How liquids hide the secret of glass cooperativity.
How can glassy cooperative dynamics take place without any apparent
or straightforward connection to structural changes?
To find an answer to one of the great unsolved problems of soft condensed
matter physics, the authors of this paper move along unexplored directions.
It was already known that the accessible potential energy surface
qualitatively changes in the supercooled liquids, due to the presence of
local minima, or inherent structures (IS). Here, with a novel perspective,
the authors are able to show for the first time that the IS
bear a signature of the cooperativity and heterogeneity displayed by
the dynamics: in the supercooled regime, their response to deformation
reveals the presence of large cooperative and heterogenous domains.
The approach proposed is similar to the one typically used for elastic solids but applied here in the fluid phase. In this way, they recognize
the static counterpart of the cooperative dynamics and support strong connections with recent studies on elastic properties of amorphous solids.
***
LU10980
An exotic state of matter could be observed using radio frequency (RF) fields
In our work, we propose how to observe an exotic state of matter,
related to superconductors, in a gas of ultracold atoms.
Superconductors are materials where electricity flows without losses.
Such materials are utilized for instance to create magnetic fields for
certain types of medical imaging and superfast trains. It would be of
great interest to find materials which are superconductors at ever
higher temperatures, to allow important applications such as lossless
transport of energy. For this goal, the physical mechanisms behind
high temperature superconductors and superfluids have to be understood
better. Ultracold atomic gases offer an ideal system to study such
mechanisms. There, it may be possible to realize exotic forms of
superfluidity: for instance the so called FFLO
(Fulde-Ferrel-Larkin-Ovchinnikov) state which is of interest not only
in context of superconductors but also, e.g., for pairing of
elementary particles such as quarks. In the FFLO state, the superfluid
and pairing characteristics vary spatially throughout the sample. In
our work, we have proposed a way to observe the FFLO state in
ultracold gases using RF-spectroscopy. The calculated response to the
radio frequency (RF) field shows clear signatures of the spatially
varying nature of this exotic state.
***
BT10758
Mechanical motion speeds up electric switching in nano-devices
Molecular or nano-electromechanical devices are characterized by a
coupling between the electronic and ionic (¿mechanical¿) degrees of
freedom. When they are traversed by an electrical current, these devices
can be pushed far from thermal equilibrium. Excitation of the mechanical
motion reduces the resistance of the device leading to a positive
feedback on the current itself. The electrical resistance can then be
found only self-consistently by the determination of the stationary
mechanical and electronic state of the device. A fully self-consistent
theory of this phenomenon for arbitrary electron-ion coupling strength
is presented in this paper.
For strong electron-ion coupling, the system can become multistable. At
low transport voltages, the current is suppressed due to a large
effective electron mass (polaronic effect), while at higher voltages the
excitation of the mechanical motion allows system to explore regions of
large currents not accessible at low voltages. The net effect is the
appearance of a rapid increase of the conductance as a function of
transport voltage in a narrow bias interval with a concomitant
acceleration of the switching time between the ¿off¿ to the ¿on¿ states
of the device. The complex behaviour is witnessed by the characteristic
forms of the mechanical and electric fluctuations. This model may help
to design nanoscale molecular and nanomechanical switches.
***
LG11596B
Quantum condensation in highly excited semiconductors
Quantum condensation phenomena like Bose-Einstein condensation (BEC) or
suprafluidity have been a highly fascinating topic in physics since decades.
While BEC has been experimentally verified in alkali gases, its observation
in semiconductors is still in demand.
In our paper, we present a theoretical approach to describe quantum
condensation in the electron-hole plasma (EHP) of excited semiconductors
using the framework of real-time Green's functions. Electrons and holes are
fermions forming bosonic bound states (excitons), similar to the formation of
molecules in atomic gases. Compared to the latter ones, however, the
description of the EHP is much more challenging since electrons and holes are
charged particles interacting via the Coulomb potential. We observe a
transition from a partially ionized EHP to a high density electron-hole
liquid connected with a change of the physical nature of the quantum
condensate (the so-called BEC-BCS crossover). In spite of this change, the
phase boundary of the quantum condensate (i.e., the critical temperature vs.
density) shows a smooth crossover from the Bose-Einstein condensate of
excitons to BCS states at high densities as expected for Fermi systems with
bound states.
***
BS11025
QUBIT DECOHERENCE BY ENTANGLEMENT WITH CLUSTERS
The quantum coherence of a spin or a quantum bit (qubit) may be lost due
to entanglement with environment such as nuclear spins of atoms in a
lattice hosting the qubit. It is nontrivial to solve the many-body
dynamics of a bath of interacting spins coupled to the qubit which induces
the entanglement. Wen and Liu discover that the qubit decoherence process
can be understood as gradual entanglement of the qubit with clusters of
bath spins of larger and larger size as time passes by. Coherent
oscillation instead of decoherence may also be observed for small spin
baths where a few finite-size clusters could dominate in the bath
dynamics. The cluster correlation theory forms a basis for decoherence
control. It may also be generalized to understand statistics of small
quantum systems at equilibrium with finite temperature.
