6-4-08

BR10859
No escape for " relativistic" electron in graphene quantum dots!

The recent discovery of elusive two-dimensional form of carbon
called graphene has unusual electronic
properties that may be useful in the design of new electronic
devices. Electrons in graphene behave
as massless chiral fermions , i.e., ``relativistic'' electrons.
Due to this unique property, the electrons in graphene cannot
be localized by any confinement potential (Klein's paradox).
In this case we need to discuss not the localization but the
trapping of the electrons by confinement potential. The electron
trapping is strongly affected by the sharpness of the confinement
potential, the most efficient trapping is
realized in a smooth confinement potential and
for electronic states with large angular momentum.
Although it is easier to create a confinement potential with
smooth boundary, the quantum dots
with sharp boundary are also important. We show that
for the quantum dots with sharp boundaries there
is a completely new mechanism of trapping. This trapping is
due to interference effect and as a result, it can be observed
for all values of angular momentum.
For smooth boundary the trapping is due to a tunneling and can
be achieved only for large values of angular momentum.
We show that even in the case of
confinement potential with sharp boundaries we can realize the
trapping of the ``relativistic'' electron for a very long time.
For special parameters of the confinement potential, which
can be achieved by an additional tuning of the potential,
the escape rate from some states of the quantum dot can be
exactly zero. Therefore, the ``relativistic'' electrons
in such states are em strongly localized with
infinite trapping time. This localization is achieved
not due to a large trapping potential barrier, but due to
interference effects within the quantum dot.
This opens another possibility for tuning of the trapping
properties of an electron in graphene quantum dots.



***

LL10963
Trapping a rainbow in a simple broadband plasmonic structure

Artists and poets have often dreamed of holding a rainbow in their hand. Meanwhile, more practical engineers and scientists have sought to control pulses of light in novel optical circuits with nanoscale dimensions. In this paper, the authors attempt to do both, and present a detailed discussion of a relatively simple graded metal grating structure to realize such a dream. This structure is capable of slowing down or even stopping light waves over a very wide spectral band at different locations along the surface of the structure. The separation between the adjacent localized frequencies can be tuned freely by changing the grade of the grating depths. The propagation characteristics of these trapped surface modes can be controlled by the surface geometry. Such a feature could open a door to the control of the light wave on-a-chip or even realize novel applications such as a spectrometer integrated on-a-chip for chemical diagnostics, spectroscopy and signal processing applications. Importantly, the current graded grating structures developed for “trapped rainbow” storage of light in the THz domain could be scaled to telecom frequencies for future possible applications of integrated optical and nano-photonic circuits.


***

LL11055
How to reach consensus faster? Slow down!

Imitation of neighboring states ('opinions') may eventually lead to an
ordered state in a spin system ('consensus') - but sometimes it may
take an enormous time to reach consensus, dependent on the system
size. We present an interaction mechanism which allows to drastically
shorten the consensus time - by adding inertia to the individual
transitions. This is counterintuitive as it decelerates the dynamics
on the microlevel, but accelerates the ordering dynamics on the
macrolevel. We find that there is an optimal value at which the
individual 'stubbornness' has to grow over time, to maximize this
effect.



***

LL11471B
Knocking nonlinear modes into existence in uranium

Dynamical modes, which become thermally activated in uranium at high
temperatures, were successfully generated out of equilibrium in cold
crystals using x-ray and neutron scattering. Results show that these
modes are created by amplitude fluctuations that mirror the modes
themselves, providing the first direct evidence of the intrinsic
nature of a localized nonlinear lattice mode in a three-dimensional
crystal. The problem of localized modes in nonlinear lattices has
been of great intellectual interest since the 1950's and has been
studied by the greatest minds, beginning with the pioneering
simulations of Fermi, Pasta and Ulam at Los Alamos. This early work
was motivated not only by the existence of these breather-like modes,
but also by the implications that they pose to the ergodic hypothesis
and the foundations of statistical mechanics. The discovery of these
modes in real materials, however, has more pragmatic ramifications
and applications. Supporting data on uranium shows that these
nonlinear modes influence almost every property, including heat
capacity, thermal transport, thermal expansion, and possibly
mechanical deformation. The influence on thermal transport is
particularly exciting as it opens up new possibilities for the
manipulation of heat in next-generation energy technology. The scale
of the modes also suggests that they could be interfaced with
nanotechnology. Furthermore, evidence suggests that ILMs in uranium
may also act as an incipient driver for a solid-state phase transition.


***

BRR1100
Necktie gaps in modulated two-dimensional electron gas


A periodic potential modulation of two-dimensional electron gas (2DEG)
can give rise to the esthetic "necktie" gaps within the intersubband
single-particle excitations (SPEs). The necktie gaps are found to
center at the zone boundaries in the spectrum showing the excitation
energy vs. the Bloch vector. This phenomenon is apart from the known
minigap plasmons existing inside the gap between the intrasubband and
intersubband SPEs. These are very interesting characteristics of such
an anisotropic system with spatially modulated charge density and with
a weak sinusoidal tunneling in the energy dispersion. Such minigap
engineering makes these nanostructures to nanoplasma physics as
photonic bandgap crystals are to optics and sonic bandgap crystals
are to acoustics. One can also envision a tandem structure made up of
many such modulated 2DEG systems. The samples of such smaller
periodicity (with a period d < 30 nm) with persisting necktie gaps
would be useful as nanofilters and will allow neither the collective
(plasmon) nor the single-particle excitations to propagate in the
given frequency range.

***

BP10589B
Landau theory of crystallization and
the capsid structures of small icosahedral viruses

Viruses enclose their genetic material in a protective
protein coat called a capsid. Inside the infected cell
coat proteins self-assemble into a rigid spherical
shell with the symmetry of a regular icosahedron.
Since nearly fifty years virologists analyze protein
positions in icosahedral capsid structures using a
simple geometrical model by Caspar and Klug, which
imposes drastic limitations on the number and types of
possible structures. Recent advances in
cryo-electronic microscopy have evidenced however a
whole series of examples violating these rules. In the
present work we developed a model which describes in a
uniform way both the structures satisfying Caspar-Klug
rules and those violating them. For that aim we
generalized Landau theory of phase transitions, a
powerful tool which has been used by the physicists to
understand many problems of condensed matter physics,
to explain the protein self-assembly in icosahedral
viral shells. We established the method which
calculates the distribution of proteins in capsids and
clarifies their arrangement in the structures
violating old rules. An important influence of the
protein distribution in a capsid on the virus capacity
to infect the cell is illustrated.


***

LH11704B
Random medium may help in secure transmission of signals without coding

It is commonly believed that scattering prevents log-distance propagation of waves or quantum particles through random media. In absence of dissipation the amplitude of the time-inverted wave increases towards the source. We propose to explore this famous symmetry in secure communications. In one-dimensional case a wave propagating in random medium with mirror symmetry strongly decays towards the center of symmetry. Having passed the center, the wave hits the same scatterers but in the inverse order, i.e. it propagates “against time.” The amplitude of this wave increases towards the mirror image of the source, independently how far away the source and the image are. In random medium the wave decays exponentially due to the effect of Anderson localization, thus leading to strong suppression of the signal in close vicinity of the source. In this paper we show that two identical sets of resonant contours with random frequencies, being connected to the emitting and receiving ends of a transmission line, may provide secure communication without coding. The signal entering the line is suppressed to the level of noise and cannot be detected. But it is restored once it has passed through the receiving set of the contours.



***

BR10869
A pure 2D nucleation in semimetallic homoepitaxy of Bismuth

Due its fascinating electronic properties, thin films of the semimetal bismuth have enormous potential for applications in spintronic devices. As a firsthand demand, understanding of the growth processes of high quality thin films is necessary. In our present work we explain the microscopic processes and the parameters controlling the growth mechanism. Unlike most metallic systems, we observe a pure 2-dimensional nucleation even at low temperature (T = 80 K), from which we estimate a low step edge barrier in bismuth homoepitaxial growth. A threefold dendritic shape of the islands indicates a kinetic limitation of edge diffusion at such a low temperature, which can be overcome at higher temperatures (T > 300 K) changing the growth mode towards step-flow. This first study of growth mechanism on bismuth surfaces provides an excellent opportunity to the researcher for further investigation.

