MAGNETIC RESONANCE IMAGING OF HEAVY QUASIPARTICLES IN METALS.
It has been known for some time that the conduction electrons in
certain intermetallic compounds containing magnetic rare earth
elements such as cerium appear to be hundreds of times more massive
than a usual electron. The increase in mass is comes from a coherent
quantum mechanical mixing of the localized f-electrons (of infinite
mass, so to speak) of cerium, say, with the conduction electrons: at
the Fermi level only a small percentage of “light” electrons is mixed
in, giving rise to massive quasiparticles - the so-called “heavy
fermions”. They carry a magnetic moment, or spin, that can be detected
in a magnetic resonance experiment: The sample is put in a static
magnetic field, which causes the moments to precess. An additional
high-frequency electromagnetic field is absorbed, when its frequency
coincides with the precession frequency. As the spin precession is
damped by spin-orbit interaction, the absorption spectrum shows a
broadened line, reflecting the lifetime of the spin precession. This
relaxation mechanism requires that the electrons be mobile. In metals,
this broadening frequently prevents observation of the electron spin
resonance (ESR). In the paper, the ESR is analyzed and it is shown
that spin relaxation of heavy fermions due to spin-orbit interaction
is much reduced, since only the “light” conduction electrons are
affected, contributing only a small fraction to the spin relaxation of
the heavy quasiparticles. In addition, a ferromagnetic tendency leads
to further narrowing of the ESR line. Heavy fermions may thus be
imaged by magnetic resonance. Indeed this resonance has been seen
recently in several compounds.
***
LP10932
Basic Advances in Nucleation Theory
Several conceptual problems in classical nucleation theory were found and addressed using example of sublimation (i.e. phase transformation from solid to gas) inside solid under applied tensile pressure. Traditionally, for any phase transformation, appearance of a critical nucleus is studied, which has equal probability to grow or disappear. Nuclei of a smaller size (subcritical nuclei) mostly disappear and since behavior of a system is reversible, no changes in material are observed after their disappearance. In contrast, when gas appears inside solid, it creates high pressure which expands a hole in solid significantly and plastically, i.e. irreversibly. This irreversibility creates numerous conceptual problems, which were not known in classical nucleation theory. In particular, we found that some subcritical nuclei do not disappear, but remain as stable nanovoids. Subcritical nuclei cannot grow via solid-gas transformation; however some of them expand mechanically like balloon, transforming themselves into supercritical nuclei, which can grow. Also, due to plastic irreversibility, classical definitions of the thermodynamic driving force and activation energy fail and have been generalized in the paper. New theory are important for the processes occurring during shock loading and laser treatment of materials.
***
LS11717
Arithmetic division: not so simple!
Learnt in elementary school, division is one of the four basic
arithmetic operations. Yet division gives rise to complicate results
such as the prime number phenomenon that for centuries has amazed
mathematicians and physicists. Going beyond, a group of collaborators
from Spain and Mexico have unveiled the complex dynamics that
underlays a process of repeated divisions. By introducing a very
simple model they call "the division game", they show that random
divisions on integers display the same avalanche-phenomena of critical
self-organization found on physical situations such as plate
tectonics, sand piles, stock market crashes and others. Moreover, the
authors show that integers can be thought as if organized in a complex
network with scale-free topology, a property shared by social networks
or gene regulatory networks, and that this topology -precisely- is the
mechanism inducing self-organized criticality. This may help to
explain the ubiquity of this phenomenon in nature.
***
LS11407
Shoving nanoparticles
The dynamics of frictional motion are critical to fields ranging from
nanomachines to the study of earthquakes. Despite the immense practical and
fundamental importance of friction, much of the basic physics of the problem
is not well understood and a detailed fundamental theory describing the
dynamics of frictional motion is far from complete. In a recent paper by
Dietzel et al. [1] intriguing new physics was revealed based on a novel
approach for nanoscale friction studies by pushing nanoparticles with the
tip of an atomic force microscope.
The results of the experiments indicated that two very different modes of
frictional behavior can coexist. The first mode shows a roughly linear
increase of the frictional force with contact area of an island, which
agrees with the classic explanation of the Amontons-Coulomb friction law.