***
LT11502
Sound Absorption in a Sandpile
Understanding the physical origin of the elastic wave absorption in earth
materials is of great importance in the fields of seismology, soil
mechanics and rock physics. Several mechanisms of intrinsic attenuation
were proposed in porous granular materials, including the Coulomb
frictional sliding between cracks and grain boundary contacts and the
viscous dissipation due to the bulk fluid flow in partially or fully
saturated rocks. In this work, we characterize the dissipations of
ultrasound in dry and weakly wet (¿humid¿) granular materials using the
multiple sound scattering. In a dry medium two distinct sources of
dissipation from the adsorbed solid films (impurity layers) are observed:
a frictional loss and a viscoelastic one. In a wet medium, we find that
the dissipation is dominated by a viscous loss due to the submicron-thick
liquid films trapped at the surface asperities. Adding more liquids
enables to form the hour-glass capillary menisci but doesn¿t increase the
energy loss. Our experiments are of considerable interest to understanding
the crucial role of grain surface properties in granular mechanics, such
as singing sands, and the effects of humidity-induced capillary
condensation in wet granular materials, including room-dry rocks.
***
LR11108
Learning Vortex Physics
Hurricanes and superconducting vortices have things in common: Both are
quite stable fluid like structures inducing catastrophic consequences when
displaced in space. In the first case the consequences are well known, in
the second one a “superconducting” wire cannot transport current without
dissipation, jeopardizing technical applications.
A large amount of actual applied research in superconductivity is devoted
to design traps to pin the core of the vortex into the material. Using
Nernst effect measurements we found a method to discover up to which
magnetic field dependent temperature the superconductor can transport
lossless electrical current. We found that by all indications in high
temperature superconductors there is a range of temperatures where vortex
elastic energy is quenched. Thus, in this region vortices are free to move
and the superconductor becomes useless to transport electrical current.
This seems not to be dramatic because this temperature region is
sufficiently high for most applications. However, the result suggests a
revision of what is accepted in vortex physics, in particular for some
oxide superconductors where the 2D vortices nucleated in layers are
assumed non-interacting with those of neighbor layers.
***
BS10890
The Best of Both Worlds
The quest for materials with ever higher superconducting
transition temperatures has been a long-standing focus of
condensed matter and materials physics. Superconductivity requires
two essential ingredients: the binding of electrons into pairs and
the establishment of long-range phase coherence of the pair
wave-function. Unfortunately, systems in which pairing is strong
typically do not exhibit a correspondingly high transition
temperature, T_c, due to their susceptibility to large phase
fluctuations. Conversely, large phase stiffness is a property of
all simple metals, but these typically have (at best) weak
pairing. An intriguing question then arises: Is it possible for a
composite system, made of a strong-pairing component and a
phase-stiff metal, to inherit the best of the two worlds leading
to a transition temperature higher than that of either of its
constituents? (Murphy's Law, of course, would imply that a
composite would combine the worst aspects of both ingredients.) We
have computed the superconducting transition temperature of a
simple model of a composite system consisting of a good metal with
no pairing, and a strongly paired system with no phase stiffness.
If the coupling between these two constituents is too weak, T_c is
reduced, as in the decoupled case, by strong phase fluctuations.
If the coupling is too strong, the pairing scale is exponentially
suppressed, again leading to a low T_c. However, for a well
defined range of intermediate couplings, we find a high T_c with a
magnitude set by the strong pairing scale of the decoupled system.
This finding complements the experimental observations of Millo et
al [1] and Bozovic et al [2] concerning the enhancement of T_c in
two-component epitaxial films of cuprate high temperature
superconductors, and suggests further avenues for finding higher
T_c's in artificial multi-component materials.
***
LN11417
Bursty-Feature of Plasma Turbulence Linked to Broadband Power Spectra
Low frequency turbulence is a major focus of plasma physics research
due to its role in transporting mass and energy across confining
magnetic fields. In this paper, we connect the measurement of an
exponential power spectrum to the presence of Lorentzian shaped pulses
in the corresponding time series data and argue that this is a
universal feature of plasma turbulence. In two different experiments,
fluctuations in plasma density and temperature produce power spectra
that exhibit an exponential frequency dependence. In one experiment
this spectral behavior coincides with the appearance of the Lorentzian
pulses as the plasma evolves away from classical transport to an
enhanced, or anomalous, transport regime. The attached figure shows a
spectrogram in which the exponential spectrum begins at approximately
5.5 ms, the same moment at which large pulses are observed in the
fluctuation measurement shown as the white trace in the contour area.
Both the pulses and the exponential power spectrum appear only during
the anomalous transport phase. The generation of the pulses is linked
to nonlinear interactions of drift-Alfven waves, which highlights the
importance of electromagnetic effects in plasma turbulence.