***

CD10135
Enhanced nuclear fusion rates within metals

Deuterium fusion reaction rates can be grossly enhanced within
metals. We established the verification of this finding under the
controlled conditions in accelerator experiments. It can be explained
by the electron screening effect which is well known in nuclear
astrophysics. It means that the repulsive force between the positively
charged nuclei is extenuated by the negative electrons in the
surrounding of the colliding nuclei thus lowering the Coulomb barrier
for the fusion. The dense electron gas in a metal lattice is more
effective than the electrons in a hydrogen molecule or a hot
solar-like plasma. Subsequently, also other groups made similar
experiments giving reason for a theoretical description attempt by a
model for stellar plasmas known as the Debye-Hückel model. Despite its
improperness for the frozen Fermi electron gas in the metal this model
was used to predict a method to remove nuclear waste by implantation
into metals at cryogenic temperatures. The possibly very high
movability of hydrogen in metals and target contaminations make
screening experiments very difficult and error-prone. In the paper we
present new experimental results, point out experimental pitfalls,
summarize our previous results and theoretical approaches including
extensive citations. We clearly showed that the Debye-Hückel model is
not appropriate for the description of the electron screening in
metals both for experimental and theoretical reasons. The
exponential-like enhancement of nuclear reaction rates in metallic
environments can make it possible to observe nuclear reactions between
charged particles even at room temperature.


***

LP11611
Who knew it would take nearly a century to create the Bohr atom?

The first successful model of the hydrogen atom was proposed by Danish
physicist Niels Bohr almost a century ago and comprised an electron in
classical circular "planet-like" orbit about the nucleus. With the
advent of quantum mechanics it was realized that the position of an
electron could not be precisely specified but rather it must be viewed
as being distributed within the atom. However, for highly excited
systems this microscopic quantum world should undergo a transition into
the macroscopic classical world. We have taken advantage of this to
produce the closest analog yet achieved to the Bohr model of the atom.
We manipulate atoms in highly excited Rydberg states using a
carefully-tailored series of short electric field pulses. Such Rydberg
atoms are the true giants of the atomic world having diameters
approaching micrometers and, if opaque, would be visible to the naked
eye. Starting with laser-excited quasi-one-dimensional Rydberg atoms we
have been able using electric field pulses to transfer the electron from
its initial highly elliptical orbit into a near circular orbit while at
the same time localizing the electron within this orbit. Measurements
show that the electron remains localized for several orbits and behaves
much as a classical particle. This creation of the Bohr atom illustrates
the power of atomic engineering using pulsed electric fields and has
potential applications in studies of classical and quantum chaos, of
information storage and processing in atoms, and of ultrafast
laser-matter interactions.



***

BR10658
A CASE OF KINETIC ARREST OF THE STRUCTURAL TRANSITION IN SHAPE MEMORY ALLOY

Magnetic shape memory materials are some ferromagnetic alloys in which,
large shape deformation is possible by an external magnetic field. The key
to their functional behavior is a structural transition called martensitic
transformation. We have studied one such alloy made up of Nickel,
Manganese and Tin. An interesting observation from our electrical
resistance measurement is that, on cooling the sample through the
martensitic transformation temperature in presence of an external magnetic
field, a fraction of the high temperature phase continues to persist down
to the lowest temperature of measurement. This is an example of kinetic
arrest of the high temperature phase by a magnetic field across a first
order phase transition such as martensitic transformation. The arrested
state was found to show very unusual metastable behavior along with a
tendency to transform into the stable low temperature phase. Surprisingly,
a close resemblance of this phenomenon is observed with the behavior of
some very different magnetic materials known as manganites. This scenario
is expressed in terms of a coupling between the magnetization and the
elastic strain, which produces an under-cooled state in materials with
strong magneto-structural correlations, such as manganites or the present
shape memory alloy.



***


LE11243B
Quantum dots squeezed into resonance

We demonstrate that local stress is a promising tool to apply energy shifts
to individual close-by semiconductor quantum dots in a deterministic
fashion. Semiconductor quantum dots lie at the heart of many exciting
devices and physical concepts, e.g. single photon sources, qubits, entangled
photons. A key task for almost all applications envisioned is a
deterministic control over the emission energy of individual quantum dots.
In our work we consider two quantum dots which are embedded into the wall of
a flexible micro tube optical ring resonator. Our calculations predict that
upon local deformation of the ring resonator reversible spectral shifts into
the red and blue of several tens of meV can be achieved (see schematic
attached). Depending on the relative position and magnitude of the applied
force the two quantum dots can be tuned into mutual resonance and into
resonance with the optical mode. These findings are experimentally
substantiated for In(Ga)As quantum dots with low density embedded in the
wall of a rolled-up micro tube ring resonator.

6-2-08

EP10452
Magnetic Biotransport for Gene Therapy

Magnetic nanoparticles are finding increasing use in bioapplications, primarily as carrier particles for biomaterials such as cells, proteins and DNA. In this paper we present a model for predicting the transport and targeting of biofunctional magnetic nanoparticles for the magnetofection process. In magnetofection, magnetic carrier particles with surface-bound gene vectors are magnetically attracted towards host cells for transfection (delivery of the transported DNA into the host cell). In in vitro magnetofection, the carrier particles/DNA are introduced into a host cell culture, where they experience a magnetic transport force, which is produced by a rare-earth magnetic element positioned beneath the culture. Magnetofection has significant advantages over traditional transfection methods: the process time is dramatically reduced, e.g., peak transfection levels can be achieved with a particle/cell incubation time on the order of 10 minutes, as compared to 2-4 hours for standard methods, high transfection rates can be obtained with significantly lower vector doses; an increase in the gene transfer efficiency of up to 5 orders of magnitude can be realized, and gene delivery can be achieved with non-permissive cells. The model developed in this paper provides a fundamental understanding of nanoscale magnetic biotransport, and enables the development and optimization of novel magnetofection systems for in vitro applications.


***

LQ11849

See the kinetics of self-assembly of molecules on surfaces

It has been well-known that ammonia molecules on Si surfaces are
self-assembled. The self-assembly has been tentatively or rigorously from
the quantum mechanical calculations considered as a result of the H-bond
interaction between the molecules. However, the atomic structure of the
molecules self-assembled on the surface has been highly controversial to the
surface scientists; the H-bonded linear chain structure is the lowest in
energy, but the zigzag chain structure is more preferential in experiments,
which consists of surprisingly no H-bond. In this paper, we show explicitly
that not only the H-bond but the covalent coordinate bond between the
ammonia molecule and the surface Si atom plays an essential role in the
self-assembly of the molecules. Surface chemical reactions on reactive
surfaces are typically irreversible and thus easily form an in-equilibrium
state. Therefore, searching for the low energy configuration sometimes
conducts us to a wrong conclusion. In order to see the kinetics of the
self-assembly, we investigated the detailed potential energy surfaces from
first-principles, and the experimentally observed zigzag feature is found to
be well described by the kinetics consideration.


***


EF10322
Elimination of biosensor fouling using acoustically driven flow field

All transducers used in biological sensing suffer from fouling resulting from non-specific binding of protein molecules to the device surface. Our research group at the Sensors Research Laboratory at University of South Florida has successfully identified a phenomenon which can potentially eliminate biofouling and increase the sensitivity of biosensors. Biosensors typically operate in liquid media for detection of biomarkers. In the current work, using a novel numerical technique as well as experiments, we have identified that fluid motion induced by high intensity sound waves, such as those propagating in these sensors, can lead to the removal of the non-specifically bound proteins thereby eliminating sensor fouling (Figures attached). This phenomenon, known as acoustic streaming, allows sensor re-use while also increasing its sensitivity and reducing the signal-to-noise ratio. We present a computational and experimental study of the acoustic-streaming phenomenon induced biofouling elimination by surface-acoustic-waves (SAWs). The transient solutions generated from the developed coupled-field fluid solid interaction model were utilized to predict trends in acoustic-streaming velocity for varying design parameters such as voltage intensity, device frequency, fluid viscosity and density. The model predictions were utilized to compute the various interaction forces involved and thereby identify the possible mechanisms for removal of non-specifically-bound proteins. Our study indicates that the SAW body force overcomes the adhesive forces of the fouling proteins to the device surface and the fluid-induced drag and lift forces prevent its re-attachment. The streaming velocity fields computed using the finite-element models in conjunction with the proposed mechanism were used to identify the conditions leading to improved removal efficiency. Our research findings have significant implications in designing reusable and highly sensitive biosensors.

***

AR10309
A Step Forward

Entanglement is a subtle and eluding property of quantum systems
comprising many parts. Entanglement induces correlations between the
measurable properties of different parts of a quantum system which cannot
be reproduced by any procedure involving only the local operations (LO)
and classical communication (CC) between various parts of any system.
In consonance with this, entanglement in a quantum system cannot increase
(or be created) via LOCC. This principle is connected to another
intriguing property of entanglement: a multipartite quantum system can
get entangled in various inequivalent ways, which cannot be transformed
into each other via LOCC. However, the most intimidating aspect of
entanglement is that it cannot be `built in parts¡|, that is, the
entanglement of N parts is not a sum or a simple function of the
entanglement of M (< N) partite subsystems.