The second mode of friction, which is observed for a smaller fraction of the
particles in these experiments, is entirely different. These particles
exhibit superlubricity, i.e. nearly zero frictional resistance.
What is going on here? According to recent simulations [2] the default state
of an interface composed of two flat surfaces, whose atoms are arranged in
an incommensurate fashion, would be frictionless behavior. However, a very
small number of "dirt" particles that get trapped between the two surfaces,
can lead to a dynamic interlocking of the surfaces yielding the classic
Amontons-Coulomb friction law. The authors speculate that mobile surface
molecules, which act as atomic friction mediators, may be present even under
the extremely clean ultrahigh vacuum conditions used in their experiments.
***
LS11622
Efficient and broadband coupling of quantum dots to a photonic crystal
waveguide - an all-solid-state on-chip single-photon source.
An efficient single-photon source is the key component in quantum
information applications such as quantum cryptography, and can be
utilized as the quantum resource for quantum computing. Semiconductor
quantum dots are high quality single-photon emitters; however it appears
a challenge to collect the emitted photon with high efficiency. One
successful approach has been to couple the quantum dot to the mode of a
nanocavity, however this technique works only in a narrow bandwidth, and
the out coupling of the photon is troublesome. Recently a way of
overcoming these limitations was proposed using a photonic crystal
waveguide. In a photonic crystal waveguide, light propagation can be
slowed down significantly, which enhances the coupling of the emitted
photon into the optical mode of the waveguide. In a recent article in
Physical Review Letters [101, 113903, 2008] Toke Lund-Hansen and
co-workers demonstrate that a photon emitted from a quantum dot is
efficiently transferred to a photonic crystal waveguide. It is observed
that the coupling efficiency is as high as 89 % extending over an
unprecedented bandwidth of 20 nm, consequently outperforming photonic
crystal nanocavites. The technology is promising for on-chip single
photon generation with applications for all-solid-state quantum
information processing.
***
BS10812
Semiconductor Band Gaps Simply Calculated
The density-functional calculation of semiconductor energy band gaps
is revisited. Semiconductor band gaps are technologically so important
that improving the quality of the calculated result is a
necessity. Our technique is inspired in the Slater's "transition state"
for which we found a definition in a many-atom system.
We show that the transition state is equivalent to the
inclusion of an electron self-energy. The self-energy is then
calculated using the atomic self-energy potential. The technique
uses just one non ab initio parameter, but which is determined by a
variational
principle. Aside from the precise calculated band gaps of many
semiconductors, the inclusion of the self-energy into the theory
leads to the conclusion that the electronic excitations of
a many-atom system (electrons and holes) are localized and not
diffuse as a Bloch wavefunction.
***
BR10983
Hypothetical three-dimensional all-sp^2 carbon phase
It is usually believed that the shorter the bond between two atoms,
the stronger. In pure carbon crystals, the bond length strongly
depends on the number of bonds that one carbon atom forms: from 1.42 Å
in graphite (three bonds) to 1.54 Å in diamond (four bonds). However,
despite its shorter bond length graphite is known as an excellent
lubricant, and diamond, in contrast, is known as the hardest material.
The problem is that graphite is intrinsically soft because of its two-
dimensional nature. Hence, in the quest of new hard or low
compressibility materials, several hypothetical three-dimensional (3D)
networks of threefold-bonded carbon atoms have been proposed in the
literature, all of them revealing a certain hardness but smaller than
diamond. Recently, a new hypothetical crystal, called K4, has been
proposed [1] with the same mathematical symmetry as diamond but with
threefold-bonded carbon atoms. Using first-principles calculations, we
have investigated the K4 crystal and compared it to previously
proposed models. We have analyzed why the hardness of these networks
is smaller than that of diamond, finally questioning the possibility
to create carbon materials harder than diamond using a 3D structure
with threefold-bonded atoms.
