide
puzzle. In a highly ordered compound of two elements, A and B (think of
sodium chloride), different sequences of jumps are possible depending on
whether the vacancies are on A-sites or B-sites. In this paper, we show a
way to determine whether A-site or B-site vacancies are primarily
responsible for long range atom movement. Furthermore, we carried out
measurements on a series of compounds of rare-earth elements with indium and
found that A-vacancies are responsible for long range movement at one end of
the series while B-vacancies are responsible at the other end. This
remarkable finding is unexpected in light of the great chemical similarity
of rare-earth elements.
***
LU11918
A Zoo of Carbon and Oxygen
As the use of carbon-based nanotechnology is becoming ever more
prevalent, insights into how graphene, carbon nanotubes, and other
carbon-based materials behave in an oxygen atmosphere is ever more
important. This work investigates the oxidation mechanism of graphene,
specifically how oxygen interacts with its basal plane. The results
indicate that the perfect regions on the basal plane are inactive, but
that oxygen is able to attack vacancies. The reaction path proceeds in
two stages: all dangling bonds and those under stress are firstly
saturated with oxygen, and large oxygen functional groups subsequently
evolve. This work also shows that these groups also follow a strict
energetic hierarchy, which is split between the two stages. The dominant
reaction mechanism is suggested by the nature of the hierarchy, and is
expected to be generally valid for a number of sp2-bonded nanomaterials.
This detailed knowledge about possible oxidation sites on graphene and
the resulting functional groups is a critical piece of information for
nanoscience - just about every device comes into contact with the
atmosphere.
***
LR11546E
Is Jarzynski's Equality Practical For Free Energy Reconstruction?
The atomic force microscope (AFM) is a tool that uses a tiny,
needle-like tip to catch and manipulate single proteins. When a
protein is caught and stretched like a rubber band we can measure the
amount of force needed to stretch the protein. Jarzynski's equality is
a formula used to analyze this data to determine the amount of energy
needed to stretch and unfold a protein. This is important because this
information can help us understand the way proteins fold and unfold,
as well as tell us how certain proteins may function and behave in the
human body.
***
LW11013B
Optics Clues to Pairing Glues
One of the hottest questions in condensed matter physics is: What
causes superconductivity in cuprate superconductors with an
exceptionally high Tc (the temperature above which the material
becomes a normal conductor)? We obtained a precise answer to this
question by measuring and analyzing optical spectra of a large number
of high Tc superconducting materials.
Supercurrents are carried by bound pairs of electrons. Binding of two
electrons can occur if an electron polarizes its surrounding medium,
and a second electron is trapped inside this polarization cloud. This
induced polarization depends in general on the motional energy of an
electron. We deduced from our optical spectra the amplitude of the
induced polarization as a function of electron energy.
The main novelty is that we prove that aforementioned formalism
enables us to make detailed predictions: Firstly, if for a given
sample this relation was determined from the optical data taken at,
say room temperature, we can tell exactly what the optical spectra
will look like at all other temperatures. Secondly, knowing these
polarization amplitudes we were able to predict Tc and compare it to
the actual value. These predictions are ‘only’ two times higher than
the actual Tc’s, which is very good considering that, among other
things, we have not taken into account the effect of impurities which
are know to strongly reduce Tc.
A related hotly debated issue is, whether aforementioned polarization
is an elastic deformation of the crystal structure, or a so-called
spin-polarization (a magnetic effect). While we obtain indications in
our data for both types, we also observe in the so-called overdoped
samples that the elastic deformation effect is much too weak to
explain Tc, while Tc is still very high. We therefore can eliminate
elastic deformation as “the mechanism of high Tc” in favour of the
other possibility: High Tc superconducting pairing is mediated by
spin-fluctuations.
***
AA10400
Orienting molecules with a one-two laser punch
Spatial orientation of molecules is a pervasive issue in chemical physics
and, by breaking inversion symmetry, has major consequences in nonlinear
optics, allowing sum frequency generation for example. In this paper, we
propose and analyze a new approach to create an oriented sample of
molecules. Present laser techniques are good at aligning molecules, i. e.
making each molecule stand parallel to the rest. Still, out of a large
ensemble, half the molecules will stand on their feet, and others will
stand on their heads. In this work, we show how a combination of tailored
and timed laser pulses hitting the molecules in a one-two punch manner can
be used to selectively remove molecules with an unwanted orientation.
Specifically, subjecting an aligned molecule to a tailored infrared laser
pulse creates a pair of coherent wavepackets that correlate vibrational
phase with the head-up or head-down orientation. Subsequent, suitably
phased ultraviolet pulses dissociate molecules that have their bonds
stretched, thereby "weeding out" one but leaving intact the other
orientation.
Monday, March 30, 2009
March 30, 2009
LX11472
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.
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.
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