In order to understand and use entanglement and its role in various
quantum phenomena involving many particle systems (eg. quantum phase
transitions, BE condensates etc.) we must be able to say how much
entangled a given quantum system is. In other words, we need a measure for
entanglement in a given system. Such a measure must respect non-increase
of entanglement under LOCC, apart from many other properties. Further, the
computation of entanglement measure should not be formidable. Such a
`good¡| entanglement measure is known only for bipartite pure states and
thanks to Wooters, for all two qubit states. Finally, a good entanglement
measure is expected to be determined experimentally, without prior
knowledge of the system¡|s state. A detailed specification of the state of
a quantum system is a formidable task unless you already know the state.
It is very unlikely that in an actual application, eg. quantum
communication, the intermediate states of the quantum system could be
specified in detail.
In this paper we have proposed a measure of entanglement for N-qubit pure
states (N ¿d 2), which can be experimentally determined, without prior
knowledge of the state. We have proved that this measure has all the
properties expected of a ¡¥good¡| entanglement measure including the above
properties. We have computed this measure for important classes of N-qubit
states like GHZ states, W states and their superposition, as well as for
physical application like 1-D spin chain. We use this measure to follow
the entanglement dynamics of Grover¡|s quantum search algorithm. We hope
that this measure will prove to be useful in quantitative analysis of
entanglement in various applications.




***

LL11013E

Chromosomes meeting in the dark

At the onset of meiosis - the specialized cell division required
in sexual reproduction - homologous chromosomes in the cell nucleus
recognize each other at a distance and come in physical contact.
Such a step is crucial for preventing fertility problems, birth
defects and cancer. Yet, the mechanisms of self-recognition and
colocalization remain deeply mysterious.
In this paper, we propose a model describing how DNA binding
molecules guide the long distance interaction of special
chromosome sequences: if molecule concentration exceeds a critical
threshold, they induce a spontaneous recognition and colocalization
of chromosomes, otherwise independently diffusing. By acting on such
a switch, having a thermodynamic origin, the cell can actively
control pair formation and release.
The issue can have also a broader relevance as many other essential
cell processes involve the organization of chromosomes in nuclear
space. The new stochastic regulatory mechanism here described could
be important to those cases as well.


***

LQ11849

See the kinetics of self-assembly of molecules on surfaces

It has been well-known that ammonia molecules on Si surfaces are self-assembled. The self-assembly has been tentatively or rigorously from the quantum mechanical calculations considered as a result of the H-bond interaction between the molecules. However, the atomic structure of the molecules self-assembled on the surface has been highly controversial to the surface scientists; the H-bonded linear chain structure is the lowest in energy, but the zigzag chain structure is more preferential in experiments, which consists of surprisingly no H-bond. In this paper, we show explicitly that not only the H-bond but the covalent coordinate bond between the ammonia molecule and the surface Si atom plays an essential role in the self-assembly of the molecules. Surface chemical reactions on reactive surfaces are typically irreversible and thus easily form an in-equilibrium state. Therefore, searching for the low energy configuration sometimes conducts us to a wrong conclusion. In order to see the kinetics of the self-assembly, we investigated the detailed potential energy surfaces from first-principles, and the experimentally observed zigzag feature is found to be well described by the kinetics consideration.

CP10110
MAGNETIZED NEUTRON MATTER IN NEUTRON STARS


It has been long time thought that the presence of a very

intense magnetid field can induce changes in the properties

of neutron matter. This is mostly the composition of compact

objects like neutron stars. In our work we study what is the

change induced by strong magnetic fields up to a maximum

strength of $B=10^{18}$ Gauss (B on Earth is about 0.5 Gauss)

in the alignement of spins of the constituent neutrons in

this kind matter under extreme conditions. We study

differences arising when two possible parametrizations of

the nuclear interaction, Skyrme and Gogny forces, are

considered. We find that for moderate temperatures and for

both descriptions of the nuclear force, at low densities,

below 0.5 times saturation density (that of heavy nuclei on

earth), a large percentage of the nuclear spins orientate

along the direction of the magnetic field axes while they

remain below $12\%$ in the range 0.5 to 3 times saturation

density. At higher densities while Skyrme forces predict a

transition where all spins align along the magnetic field

axes Gogny force prevent this behaviour and keep it below $5\%$.

We find that additional changes are induced in the

composition, masses and energies of the plasma that may be

relevant to the internal structure of pulsars.


***

LN10977B

The reduction of oxide nanoislands on metal surfaces is found fundamentally different from bulk oxides. The reduction of metal oxides plays critical roles in many fields including materials science, microelectronics, and chemical applications. Traditionally, the reduction of metal oxides has been described using phenomenological kinetic models (e.g., “nucleation and growth model” and “interface model”) where the reduced oxide phase nucleates and grows on the parent oxide and the reaction rate depends either on the nucleation rate of new phase or on the interface area between the reduced phase and the parent oxide phase. Using in situ environmental transmission electron microscopy and atomic force microscopy, the authors have demonstrated that the reduction of Cu2O islands on Cu(100) surfaces is accompanied by the growth of the reduced phase (e.g., Cu) on the substrate surface surrounding the oxide islands rather than on the parent oxide; this is fundamentally different from the assumption by the phenomenological kinetic models. The reduction of these surface oxide islands by this mechanism results in the striking formation of surface craters, and their Monte Carlo simulations reveal that the growth of the crater rim is controlled by the homoepitaxial growth of Cu adatoms displaced from the reducing Cu2O islands.


***


BR10569

Electron motion in artificial polycrystals


How does a grain boundary modify the conductivity of an otherwise
crystalline material? S. Klinkhammer and coworkers have addressed this question by designing an artificial meta-lattice (also known as antidot lattice) containing well-defined grain boundaries. They find that the electrons tend to propagate better
along the grain boundaries than across them. Within a classical picture, the electrons adhere slightly to the grain boundary but can move around inside it. Moreover, this effect can be tuned by a magnetic field. The artificial lattices were generated by simulating the condensation of a gas of circular disks to a two-dimensional polycrystal with a lattice constant of about 0.6 micrometers.

This pattern was transferred by lithographic means into the electron gas of
a semiconductor heterostructure and investigated by transport experiments at
low temperatures.

The results are particularly relevant regarding emerging concepts based
self-assembly for the fabrication of functional metamaterials, in which domain formation is usually unavoidable.



***


BPR1059

This paper reports the discovery of an ultra-high temperature (1275
K) ferromagnetic-like transition in multiwalled carbon nanotube mats.
After vetting ferromagnetic interpretations and finding them
unsatisfactory, Zhao and Beeli find a natural interpretation based on
ultra-high temperature superconductivity. A little known
superconducting magnetic phenomenon is the paramagnetic Meissner
effect while better known is the diamagnetic Meissner effect. The
nano-sized magnetic impurities in the nanotube mat seed a
paramagnetic signal via the formation of an odd number of p junctions
in numerous loops composing the mat sample. Thus the iron magnetic
impurities used to seed the growth of the nanotubes symbiotically
interact with the ultrahigh temperature superconductivity to produce
the paramagnetic Meissner effect (orbital ferromagnetism) with the
onset temperature (1275 K) much higher than the Curie temperature
(about 1000 K) of the iron impurities. By considering a negligible
contribution of orbital diamagnetism at or above room temperature in
a magnetic field parallel to the tubes' axes, the authors
quantitatively interpret previously reported diamagnetic signals in
impurity-free samples as due to the more familiar diamagnetic
Meissner effect.

***

ln11264

*Capillary-like Fluctuations at the interface of a granular liquid. *

New experiments with granular jets (made of spherical glass beads) falling from a funnel shaped container show that capillary-like behavior known to place at the interface of liquid-gas can be observed on a macroscopic scale. The experiment was undertaken by Y. Amarouchene and his colleagues at the CPMOH University of Bordeaux1 (France). At the scale of a molecule, the free interface between any two fluids is not as smooth and mirror like as it appears on a macroscopic scale since thermal motion can easilly roughen the interface (whose interface roughness is given by a balance between thermal energy and capillarity). This give rise to waves that propagates at the interface. The same phenomenolgy seem to hold for granular fluids although thermal energy is irrelevant in this case. This opens the way to a better understanding of small scale interfacial phenomena in these widely spread materials.

5-28-08

BQ10747
Can laser light cool semiconductor devices?

