76 research outputs found
Approaching Petavolts per meter plasmonics using structured semiconductors
A new class of strongly excited plasmonic modes that open access to
unprecedented Petavolts per meter electromagnetic fields promise wide-ranging,
transformative impact. These modes are constituted by large amplitude
oscillations of the ultradense, delocalized free electron Fermi gas which is
inherent in conductive media. Here structured semiconductors with appropriate
concentration of n-type dopant are introduced to tune the properties of the
Fermi gas for matched excitation of an electrostatic, surface "crunch-in"
plasmon using readily available electron beams of ten micron overall dimensions
and hundreds of picoCoulomb charge launched inside a tube. Strong excitation
made possible by matching results in relativistic oscillations of the Fermi
electron gas and uncovers unique phenomena. Relativistically induced ballistic
electron transport comes about due to relativistic multifold increase in the
mean free path. Acquired ballistic transport also leads to unconventional heat
deposition beyond the Ohm's law. This explains the absence of observed damage
or solid-plasma formation in experiments on interaction of conductive samples
with electron bunches shorter than . Furthermore,
relativistic momentum leads to copious tunneling of electron gas allowing it to
traverse the surface and crunch inside the tube. Relativistic effects along
with large, localized variation of Fermi gas density underlying these modes
necessitate the kinetic approach coupled with particle-in-cell simulations.
Experimental verification of acceleration and focusing of electron beams
modeled here using tens of Gigavolts per meter fields excited in semiconductors
with free electron density will pave the way for Petavolts
per meter plasmonics.Comment: 16 pages, 10 figure
From nonwetting to prewetting: the asymptotic behavior of 4He drops on alkali substrates
We investigate the spreading of 4He droplets on alkali surfaces at zero
temperature, within the frame of Finite Range Density Functional theory. The
equilibrium configurations of several 4He_N clusters and their asymptotic trend
with increasing particle number N, which can be traced to the wetting behavior
of the quantum fluid, are examined for nanoscopic droplets. We discuss the size
effects, inferring that the asymptotic properties of large droplets correspond
to those of the prewetting film
Energy landscape - a key concept for the dynamics of glasses and liquids
There is a growing belief that the mode coupling theory is the proper
microscopic theory for the dynamics of the undercooled liquid above a critical
temperature T_c. In addition, there is some evidence that the system leaves the
saddlepoints of the energy landscape to settle in the valleys at this critical
temperature. Finally, there is a microscopic theory for the entropy at the
calorimetric glass transition T_g by Mezard and Parisi, which allows to
calculate the Kauzmann temperature from the atomic pair potentials.
The dynamics of the frozen glass phase is at present limited to
phenomenological models. In the spirit of the energy landscape concept, one
considers an ensemble of independent asymmetric double-well potentials with a
wide distribution of barrier heights and asymmetries (ADWP or Gilroy-Phillips
model). The model gives an excellent description of the relaxation of glasses
up to about T_g/4. Above this temperature, the interaction between different
relaxation centers begins to play a role. One can show that the interaction
reduces the number of relaxation centers needed to bring the shear modulus down
to zero by a factor of three.Comment: Contribution to the III Workshop on Nonequilibrium Phenomena in
Supercooled Fluids, Glasses and Amorphous Materials, 22-27 September 2002,
Pisa; 14 pages, 3 figures; Version 3 takes criticque at Pisa into account;
final version 4 will be published in J.Phys.: Condens.Matte
Liquid 4He: contributions to first principles theory of quantized vortices, thermohydrodynamic properties, and the lambda transition
Liquid 4He has been studied extensively for almost a century, but there are
still a number of outstanding weak or missing links in our comprehension of it.
This paper reviews some of the principal paths taken in previous research and
then proceeds to fill gaps and create an integrated picture with more complete
understanding through first principles treatment of a realistic model that
starts with a microscopic, atomistic description of the liquid. Newly derived
results for vortex cores and thermohydrodynamic properties for a two-fluid
model are used to show that interacting quantized vortices may produce a lambda
anomaly in specific heat near the superfluid transition where flow properties
change. The nature of the order in the superfluid state is explained.
Experimental support for new calculations is exhibited, and a unique specific
heat experiment is proposed to test predictions of the theory. Relevance of the
theory to modern research in cosmology, astrophysics, and Bose-Einstein
condensates is discussed.Comment: 155 pages, 28 figure
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