***
ETR1029
Elasticity-mediated nematiclike bacterial organization in model
extracellular DNA matrix
DNA is a common extracellular matrix component of bacterial biofilms in
cystic fibrosis airways. We find that bacteria can spontaneously order
in a matrix of aligned concentrated DNA, in which rod-shaped cells of
Pseudomonas aeruginosa follow the average orientation of the extended
DNA
chains. We demonstrate that this unidirectional alignment of bacteria
is ensured by elasticity and liquid crystalline properties of the DNA
matrix. These findings elucidate a new aspect of how the organizational
behavior of planktonic bacteria may be modified in extracellular
polymeric
substances of bacterial biofilms, as well as illustrate the potential
of using complex fluids to manipulate embedded nano- and micro-sized
active particles.
***
EF10476
Atomic force microscopy analysis of cell volume regulation
The regulation of cell volume in animal cells is usually modelled with
the cell treated as a membrane vesicle with folds. The interior is
assumed to be filled with saline and passive macromolecule solutes.
Laplaces law, which is a force balance equation independent of
constitutive properties, predicts that hypoosmotic solutions should
cause cells to swell, and since membranes are relatively inextensible,
cause the cell surface to stiffen. We tested this with the AFM using a
high precision algorithm that permitted long term, drift free,
recordings. Counter intuitively, swelling reduced the stiffness or
left it unchanged. The cells that became softer also became
mechanically hyperactive, and this hyperactivity persisted even after
the cells homeostatic volume decrease reached steady state. In
contrast to an osmotic challenge (250mOsm 6Atm), direct hydrostatic
pressure applied to the cell interior through a patch pipette required
only 0.03Atm to cause pronounced stiffening. Thus, intact cells
respond to an osmotic challenge more like sponges than vesicles.
Sponges are made of macromolecules whose osmotic pressure decreases
with the extent of crosslinking. When a sponge swells, the work, PV
required to stretch the latticework increases the effective activity
of the water in the sponge and accounts for the sponges limited
swelling in bulk water. Since the cells cytoskeleton is capable of
active contraction and relaxation, cells may be able to pump water
directly without necessarily coupling the water flux to membrane
limited solute transport.
***
CTR1014
Superfast quarks at the core of protons and neutrons.
Scientists scatter electrons from matter to probe the quark sub-structure of
neutrons. Low energy scattering tells us about where the up and down quarks
live within the neutron, while high energy measurements tell us how fast they
move. This work demonstrates how the fastest quarks provide the core of the
neutron, linking the information obtained in these different regions.
Last year, Gerald A. Miller, a UW physics professor, provided a new way to
extract a two-dimensional "snapshot" of the quarks in a fast moving neutron.
This confirmed the common view that there was a negative cloud of charge
outside of a positive region, but also showed an unexpected feature: a small
core of negative charge. A new work by Miller and ANL physicist John
Arrington explains this result through it's connection to information on high
speed quarks obtained in high energy measurements.
A single high speed quark can carry the bulk of the neutron's energy,
providing the seed around which other quarks cluster in forming the neutron.
High energy scattering has shown that in the neutron, these seeds are almost
entirely negatively-charged d-quarks, leading to a small central core of
negative charge. This explains the previously unexpected result while also
providing a new connection between high and low energy data that have
historically been examined independently from one another.
***
LU11926
Using Synchronization to Forecast Chaotic Behavior
The ability to predict the future based on past observations is
important in weather prediction, telecommunications, economic
forecasting and biomedical engineering. We describe a new method that
uses the phenomenon of synchronization of a computational model in
order to assimilate data output from an experimental system obtained
from measurements of an accessible variable. For systems where the
dynamics can vary in complexity from simple and periodic to chaotic
and highly irregular, it is difficult to measure all the relevant
variables needed to completely specify the state of the system. A
further complication occurs when the state depends on the history of
system evolution over a past time interval. Our method can both
assess the accuracy of a computational model and also predict the
future of the system for a limited time. We demonstrate this approach
quantitatively for an optoelectronic feedback loop that has been used
to generate waveforms for high-speed fiber-optic chaotic
communications and is a possible candidate for message encryption.