Temperature reduction by suitable laser irradiation is a well
established technique for cooling free atoms and trapped ions. Extending
this technique to condensed matter has been an attractive goal ever
since the first experiments on atomic systems. Particularly
semiconductors would be an attractive target, where laser cooling might
provide vibration-free cooling. Laser cooling works by converting the
thermal energy of the material into optical energy: if the energy of the
laser photons is set below the energy of the photons that the device
emits, the system can combine the energy of the incident photon with
that of the lattice vibrations to generate a photon with higher energy
that is subsequently radiated away. In our paper we present for the
first time a detailed experimental study of this process (known as
photoluminescence up-conversion) in semiconductor nanostructures. In
particular, we determine the optimal choice of the laser wavelength as a
function of temperature. We find that the cooling power of a given laser
beam increases with temperature, in close analogy to conventional
cooling systems.


***

BN10462
Nanoparticles of cobaltites; intriguing and useful

When the size of the magnetic nanoparticles is reduced to few nanometers,
some of their basic magnetic properties are strongly influenced by the
particle size and may differ significantly from the bulk properties. As
the particle size decreases, the surface and interface effects become more
and more important. In our paper, we report magnetic and structural
properties of nanocrystalline LaCoO3 (cobaltites) with particle size
ranging from 25 to 38 nm. We found that with decreasing particle size the
unit cell expands substantially due to surface effects and the
ferromagnetic moment increases simultaneously with lattice expansion,
while the temperature Curie, Tc, remains nearly unchanged. Contrary to the
downsizing effect, we show that an applied pressure suppresses
dramatically the volume of FM phase leading to its full collapse at 10
kbar, whereas Tc does not change under pressure. The unique behavior
strongly suggests that the ferromagnetism in LaCoO3 is controlled by
unit-cell volume through a variation of Co-O bond length. Magnetic
nanoparticles may found technological applications in logic circuits,
magneto-electronic devices, magnetic data storage (a new higher speed
computer) and in biomedicine, e.g., new medical therapies (hyperthermia)
and as effective catalyst in chemical reactions.

***

EN10391

Heat engines convert the heat transferred from a hot body to a cold
body into some mechanical work, for example the lifting of a weight,
while heat pumps perform the opposite operation. According to
Classical Thermodynamics evaluation of the work W produced by a heat
engine per cycle, and its efficiency, requires the introduction of
absolute temperature and entropy. The latter quantity has been the
subject of many discussions and it is often found difficult to
comprehend. With the help of a mechanical equivalent of the quantum
heat engine, this paper provides a method of evaluation of the engine
efficiency that relies on only two elementary considerations. The
first one involves the potential energy of a weighting ball in the
gravitational field. The second is that the probability of picking up
a particular ball among a collection of N similar balls is equal to 1/
N. Thorough mixing of the balls is implied as for any (fair) lottery
machines. From the authors viewpoint, it is this element of chance
that distinguishes heat engines from more conventional mechanical
engines. In other words, by following the authors argument, most of
the classical thermodynamics laws may be understood with almost no
previous knowledge in physics. Negative temperatures (e.g., atomic
reservoirs with population inversion) and quantum heat engines may be
understood in the same manner.


***

BE10551

A new tricitical universality class

We have found a new tri-critical universality in the
anti-ferromagnetic classical XY model on the Kagom'e lattice
with easy-axes single-ion anisotropy. The Kagom'e lattice is a
two-dimensional network of corner-sharing triangles, in the
other way it's composed of three intervening triangular Bravais
lattices. The XY Kagom'e anti-ferromagnet is a prototype of
the systems representing a class fascinating phenomena called
magnetic frustration. The frustration refers to the presence of
degeneracy in the classical ground states arisen from
arrangement of spins on triangular units. It has been previously
found by I. Rittchey, P. Chandra, and P. Coleman (Phys. Rev. B 47, 15342 (1993)),
that this model shows only a Kosterlitz-Thouless transition in the absence of anisotropy,
which is a topological phase transition.
In our work, We added an easy-axes single-ion anisotropy to The
XY Kagom'e anti-ferromagnet, and studied its the critical
properties by employing an optimized Monte Carlo simulation. We
found that for large values of anisotropy, this system exhibits
an continuous transition to a so called all-in all-out state, in
which all the planar spins are located toward the easy-axes
directions from corner to center of the triangles or vise versa.
Since the large value of anisotropy limits the spin degrees of
freedom only along these directions, so this transition is in
Ising universality class. However the transition for small values
of anisotropy is dis-continuous, indicating the existence of a
tri-critical point for this model. The computed critical exponents
near this point, show deviation from those of 2d-$\phi^6$ model
which is, up to now, the only known two-dimensional tri-critical
universality class. We believe that transverse fluctuations
normal to easy-axes directions accompanying with the special
geometry of the Kagom'e lattice are responsible for this new
tri-critical behavior.



***

BR10618

Extremely low electron density with huge mobility revealed in Graphite

Graphite, the material inside your pens, starts to reveal its true
transport properties. Scientists from Germany, Spain and China,
developed an experimentally simple method to obtain basic properties of
the conduction electrons, like their average mean free path, density and
mobility without adjustable parameters. The method is based on the
change of resistance with a small constriction. Applying it to a piece
of oriented graphite, the team demonstrated that lowering temperature
conduction electrons in graphite can move several micrometers without
having scattering whereas their density tends practically to zero, which
can be translated in a huge mobility. According to the authors those
high mobility values are much larger than single graphene layers of
micrometer size can ever have. The results indicate that ballistic
electronics in graphite is possible and phenomena like
conduction-electron diffraction should be observable. Graphite
disconcerts even more when one realizes that its absolute resistivity is
as small as of a good metal. But how is it possible since there are no
electrons? Superconductivity is the authors' suggestion.

5-27-08

LP10931
Invisible waves shape continental slopes




Throughout the world, the ocean floor beyond the continental shelf
slopes at an average angle of 2 to 4 degrees, even though marine
sediments can stably pile up with slopes up to about 15 degrees. Zhang
et al. at the University of Texas at Austin have conducted laboratory
experiments that provide an explanation why the continental slopes are
at angles of only a few degrees. The scientists show that tidal flow,
back and forth along a sloping ocean floor, can generate strong internal
gravity waves, which are a type of wave that can form in fluids whose
density increases with depth, as in the oceans. Internal waves are
peculiar in that they travel only at a particular angle, which in the
oceans is set by the frequency of the tides and the variation of density
with depth. The experiments show that the waves near an ocean floor can
be very strong and can prevent deposition of sediments at larger angles,
thereby limiting the continental slopes to be at the angle of the
internal gravity waves.


Caption for VelField.jpg: Rapid flow (the dark red region) along a
sloping ocean floor, observed in a laboratory experiment where internal
gravity waves travel at the same angle as the slope of the ocean floor.

Caption for KH.jpg: The flow along the sloping ocean floor can become so
strong that the fluid rolls up into these patterns, called
Kelvin-Helmholtz billows.

***


LM11241

Images were stored in a gas of atoms for several micro-seconds



Quantum information can be coded in various physical realizations such as light pulses, internal quantum states of matter particles and more. Each realization has its unique benefits and drawbacks, for examples light pulses are ideal for long-distance communication, but are hard to manipulate. Therefore, in the last years several methods to coherently convert quantum information from light pulses to matter excitations and vice versa were explored. In this work we demonstrate a technique to map an image onto a gas of room temperature atoms, utilizing a phenomenon called electromagnetically induced transparency. All the information in the light field, including both its amplitude and phase patterns, is converted into the internal quantum states of the atoms, and transferred back to an image after several micro-seconds. We further explore a technique to immune the images from blurring due to the thermal motion of the atoms, by applying a suitable phase coding to the image. This technique, which is the atomic equivalent of a resolution-enhancement method used in optical lithography, dramatically improves the visibility of the image for long storage durations (see figure). Storing images in a gas of atoms might have future applications in quantum information and all-optical image processing and manipulation.

***

LM11731

From order to disorder when mild impurities hold back

How a system evolves from an ordered to a disordered state (or the opposite), while mild impurities hold back, is a long standing question that has been addressed in different complex systems. We have studied particularly an array of quantized magnetic flux lines in a low Tc superconductor (NbSe2, Tc ~ 7 K) as it transformed from an ordered triangular low temperature lattice to a disordered high temperature configuration in the presence of mild random defects. An advantage of this model system is that by “shaking” the flux lines with an alternating magnetic field at different temperatures, the corresponding stable state is accessed. It is known that the compression modulus of the array varies with the degree of order, so a very sensitive magnetic measuring system was used to determine the elastic response at each temperature, assuring that the array was not modified by the measurement itself. We conclude that in a small temperature interval (of about 0.1 K) while the system goes from order to disorder (or back) , the equilibrium states are a mixture of fully ordered and fully disordered regions, the proportion of which changes across the transition, suggesting that this phenomenology could also occur in colloids, Wigner crystals, charge density waves, etc.

