LS11321
Agglomerates do it better
How do exotic particles in condensed-matter systems organize
in order to traverse nearly impenetrable barriers? Will they line
up quietly and cross one by one, or will they wait until a little
chattering crowd forms before embarking noisily on the perilous
quest? Previously unexplained experiments in the quantum Hall
regime [1] tell us that these particles may clump together when...
it is cold enough.
In this paper LS11321 we provide a microscopic explanation of this
peculiar behaviour. At the lowest attainable temperatures of a few
milliKelvins, we prove that it is fractional statistics that makes
it easier for agglomerates of quasiparticles to cross the tunnel
barrier. This tendency to bunch together can be
detected by "hearing" the racket of the tunneling agglomerates
through current noise measurements.
The scenario we depict accounts for a broader spectrum
of experimental data, shedding new light on fractional statistics
particles and their intricate collective habits.
***
BT11071
Finding Needles in a Haystack
We found unusually narrow, needle-like features in the bilayer manganite
phase diagram, as a function of strontium substitution for lanthanum, that
were completely missed previously. At the heart of our achievement was
synthesis of crystals with highly uniform strontium substitution and a
method to verify that uniformity. A small gradient of strontium
concentration, intrinsic to our growth technique, is used to map out the
qualitative shape of these needle-like charge-ordered phases and that shape
agreed with the predictions of our simple entropy argument. Prominent
correlated electron materials often result from a similar substitution
(dopant) in a parent compound. In many cases there is an intense
competition among the possible electronic or magnetic phases that depends
sensitively on the dopant concentration. The homogeneity we achieved and
verified is invaluable for any doped system to isolate phases from their
neighbors. It thus allowed us to rule out an erroneous conclusion of local
coexistence of antiferromagnetic phases with the charge-ordered phases that
had been ubiquitously reported in numerous previous studies.
***
BR 10675
Klein tunnelling and photon assisted transport in Graphene
Charge carriers in a single layer of graphite, graphene, exhibit unique
properties. They can travel unimpeded through high and wide potential
barriers- Klein tunneling. In this work, we show that Klein tunneling
occurs even for oscillating barriers. Charge carriers traversing the
oscillating potential barrier exchange energy in discrete quanta
resulting in photon assisted transport in graphene.
***
LU12059
Correlated electron tunneling through two separate quantum dot systems with strong capacitive interdot coupling
Using a pseudo-spin description is a very common concept in physics
which shows that - at first look - different systems obey the
same physics. It is known that the degree of freedom in occupying
a localized state by an electron of either spin up or down from an
electron reservoir containing both spin orientations lead to the
formation of a highly correlated many-electron state.
Despite the simplicity of the arrangement the resulting state is highly
non-trivial and one of the most fundamental effects in theoretical solid
state physics, coined after the Japanese physicist Jun Kondo.
The Kondo effect has been measured in electrical transport through
single quantum dot systems where it can overcome the Coulomb blockade
of the conductance at low temperatures. In our work we demonstrate that
two quantum dot systems which, individually and mutually, are in the
Coulomb blockade regime become both conducting even though the interaction
between them is purely electrostatic. This is because of the
aforementioned Kondo effect, albeit in terms of a pseudo-spin
associated with the two
quantum dot systems. A big advantage of our pseudo-spin realization is
the much better experimental control over the system.
***
EU10307
Slow changes in mixtures of glass
How does a glass made from two different components behave?
The physical properties of glasses change over long times.
This is known as aging. In this paper we show that it is the
particles which are most mobile when in a pure sample that set
the aging agenda for both species. We study a mixture composed
of tiny plastic particles of two sizes suspended in a liquid.
This model system acts like a glass when the particle concentration
is increased. Using an optical confocal microscope, we directly
view particle motions in 3D. We observe three key features of
aging in two-component mixtures: 1) particles move in cooperative
groups, just as had been observed in previous work; 2) These mobile
groups tend to be richer in small particles; and 3) these small
particles facilitate the motion of nearby particles of both sizes.
Our work is a step towards the microscopic understanding of real
world glasses which are often complex multi-component materials
and which remain a deep puzzle.
***
LR10980
To reduce drag, flag in front!
Racing cars and bicyclists can reduce air resistance by following closely
behind a leader, but we find that this conventional fluid drafting or
slip-streaming is reversed for undulating objects. Inspired by schooling
fish and flocking birds, we studied how flapping flags change the fluid
drag forces on one another when grouped together in a flowing fluid. To
our surprise, we discovered that the leading flag enjoys a drag reduction
(up to 50%) while its downstream neighbor suffers a significant drag
increase. If this effect applies to fish schools and bird flocks, the
leaders would also have a reduced burden and spend less energy as they
swim or fly.