***
LB10976B
X-ray diffraction measurement errors
The failure of measuring volume expansion with x-ray diffraction
Perhaps the most important experimental technique to look at the atomic
world is x-ray diffraction. It has been a foundation for modern condensed
matter physics for about a hundred years. It is an accepted method to
determine the distance between atomic planes and thus thickness of films if
the number of atomic planes is known. In this paper, we show that x-ray
diffraction yields a radically different result to measuring changes of
thickness directly using a method called x-ray reflectivity. Changes in
thickness arise from reversible elastic swelling of a metallic superlattice
by controlled loading with hydrogen. As the superlattice expands the total
thickness changes, x-ray diffraction gives the wrong value. The deviation
between the methods depends on the amount of hydrogen inside the
superlattice in a complex way. The results highlight the general idea that
materials that undergo anisotropic deformation or changes in defect density
can not have their volume expansion characterised simply by determination of
mean interatomic distances.
***
BU10815
The peculiar magnetism of cobaltates
In this article, we establish the systematic presence of magnetic correlations
in sodium cobaltates, a family of materials with exotic electronic properties
including superconductivity. Compared to the already known behavior
("ferromagnetic correlations", see Figure) at high sodium content, a
different behavior ("antiferromagnetic correlations") is demonstrated for low
sodium content. It was until now a widely-held view that no magnetism was
present in the latter case. In light of the expected electronic structure,
this constituted a paradox, which is now weakened if not irrelevant. The
existence of these two magnetic behaviors appears to be a fundamental
characteristic of these compounds, which will guide future explanation of the
exotic properties. Besides, we show clear evidence of a key temperature T*,
dependent on the sodium content (i.e. the electronic doping), for which the
electronic response of the system to excitation (its electronic
susceptibility) is maximum. This constitutes a so-called energy scale, which
hints at previously-unknown physics, possibly linked to the change in
magnetic behavior mentioned here above. A striking parallel can be drawn with
other low-dimensional (2D, 1D) materials exhibiting strong electronic
interactions and related properties.
***
LR11410B
Super-sharp image out of a cylindrical superlens
Now you can obtain super-sharp images out of a cylindrical superlens! A
superlens is a lens providing subwavelength imaging, while a conventional
lens can only have a resolution on the order of one wavelength due to the
diffraction limit. Superlens in a slab shape was theoretically proposed a
number of years ago. However, a slab superlens is infinitely extended. Hence
it has to be truncated in practical realizations, which not only leads to
degradation of image quality but also prevents device miniaturization. In
this paper, we propose a type of cylinder-shaped superlens, which is
confirmed to be an almost exact parallel to the slab superlens in imaging
performance but with a finite cross-section. Our analytical calculations
show that such a cylindrical lens, even with a cross-section size comparable
to wavelength, can achieve similar sub-wavelength imaging resolution as
compared to the previously reported slab lens. We envisage that such a
cylindrical superlens can be fabricated using the metamaterial technology,
and can be handled with great flexibility for performing various imaging and
lithography tasks. Our idea can also be easily extended to design spherical
superlenses or other types of practical three-dimensional superlenses.
***
ZV10030
High-resolution camera system revealed undiscovered defects on the
inner surfaces of cavities.
High-resolution camera system newly developed for inspection of superconducting RF cavity inner surface revealed undiscovered defects
on the inner sides of the cavities predicted by other measurements.
Almost all of the defects are found at vicinities of the electron
beam welding seams. This system is developed in order to study the
relation between the achievable accelerating field gradient and the
defects in the inner surface. The inspection system consists of a
high resolution CMOS camera and a special illumination system built
in a cylinder that has a diameter of 50 mm. The camera cylinder can
be inserted into the L-band 9 cell-superconducting cavity. The system
provides a resolution of about 7.5 µm/pixel. Thus far, there have
been good correlations between locations identified by thermometry
measurements and positions of defects found by this system. The
heights or depths of the defects can also be estimated by measuring
wall gradients using the reflection angle relation between the camera
position and the strip illumination position.
This system should be a useful tool for improving not only production
yield of such cavities but also general electron beam welding qualities.