***

LL11135

Save the Notion of Spin for Photons and Gluons

A particle's spin is an important information carrier, and is the
basis for quantum communication and quantum computation. But rather
disturbingly, for many decades physicists are unable to define the
spin properly for photons and gluons. The difficulty is due to a
kind of arbitrariness in physics: the gauge freedom. In the
traditional definition, the spin of photos and gluons depends on the
choice of gauge, and since one is free to change the gauge, such
definition has no concrete physical meaning. In this work, we
succeed in identifying the physical components of photons and gluons
which are unaffected when changing the gauge. With these physical
components, the spin of photons and gluons can be defined
concretely. This saves the notion of spin for photons and gluons,
and allows physicists to properly manipulate the photo spin in
quantum communication, and meaningfully investigate the total amount
of gluon spin inside the nucleon --- a key issue in understanding
where the nucleon obtains its spin.

***


LP10889

New mechanism for a single molecule switch with the negative differential
resistance (NDR) feature is discovered--NDR that constitutes rise and fall
in current with increase in applied voltage is used to build switches for
computers. To continue drive towards miniaturization, ultra-small single
molecule NDR switches are essential. Even after a decade of its first
realization, this device is not yet operational. The reason is that
various groups have proposed contentious mechanisms to explain the origin
of NDR in single molecule device. Unless the origin of NDR is underpinned
resolving one of the greatest nano-debate of this decade, a reliable
device cannot be made.

In this letter, we have unified two distinct dimensions of this debate,
role of junction and the molecule itself, into a single framework.
Specifically, we have found that the ten years long debate was due to
overlooking a well-known phenomenon in non-equilibrium physics. We have
unambiguously shown that the ¿symmetry breaking and appearance of a new
broken symmetry phase in the electronic state¿ of the molecule upon
increasing applied bias is the root cause of NDR. This could be used as a
universal recipe to design single molecule switch for the new generation
molecular computer.


***

LM11414

Temperature can switch the coupling between magnetic layers.

Magnetic thin films coupled through layers of nonmagnetic materials
are at the heart of modern reading devices of magnetic information
in hard disks. The Nobel Price 2007 was awarded to P. Grünberg and
A. Fert for the discovery of the "giant magnetoresistance" in these
layered systems: A strong reduction of the electrical resistance when
an applied external magnetic field changes the relative magnetization
direction of the magnetic layers from antiparallel (antiferromagnetic
coupling) to parallel (ferromagnetic coupling). In the absence of
external field, the coupling strength between the magnetic layers is
known to depend in an oscillatory way on the thickness of the nonmagnetic
spacer layer, changing from ferromagnetic to antiferromagnetic coupling.
In this work, we have grown trilayers of two different magnetic
rare-earth metals (Gd and Tb) separated by a nonmagnetic Y layer.
We found, besides the expected oscillatory dependence of the magnetic
coupling on the Y-spacer layer thickness, a novel temperature-dependent
phase shift of the oscillations. This strong temperature dependence even
leads to sign reversals between ferromagnetic and antiferromagnetic
coupling for constant Y-thicknesses. Results are interpreted in terms of
magnetization-induced changes in the reflectivity of conduction electrons
at the magnetic-nonmagnetic interfaces.

***


LP11610

Increasing thermoelectric efficiency: A dynamical systems approach

POWERFUL HEAT

In our paper we present a mechanism for a drastic increase of efficiency of
thermoelectric power conversion which - if implemented - may lead to
environmentally benign and economically competitive refrigerators and heat
engines. Providing a sustainable supply of energy to the world's population
will become a major problem as fossil fuel supplies decrease and world demand
increases. Also there is an increasing environmental concern about waste heat,
and about chlorofluorcarbons used in most compressor based refrigerators. It
is therefore expected that thermoelectric phenomena, which involve conversion
between thermal and electrical energy, will play an increasingly important
role in meeting the energy challenges of the future. The difficulty is that,
so far, thermoelectric power generators and refrigerators have poor
efficiency. The latter depend on a pure number, the so-called figure-of-merit
ZT of their material components. In spite of the efforts of the last five
decades, the values of ZT remained around one, while a value larger than 3
will make thermoelectric refrigerators economically competitive with the
conventional home refrigerators. In our paper, using an approach from
nonlinear dynamics and chaos, we have discovered a general microscopic
mechanism for an unlimited increase of the thermoelectric figure-of-merit ZT,
thus allowing efficiency to approach the Carnot's limit of an ideal engine.
Our results are demonstrated by a simple numerical calculation on a Lorenz gas
type system.

***


LR10990
Ultrasensitive detection of lowest H2D+ rotational transition

The lowest rotational transition of one of the most important
astrophysical molecules, H2D+, has been observed in the laboratory for
the first time. This result will trigger an astronomical search using
new and upcoming telescopes, like APEX and SOFIA.
In the experiment, only a few hundred of the ionic species are stored in
a low-temperature ion trap and excited by a THz-beam with very high
spectral purity. Using the small energy amount gained by absorbing
THz-photons,
the ions undergo a chemical reaction and the products are detected
with high sensitivity. This is the first example of pure rotational
spectroscopy of molecular ions using this novel technique.
The astronomical observation of this transition based on the present
laboratory work will have far reaching consequences, including the
determination of the coldest temperatures in space and the ortho to para
ratio of molecular hydrogen, the most abundant molecule in the universe.
Unravelling the pivotal role of these two nuclear spin configurations of
hydrogen will finally give a hint to how water came to earth and whether
life was kick-started from space.

***


LM11170

Ultrashort light pulses weld ultracold atoms together

At temperatures close to absolute zero, matter can be controlled in a way that is very different from our every-day perception. Ultrashort pulses of laser radiation, just like those used, for example, as a precision knife in laser eye surgery, have been employed by a collaboration of researchers from the Universities of Freiburg and Berlin to weld atoms in an ultracold gas together into molecules. An advantage of this method of making molecules is that the resulting molecules remain as cool as the atoms from which they are made. The researchers prove the existence of the molecules by firing in a second ultrashort light pulse a short time after the first one. In addition to the laser light creating molecules, it was surprisingly found that the formed molecules interact further with the laser field. The molecules take electromagnetic energy from the laser field and store it internally for a short time before giving it back to the laser field. This coherent process is repeate
d on a time-scale that depends on the laser frequency and the binding strength of the molecules. The observations are perfectly described by full quantum-mechanical calculations. With this work, the combining of the ultracold and the ultrashort worlds has become reality, and new possibilities for the quantum control of atoms and molecules near absolute zero temperature, where quantum mechanics governs the dynamics, have come within reach.

5-19-08

LF11381

Does the size really matter?

It is well known that dynamics of atoms in nanocrystalline materials is remarkably different from their bulk counterparts. The anomalous features are usually attributed to small nanograins with enhanced surface-to-volume ratio. To further reveal the origin of those anomalies we investigated the atomic dynamics of nanocrystalline Fe90Zr7B3 alloy at various phases of crystallization. The atomic vibrations of the nanograins were separated from those of the interfaces for a wide range of grain size and interface thickness. Surprisingly, the results show that the atomic vibrations of the nanograins do not vary with their size even down to 2 nm, and still closely resemble those of the bulk. The known vibrational anomalies originate from the interface atoms and the degree of deviation from bulk dynamics is proportional to the interface fraction.
A practical implication of these results is that in order to optimize particular thermodynamic properties of the nanocrystalline materials one has to control precisely the fraction of the interfaces rather than the size of the nanograins.

***

LM11721

Galactic magnetic fields could originate at the epoch of reheating after inflation


The origin of the microgauss magnetic fields observed in galaxies and clusters
of galaxies is still a mystery. In this paper we propose that they could be produced
at the electroweak transition after a period of low-scale hybrid inflation. We show
how the non-equilibrium processes occurring at the epoch of reheating of the
Universe may give rise to a significant fraction of energy density in the form of
helical magnetic field lines, whose correlation length grows via inverse cascade
in the primordial plasma. These magnetic fields would be seen today in galaxies
and clusters of galaxies, but not in the cosmic microwave background. The
detection of a helical component of cosmological magnetic fields would give yet
another signature, together with the predicted Gravitational Wave Background,
of the violent processes occurring at the Big Bang.