***
LP11389
Cosmological magnetic fields from matter genesis
The genesis of matter is shown to be accompanied by the creation
of a cosmic magnetic field that can provide a window to the very
early universe. Particle physics models of cosmic matter-genesis
rely on transitions through exotic intermediate states which decay
and produce helical magnetic fields as a by-product. The strength,
coherence and helicity of the cosmic magnetic field today depends
on the physics of matter-genesis nano seconds after the big bang.
Detection of such cosmic magnetic fields would give
information about the origin of matter that is complementary to
that from particle accelerators, and may be within reach of planned
observations.
***
LS11507
Using sound reinforcement amplifiers to cool and trap atoms
for new types of collision studies.
In this work we use high power sound reinforcement amplifiers (the
same as are used at rock concerts) to cool and trap atoms to
temperatures only 250 millionths of a degree above absolute zero in a
novel type of atom trap - the AC-MOT. By driving the magnetic and
laser fields required to trap the atoms at audio frequencies, we can
switch the trap on and off in only a few millionths of a second -
allowing us to efficiently fire charged particles into these cold
targets and study the subsequent excitation and ionization that
occurs. This new technique opens up cold atom research to the field
of collision physics, and this allows us to produce new and precise
data about these interactions. We have demonstrated this technique
using electron ionization of cold potassium atoms, and expect this
new method to be widely adopted by cold atom and collision physicists
in the near future.
***
LT11400
Strong Excitonic Effect in Cuprates
Another important ingredient to explain the physics of cuprates is suggested. The high temperature superconductivity (HTSC) in cuprates is obtained by carrier doping in its insulating parent materials. These undoped materials, so called Mott insulators, become insulating due to a strong Coulomb interaction between carriers. It is important to understand the parent compound to understand the HTSC. In this paper, temperature dependent optical spectra of a one dimensional chain compound Sr2CuO3 were presented. For one dimensional systems, interactions not only between carriers at a same site but also between carriers at neighboring sites have been considered. Interestingly, the obtained spectrum at low temperature showed narrow bound exciton peaks which can exist only with a sizable inter-site interaction. The inter-site interaction has seldom been considered in the physics of two dimensional cuprates because a weak inter-site interaction is believed to play a minor role to renormalize the intra-site interaction strength. However, this study suggests that the inter-site interaction is strong enough even to form bound excitons. Moreover, it demands the long range Coulomb interaction to be considered. This result should encourage theorists to take the inter-site interaction into account to explain the physics of cuprates and its HTSC.
***
LU11781
Tracks tracked: revealing the structure of an ion track in glass
Heavy ions at high velocities can leave permanent trails of damage
termed ion tracks as they traverse a solid - but the mechanisms
behind this have remained controversial for decades. Now an
Australian-European Research team has come a big step closer to
solving the mystery by measuring and simulating the structure of an
ion track in glass (amorphous SiO2). The finding is a milestone in
understanding the interaction of highly energetic ions with solids
and has ramifications for materials science, nuclear physics,
geochronology, archaeology and interplanetary science. Using advanced
synchrotron techniques, the researchers have now resolved subtle
changes in density at length scales of tens of atoms across an ion
track. Calculations and simulations using a local heat spike about
the ion trajectory demonstrate the track structure is consistent with
a frozen-in nano-scale acoustic shock wave. This shock wave is
generated by the sudden thermal expansion at the ion track center as
the ion passes through the solid yielding lattice temperatures
greater than that required for melting. Upon rapid quenching of this
molten track, the research team has experimentally and theoretically
established that ion tracks are actually comprised of a less-dense
core surrounded by a more-dense shell (relative to unirradiated material).
***
LT11544
NanoDominoes
A longitudinal domino wave can be developed in a single-walled carbon nanotube. Domino phenomenon, which originally refers to the successive toppling of a row of dominoes when the first one is knocked over, widely exists in natural systems (e.g., avalanche of snow). It has been shown that a molecular domino cascade may be used to perform mechanical calculation on the nanometer length scale (Heinrich et. al., Science 298, 1381, 2002). In this paper, we demonstrate that after a collapse of a nanotube cross section a longitudinal domino wave is produced. The wave is driven by van der Waals potential energy and its natural speed may be up to 1 km/s. Molecules inside a SWCNT can be accelerated by the domino wave and finally shot out, allowing a SWCNT to be an energy supplier. The finding provides opportunities for designing new concept (domino-driven) NEMS devices, such as a nano gun (with a muzzle velocity 10 times of a Desert Eagle pistol).