***
AS10345B
Giant Terahertz Surface Plasmons on a Wire
We propose a method to make high intensity terahertz surface plasmons by
shooting electron bunches onto the tip of a pointed wire. By solving
Maxwell's equations for a metal cone, we show that the plasmons created
this way will be orders of magnitude stronger than any wire-bound
terahertz plasmon made so far.
Terahertz radiation has wavelengths in between that of visible light and
microwaves. It is ideal for studying, e.g., charge carrier dynamics and
biomolecules. Moreover, it enables early skin cancer diagnosis and forms
a harmless alternative to security X-rays ('T-rays'). The potential of
terahertz radiation is enhanced even further if the radiation can be
compressed into a volume much smaller than the wavelength. This greatly
boosts the radiation intensity while attaining a micrometer resolution.
Sub-wavelength compression can be achieved if the radiation is confined
to a surface, in the form of so-called 'surface plasmons'. However, an
efficient technique for generating terahertz surface plasmons is still
lacking.
Our method provides such a technique. Our calculations show that
terahertz plasmons of MV/cm field strength can be created on a 1 mm
thick metal wire, using established electron bunch technology.
Sub-wavelength compression of these wire-bound plasmons, for example by
simply tapering the wire back into a tip, will lead to terahertz fields
of unprecedented strengths.
***
AT10349
Mid-infrared room temperature semiconductor laser
A semiconductor laser for the generation of mid-infrared electromagnetic radiation at room temperature is suggested.
Due to possibility to work without any cryogenic cooling such a laser is expected to be a compact and
easy to operate device. This circumstance may make it useful not only for applications
in technology, but also in medicine. In this field portable and inexpensive
sources of infrared radiation (like the proposed device) are in great demand nowadays because of their necessity for
diagnostics and therapy. To achieve the room temperature operation
of this laser in this paper it is suggested to use some features of the structure of electron quantum energy levels
appearing in a very thin (the width of order a ten millionth of a centimeter)
semiconductor film (quantum well) placed between two other semiconductors.
For the generated mid-infrared radiation I also propose to employ a waveguide of a special design
allowing to minimize its losses. Adjusting semiconductor structure parameters, the suggested mid-infrared laser can be suited for
generation at any required wavelength in rather a broad mid-infrared wavelength range,
which allows one to use it in numerous applications.
***
AM10257
Einstein's special relativity simulated using optical polarizers
The everyday life laws of physics have to be modified for objects with velocities approaching the
speed of light. For these objects - for example, elementary particles in an accelerator - the
Einstein's special relativity supersede the usual Newtonian mechanics. As their velocities increase,
these objects experience a shortening of the distances and a slowing of time. Consequently, the usual
Galilean addition law of velocities has to be replaced by a more complicated relativistic composition law of velocities.
In this paper, we show that the polarization of a light wave obeys the same relativistic composition law
as velocities in special relativity. Hence, the laws of special relativity can be in principle simulated
with optical devices such as polarizers, retarders, and devices with optical activity. More precisely,
the light wave polarization can be described in a four dimensional space - as in special relativity -
where the time dimension is replaced by the energy of the light wave. In this space, the light wave
polarization follow a trajectory which depend on the optical device went through. Also, we demonstrate that
the polarization of a light wave going through a polarizer does not always follow the shortest trajectory between
the initial and the final polarization state as it was usually thought.
***
BU10875BR
Efficient magnetic memory recording with "spin current" pulses
While tiny "nano"-sized magnets are already used to read the information
stored on disk drives, future memory devices may use a fundamental magnetic
property of electrons, called spin, to write and store information on such a
nanomagnet itself. While previous research has shown that a stream of
magnetized electrons, a "spin current", can store information on a
nanomagnet, we demonstrate that several, extremely short "spin current"
pulses, if applied at precise times, can store this information with less
energy than a single, longer duration pulse. Furthermore, we show that by
adjusting the pulse amplitudes it is also possible to excite a nanomagnet
into controlled, large angle orbits to create a tunable microwave source.
This coherent control capability has the potential to significantly impact
development of energy efficient magnetic memory devices.