***


LQ11037
Active cooling of massive objects

Several groups worldwide are investigating the possibility of cooling macroscopic mechanical resonators towards the quantum mechanical ground state, using active feedback or laser cooling techniques. A possible outcome of this research could be the observation of quantum behaviour in a macroscopic object. In this paper, we demonstrate that these techniques can be efficiently applied to resonators much more massive than previously analysed systems. In particular, we cooled the resonant modes of the cryogenic gravitational wave detector AURIGA, a 2 ton aluminium bar resonator whose motion is detected by a very sensitive SQUID-based position sensor. Starting from a temperature of 4.2 K, we were able to achieve by active feedback a minimum equivalent temperature of 0.17 mK, which is even lower than the temperature previously reported for much smaller systems. This experiment suggests that, using this technique, it could be possible to cool even massive human-scale resonators towards the quantum ground state.

***

LQ11568
QUANTUM MOTION SOLVED ON CURVED SURFACES WITH ELECTRIC AND MAGNETIC FIELDS

We derive the quantum dynamical equation for a charged particle moving on a curved surface in the presence of an electric and magnetic field.

It is evident that both the geometry of the surface and the applied fields influence the motion of a particle, but, up to now, it was not clear if these factors couple with each other.
We find that it is not the case: the effect of the fields is independent from the surface curvature.
In addition, we demonstrate that, also with fields, the motion of the particle on the surface is not affected by the dynamics along the direction perpendicular to it.

Applying our results, it has been possible to obtain the quantum equation of motion on surfaces of frontier interest for nanosciences, such as spheres, cylinders and tori.

Our new equation will be useful both for the interpretation of experimental results and theoretical predictions involving curved structures immersed in fields, for example in the analysis of new effects in low-dimensional nanostrucures.

The results are the outcome of the collaboration between two young researchers, a solid-state physicist and a field-theorist: this is a proof of how fruitful is the interplay of competences among different areas of physics.

***

LM11290
Probing colored light and ghosts by gentle warming

Sometimes victory of a long-distance racer depends on what is usually
considered to be not a even a physical issue. This is the strength of
the racer's spirit. The colored gluons and quarks -- basic building
blocks of the theory of strong interactions -- emerge naturally with
other objects, ghosts. We demonstrate that the long-distance
propagation of warmed gluons is intimately related to proliferation of
the ghosts. The gluons are massless intensity of the colored "light" of
gluons created by a static quarks falls off as the inverse square of
the distance from the source. The same as for ordinary light. Color is
seen however only at short distances, less than about one femtometer
(one quadrillionth of a meter, 10^{-15}). At long distances only
colorless hadrons, or bound states of quarks and gluons are
observed. This phenomenon is known as color confinement.
In our work we show theoretically that slightly warmed gluons
and ghosts offer a new kind of conspiracy implied by confinement
of color. We demonstrate that the warm colored ghosts propagate
for long distances and the falloff of the intensity of the ghosts
and gluons obeys a certain relation.

***

LN11310
Electronegativity Identification of Novel Superhard Materials

The hardness of materials can be identified via electronegativity. The search for superhard materials is a huge challenge to scientists. Furthermore, people are also facing many new challenges to precisely measure the hardness of synthesized superhard materials. In this letter, the nature of hardness is systematically studied from the viewpoint of electronegativity, one of the most widely used parameters in chemistry, physics and materials science. We find that materials hardness is essentially determined by the electron-holding energy of constituent bonds per unit volume. The hardness of various materials can be satisfactorily predicted solely in terms of electronegativity and crystal structure. A number of bonds which can or cannot form a superhard material are qualitatively distinguished. Our work provides a new approach to design novel superhard materials from the general viewpoint of electronegativity, which will inspire people to further explore new superhard materials.


***

LP11122


"Quantum bit measurement reaches computing regime"

Very precise state measurements necessary to create a working Quantum Computer (QC) have recently been achieved in the lab. The QC uses information encoded in quantum bits ("qubits") which can exist in a quantum "superposition" of the states 0 and 1, in contrast to conventional bits which can only be in one of these states at any time. If built, the QC could exploit the quantum phenomena of superposition and "entanglement" to solve certain problems that are intractable on any conceivable conventional machine. To make an error-free computation, the state of most of the qubits in the computer must be read out with very high accuracy both during the computational process and to determine the final answer. This paper reports the high fidelity measurement of qubits stored in a single trapped Calcium atom. The state of the atom was repeatedly measured with a mistake occurring less than once in every 10000 tests. This 99.99% fidelity is high enough for a working QC and is believed to be currently the best measurement of any physical qubit. This achievement is particularly exciting given recent insights into the power of quantum measurement, which can be the driving force at the very heart of a quantum algorithm.

***

LL11113
ITER operational regime in a simple small experiment

The ITER experiment is now being built in Cadarache, France, with the goal of showing the feasibility of producing controlled thermonuclear fusion energy. Its success will critically depend on reaching an operational regime where matter and heat are highly confined, the so called H-mode regime. Although the discovery of such a high confinement regime dates back to the '80s, the underlying physical mechanisms have not been fully understood yet. In particular, the fact that the H mode is achieved only in big fusion-relevant devices has made its dynamics always very difficult to diagnose and control. In the present paper, a theoretical prediction is made that an H mode-like regime can also be achieved in a simpler and smaller sized device with easy diagnostics access. The relative simplicity of the considered configuration has allowed the theoretical exploration of the properties of this operational regime in great detail.

***


LM11031

Calcium as the Superior Coating Metal in Functionalization of Carbon Fullerenes
for High-Capacity Hydrogen Storage

There has been an expanding effort of the scientific community searching
for the most promising materials for high-capacity hydrogen storage,
with carbon-based nanostructures representing one important class of
systems under intensive study. Because molecular hydrogen and pristine
carbon nanostructures such as fullerenes or nanotubes are both
sufficiently stable and relatively inert, a variety of surface
modification schemes have been proposed in the recent literature to
enhance the binding of molecular hydrogen, such as by doping (Ref. A),
coating (Refs. B and C, D), or charging (Ref. E), but each scheme having
severe limitations or running into disappointments. Our paper shows that
Ca as a coating element satisfies all the requirements to functionalize
fullerenes (and related carbon nanostructures) as potential high storage
media. Even more pleasantly, Ca turns out to be (probably) the only
coating element in the periodic table to deliver the desired
functionality, making this contribution truly refreshing in an otherwise
somewhat frustrated community.

The attached figure shows that the optimized organometallic complex of
Ca32C60 can contains 92 H2, which corresponds to a hydrogen uptake of
8.4wt%.

5-13-08

LG11494

Unraveling the mysteries of how complex liquids flow

Simple fluids, such as water or oil, flow in response to applied forces that are well understood and described using a set of coupled differential equations, known as the Navier-Stokes' equations. An important parameter for these fluids is the viscosity, which describes the friction between the molecules and thus their resistance to flow. However many materials in everyday life that flow are composed of small particles, such as powders or grains, which may be inside a liquid, such as pastes or emulsions. For these materials the friction between particles is very different from that of molecules in simple fluids, and consequently their resistance to flow cannot be described with a hydrodynamic viscosity. Nonetheless researchers are hard at work trying to extend the hydrodynamic descriptions that work well for simple fluids to these complex fluids. Aqueous foams are an appealing model system for a complex fluid, because their composition is elementary: they are merely composed of packed bubbles surrounded fluid. In their recent experiment study, Rheology of steady-state, draining foams, Soller and Koehler find that the friction of sheared bubbles in a foam is inversely proportional to the thickness of the films separating bubbles. Wetter foams with higher liquid content have thicker films, allowing bubbles to slide past each other more easily than drier foams where the films are thinner. It still remains to be understood how friction changes with the shear rate; observations show that foams are shear-thinning and the their composition also affects the friction. Once the shear rate dependence is understood, a hydrodynamic description for foam flow should be possible that may lead the way to hydrodynamic descriptions of other complex fluids such as granular matter.

***

LN11547
A universe in turmoil

A key open question in our understanding of the universe is the
quantum nature of the big bang -- its earliest moment which general
relativity can only describe as an infinitely dense singularity. In
this letter, detailed considerations of quantum cosmology show that
the density of the universe, even when it emerges at the big bang,
must respect a universal upper bound no matter how much it quantum
jumps and fluctuates. The precise form of how the universe starts its
expansion turns out to be dictated by another quantum parameter called
correlation (or squeezing). When we picture the early history of the
universe, we usually think of a steadily expanding tube emerging from
a hot, narrow phase at the big bang. Its initial extension was far
from smooth but quantum and in wildly fluctuating turmoil. The new
results put this phase under high control and restrict the options of
what precisely happened before the big bang: The universe either
sharply bounced back after a long collapse, or it emerged as the
sudden liberation out of a long phase of imprisonment in the quantum
world.

***


LN11566

Millikan's experiment in a liquid

The experiment of Robert Millikan in which the elementary charge is
determined from the motion of charged oil drops in air has been
repeated many times, either to find a more precise value of the
elementary charge, or because it is such a simple and elegant way to
measure a physical constant. In this paper it is revealed for the
first time that the charge of micrometer-sized colloidal particles
suspended in a nonpolar liquid comes in multiples of the elementary
charge. In the experiments, the motion of the particles under
influence of an electric field is measured by microscopic particle
tracking. The particle mobility ?the speed divided by the electric
field strength? changes with a fixed step, if the charge on the
particle is modified by plus or minus one elementary charge. From
detailed mobility measurements on a single particle over many seconds,
the number of elementary charges on the particle can be determined as
a function of time. In addition precise values are found for the
particle size or (if the size is known) for the elementary charge. The
experiment can be seen as the colloid variant of Millikan?s
experiment, but is a bigger challenge due to the higher viscosity of
liquids compared to air. The experiments can be used to characterize
properties and charging mechanisms in all kinds of colloids.

***

LP11079

Wisconsin Researchers Put a New Spin on Decoherence

It is exceedingly difficult to construct bits for a quantum computer (“qubits”). Even minute amounts of noise are sufficient to destroy coherence – the essential quantum nature of the qubit. In the case of qubits based on superconducting circuits, a dominant source of decoherence is a low-frequency magnetic flux noise whose existence has been known for over 20 years, but whose origins were never explained. Now researchers at the University of Wisconsin, Madison have uncovered clear evidence for a high density of unpaired electron spin magnetic moments on the surfaces of the superconducting thin films that are used to make qubits and other sensitive superconducting detectors, including Superconducting QUantum Interference Devices (SQUIDs). Fluctuations of these moments account for the previously unexplained low-frequency flux noise, and for its apparently “universal” character: the noise is only weakly dependent on a wide range of parameters, including superconducting materi
als, the scale of the device, and temperature. This research suggests that optimization of the surfaces of the superconducting thin films could lead to detectors with improved noise performance, and to superconducting qubits with improved coherence times.


***

LN11156

“Mixed solids” of nanoparticles

Most of useful materials are mixed crystalline solids composed from different atoms (eg. stainless, permalloy, etc.). The semiconductor and metal nanoparticles are one of nanoscale building blocks for tailored materials with fascinating and multifunctional properties beyond isolated nanostructured materials. It is expected that the close-packed mixed solids composed of semiconductor and metal nanoparticles make it possible to realize novel optical and electronic properties; semiconductor nanocrystals exhibit size-dependent luminescence with high-quantum yields, while metal nanoparticles exhibit large electric-field enhancement due to the surface-plasmon excitation. In this Letter, Kanemitsu and coworkers successfully fabricated “mixed solids” films composed of semiconductor and metal nanoparticles using a very simple technique and revealed their ultrafast energy flow mechanism from the semiconductor and metal nanoparticles on the nanoscale. This is a
first step toward the future material engineering using “mixed solids” composed of nanoparticles and will contribute to development of novel functionalities in the artificial mixed solids.

5-7-08

LP10816
How fast will materials break as they get tired?


The so-called "fatigue" phenomenon, responsible for the mechanical
failure of structural components when exposed to periodic loading even
if the load amplitude is much below the safety limit, has been largely
recognized in engineering and physics as a very important
technological problem with many involved scientific challenges. For
instance, this subcritical process, which gradually leads to failure
due to macroscopic fractures, typically occurs unexpectedly and has
been responsible for a large number of airplane and railway crashes
with considerable human loss. A crucial dynamical feature of this
fatigue phenomenon is expressed by the empirical "law of Paris", which
states that the growth rate of a crack increases as a power-law of the
instantaneous crack size, with an exponent that is strongly material
dependent. In our study, we have been able to derive analytically and
confirm numerically the connection between the exponent in Paris' law
and the exponent of a damage accumulation mechanism at the microlevel.
To our big surprise, we discovered that there is a "critical" value
for the damage accumulation exponent which separates two very
different regimes of crack growth. In addition, we also studied the
role of disorder (the presence of impurities, for instance) and found
again that this critical point is expected to have the most striking
consequences on crack growth rate, namely that disorder is relevant
below it and irrelevant above it. Our results can have far-reaching
consequences in the understanding and control of subcritical crack
propagation. On one hand the discovered relation between the damage
and the Paris exponents, which in principle could be checked
experimentally, could help to predict lifetimes of samples by studying
the velocity of small cracks. Finally, it is important to mention that
since the microscopic exponent of the damage accumulation law is
material dependent, it could play a central role in the engineering
design to increase the robustness and optimize the mechanical
performance of materials.

***

LN11036


EVEN BLACK HOLES CANNOT HIDE INFORMATION


Black holes form by gobbling up matter. According to Einstein's
general relativity, information contained in the matter is lost
forever. However, in 1974 Hawking discovered that black holes are
like black bodies and they radiate quantum mechanically. As a
result, matter does eventually come out, but it emerges as thermal
radiation which has no memory of how the black hole was formed.
So, it appeared that this information is still lost in spite
of the evaporation process. But this conflicts with a basic tenet of
quantum mechanics. Thus, gravity seemed to make the amazing demand
that the mathematical structure of quantum mechanics itself must
be modified. Since quantum mechanics is the most successful physical
theory we have, the issue of information loss has drawn
much attention over the last thirty years and is widely regarded
as one of the most fundamental problems in theoretical physics.

In recent years, string theorists have appealed to the so-called
AdS/CFT conjecture to argue that information is not lost and
quantum mechanics can remain in tact. However, these arguments
have not been able to explain how the information comes out of
black holes. In the forthcoming PRL, Ashtekar, Tavares and
Varadarajan use quantum gravity to provide a space-time
description of this process for 2-dimensional black holes. These
black holes are technically simpler to work with but are
conceptually very similar to spherical black holes in
4-dimensions. They argue that quantum effects of geometry resolves
the black hole singularity and significantly extend space-time.
Hawking's thermal radiation is an excellent approximation but only
at early times. The apparently lost information emerges at late
times in the extended quantum space-time. Thus, because quantum
space-time does not end at a singularity, it has ample room in the
distant future for the information to reappear.


***

LB11631

Lasing, normally thought to require population inversion is shown to be possible even without population inversion. We show that atomic population undergoes an interesting capitalistic (rich gets richer) behavior, which can be taken as a definitive signature of lasing without inversion.

Einstein's explanation of the stimulated emission has given rise to the devices we now call lasers. To obtain laser light, the medium (atomic or molecular) need to be excited as a condition known as population inversion is to be satisfied. Population inversion means the higher energy states need to be more populated than lower energy states, which makes it very difficult to obtain lasing in the high frequency region of the electromagnetic spectrum. This requirement gets modified if there is an extra transition coupling with the lasing transition. The quantum interference between coupled transitions makes population inversion unnecessary for lasing. However, there are other competing processes and pure LWI contribution is difficult to discern. Dr. Kapale's work with Dr. Kilin and Dr. Scully shows how to extract pure lasing without inversion contribution and show an accompanying capitalistic effect in the population dynamics. An initially more populated ground state gets more populated with time; such behavior is a definitive signature of LWI. The concept of LWI is the only hope to obtain highly efficient X-ray or gamma-ray lasers. Also in the context of quantum information generation of pure states as initial states of the quantum system is a necessity and the capitalistic population dynamics proposed can be used to generate such pure states.

***

EP10430

Listening to singing bubbles

On volcanoes, giant gas bubbles exploding at the top of vents or at the surface of lava lakes generate acoustic signals. Thus, motivated by the potential applications in geophysics, we listen to bubbles bursting at the free surface of a complex fluid. We identify the basic mechanisms at stake in the sound generation. In the laboratory, a diluted hair-gel solution mimics the complex properties of lava, such as its peculiar mechanical behavior: if squeezed gently, it behaves as an elastic solid; if squeezed harder, it flows as a liquid. Due to these complex properties, the bubbles are elongated, and thus, behave as panpipes at bursting. The acoustic signal associated with one event exhibits a well-defined frequency, directly linked to the bubble length. The bubble geometry can be inferred from the spectral content. By contrast, the sound intensity is not only controlled by the bubble geometry but also strongly depends on the bursting dynamics. Consequently, the total amount of energy released by the explosions cannot be deduced from the acoustic energy recorded on the field.

***

ln11264

*Capillary-like Fluctuations at the interface of a granular liquid. *
New experiments with granular jets (made of spherical glass beads)
falling from a funnel shaped container show that capillary-like behavior
known to place at the interface of liquid-gas can be observed on a
macroscopic scale. The experiment was undertaken by Y. Amarouchene and
his colleagues at the CPMOH University of Bordeaux1 (France). At the
scale of a molecule, the free interface between any two fluids is not as
smooth and mirror like as it appears on a macroscopic scale since
thermal motion can easilly roughen the interface (whose interface
roughness is given by a balance between thermal energy and capillarity).
This give rise to waves that propagates at the interface. The same
phenomenolgy seem to hold for granular fluids although thermal energy is
irrelevant in this case. This opens the way to a better understanding of
small scale interfacial phenomena in these widely spread materials.


***

LM11565

Experimental evidence of 2He decay from 18Ne excited states


Two-proton cluster radioactivity in nuclei near the proton drip-line was theoretically predicted about 50 years ago as result of the pairing force. Although few cases were already observed, the reported experiments were either not able to distinguish between the true diproton (2He) emission and the uncorrelated emission of the two protons or suggested the latter as the decay mechanism.

A technique for disentangling the two decay modes was proposed in 1961 and in this paper was successfully applied for the first time to the two-proton decay from 18Ne excited states, demonstrating the existence of di-proton radioactivity.

The 18Ne nucleus, produced as radioactive beam through 20Ne fragmentation and subsequent in flight separation was excited via Coulomb excitation on a Pb target. A complex detection system allowed to identify on an event-by-event basis the charge, mass, energy and angle of each fragment produced in the interaction.

The novelty of this work lies in the analysis of the relative angle and momentum spectra of the two emitted protons which allowed to disentangle the uncorrelated (69%) from diproton (31%) emission and infer the relative branching ratios.

This finding will put new constraints on the description of nuclei near the proton drip-line important to understand the nucleosynthesis rp-process.

***


LP10807
Two-photon nonlinearity with many-atom cavity system
- Photons squabble over only "one chair" in the presence of many chairs -

If the two of you squabble over only one chair in a tiny room, the interaction
between the two should be strong. If many chairs are prepared for you, in
contrast, you do not have to interact each other. Similarly, two
photons--particles of light--interact each other most strongly if they are
confined in a cavity with only one atom. This is a key phenomenon and
currently a crucial subject in order to realize a quantum logic gate for
quantum information technologies. However, if many atoms are inside the cavity,
which is an inevitable situation in the implementation of solid-state devices,
interaction between photons easily vanishes. In this paper, we find a new
scheme to drastically change this standard scenario; the photons' interaction
is strongly enhanced even for a many-atom system. In this mechanism, many atoms
in a cavity are superposed, and this strange collective state behaves as if
there is only one chair under a particular design of many-atom cavity system.
This finding develops a new research field of the multi-particle cavity quantum
electrodynamics, and more importantly, it opens the link between the concept
of the quantum logic gate with an ideal model and the real-world solid-state
device technology.

***

LQ11684
The Potential of Graphene Nanoribbons for Nano-electronics

Graphene, a monolayer of carbon atoms tightly packed into a two-dimensional honeycomb lattice, has been suggested as a promising candidate for nano-electronics due to high carrier mobility in large sheets of graphene. Recently it has been demonstrated that very narrow (<10nm) graphene nanoribbons (GNRs) were semiconductors with adequate bandgap for transistor operation (Science 319, 1229 (2008)). The present work reported the highest-performance sub-10nm GNR transistors, with on state current density similar to small diameter carbon nanotubes (CNTs). However, a key advantage of sub-10nm GNRs over CNTs is that GNRs are all semiconductors without metallic species. The study suggests that the intrinsic properties such as electron mobility in narrow GNRs are limited by the scattering by the edges and may still have room to improve. Thus, all-semiconducting, high current sub-10nm GNRs are possible for future electronics beyond silicon.

***

LL11068

Non-locality fundamental for nano-scale fluids

What is it about the world of the very small that makes it so different to
the everyday world that we can directly experience? The standard answer to
this is quantum mechanics, where non-local phenomena dominate. However,
researchers from Swinburne University and RMIT University in Melbourne
Australia have shown that non-local phenomena are also of critical
importance for nano-scale systems that behave purely classically. They
simulated a system of inert atoms in the liquid state that are affected by
an external spatially dependent oscillatory force. The force generates a
shear stress in the fluid that can be computed exactly. This computed stress
was then compared to the stress predicted by Newton¹s law of viscosity,
which states that it should be directly proportional to the local velocity
gradient of the fluid, the constant of proportionality being the standard
shear viscosity. However, when the variation in the velocity gradient varied
significantly over a few atomic diameters Newton¹s law was shown to break
down dramatically. Using an expression that relates the stress to a
convolution of a non-local viscosity kernel and the velocity gradient over
all space, the team was able to predict the stress exactly. It turns out
that exact predictions of the flux of any fluid property under such extreme
conditions requires the use of non-local constitutive equations that relate
this flux to its conjugate thermodynamic driving force. This in fact is a
central feature of generalised hydrodynamics, which until now had not been
demonstrated so directly. Conditions where rapid variations in velocity
gradient occur on the order of atomic dimensions are to be expected in a
range of phenomena such as shock waves, shear banding and nano-fluidics,
which is where this work could be expected to have greatest significance.


***


Possible explanation of the breakdown of a fundamental symmetry in the
cuprate superconductors


In Phys. Rev. Lett. 100, 127002 (2008),
Kapitulnik's group at Stanford University experimentally
demonstrated that time reversal invariance, one of the fundamental
symmetries of nature, spontaneously breaks down in a class of high
transition temperature cuprate superconductors. In LL11262, a group of
theoretical physicists in the University of Maryland, Collge Park, gave
convincing arguments that the breakdown of this fundamental symmetry
could be due to local bond currents, also proposed to be spontaneously
generated, in these materials. The breakdown of time reversal
invariance and the state with spontaneous local currents may
ultimately provide important clues to the origin of the
anomalously high transition temperature of the cuprate
superconductors.

***


LM11356

Multi-Energy Anomalous Diffuse Scattering

Although characteristic properties of
many substances are related to the short-range
arrangement of atoms, a general-purpose method of
providing reliable information on local atomic
deviations from the average structure is still
missing. In this article, a novel x-ray method of
multi-energy anomalous diffuse scattering (MADS)
for imaging substances with atomic resolution is introduced.
MADS makes possible to reconstruct
numerically local atomic structures using the
measured intensities of x-ray diffuse scattering
from the sample. The method was tested using a
strontium titanate single crystal with
outstanding results. A sample volume with a
dimension of tens of ångstrøms was successfully
reconstructed. Images of several thousands of
atoms, including the light oxygen atoms, were
obtained (see Figure). Application of this method
to the imaging of local structures in both
crystalline and non-crystalline solids seems to be very promising.

***

LK10874
Manipulation of a cloud of a large number of antiprotons

We have succeeded in controlling the radial distribution of a single
component antiproton cloud (consisting of about one million
antiprotons) in a strong magnetic field by applying a rotating
electric field.
The rotating field was believed to be effective when some cooling
mechanisms were available, but the compression here was realized
under ultra high vacuum conditions.

The success of the active control on a large number of antiprotons is
an important step for a controlled synthesis of a point source of
antihydrogen atoms.

It also enables to prepare intense monoenergetic beams of ultraslow
antiprotons in eV ranges for the first time, which is practically
three orders of magnitude lower in energy than ever realized.

One can now study various collision dynamics involving "heavy" electrons
(i.e., antiprotons) such as antiprotonic atom formation and ionization
processes under single collision conditions.

***

LM10936
A fresh view on the classical problem of Poincare recurrences: how an
invariant fractal set governs the long-time recurrences in chaotic
systems.

While studying the stability of the solar system, Poincare noted a
remarkable property: unless planets collide or escape, they will
return to their initial configuration some time in the future. Later,
his famous recurrence theorem, published in 1892, played a central
role in the debate over the foundation of non-equilibrium statistical
mechanics: while Zermelo emphasized the formal contradiction between
recurrences and the irreversibility of macroscopic processes,
Boltzmann argued that the average recurrence time in macroscopic
systems is huge and therefore irrelevant in practice. This is no
longer true for low-dimensional systems, and recurrence is currently a
fundamental tool in the theory of dynamical systems. In this paper
we bring a new insight to this problem by considering an analogy to a
problem of escape in an open system. We find that the recurrence time
distribution is governed by an invariant fractal set, called chaotic
saddle, and the exponent governing its decay coincides with a
characteristic number of the chaotic saddle, its escape rate. In
typical Hamiltonian systems, as those considered by Poincare, we find
that this saddle can be effectively split in a hyperbolic and a
non-hyperbolic component that are responsible, respectively, for an
intermediate time exponential and asymptotic power-law decay of the
recurrence time distribution.