237 research outputs found
Nodes of the Gap Function and Anomalies in Thermodynamic Properties of Superfluid He
Departures of thermodynamic properties of three-dimensional superfluid He
from the predictions of BCS theory are analyzed. Attention is focused on
deviations of the ratios and
from their BCS values, where is the pairing gap at zero
temperature, is the critical temperature, and and are the
superfluid and normal specific heats. We attribute these deviations to the
momentum dependence of the gap function , which becomes well
pronounced when this function has a pair of nodes lying on either side of the
Fermi surface. We demonstrate that such a situation arises if the P-wave
pairing interaction , evaluated at the Fermi surface, has a sign
opposite to that anticipated in BCS theory. Taking account of the momentum
structure of the gap function, we derive a closed relation between the two
ratios that contains no adjustable parameters and agrees with the experimental
data. Some important features of the effective pairing interaction are inferred
from the analysis.Comment: 17 pages, 4 figure
Ecologische analyse van potentiële locaties voor mosselzaadinvang (MZI) in Nederlandse kustwateren
Het doel van de ecologische analyse is aan te geven of, en zo ja welke, ecologische functies aan de orde zijn bij toepassing van mosselzaadinvang (MZI) in de gegeven zoekgebieden en wat de mogelijke effecten zijn. De analyse is gebaseerd op de resultaten van eerdere MZI evaluaties en gericht op mogelijke effecten op draagkracht, bodem, vogels en zeezoogdieren. Omdat het gaat om een vergelijking van gebieden is de aandacht vooral gericht op effecten die ruimtelijk verschillend kunnen uitwerken. Op basis van deze studie kan een keuze worden gemaakt van een redelijk groot aantal locaties waarvoor geen omvangrijke nadelige effecten van MZI toepassingen worden verwacht. Deze locaties bevinden zich in de Waddenzee, Voordelta en Oosterschelde, met een evenredige verdeling over deze gebieden
Sputtering yields exceeding 1000 by 80keV Xe irradiation of Au nanorods
Using experiments and computer simulations, we find that 80 keV Xe ion irradiation of Au nanorods can produce sputtering yields exceeding 1000, which to our knowledge are the highest yields reported for sputtering by single ions in the nuclear collision regime. This value is enhanced by more than an order of magnitude compared to the same irradiation of flat Au surfaces. Using MD simulations, we show that the very high yield can be understood as a combination of enhanced yields due to low incoming angles at the sides of the nanowire, as well as the high surface-to-volume ratio causing enhanced explosive sputtering from heat spikes. We also find, both in experiments and simulations, that channeling has a strong effect on the sputtering yield: if the incoming beam happens to be aligned with a crystal axis of the nanorod, the yield can decrease to about 100
Coherent effects in double-barrier Josephson junctions
The general solution for ballistic electronic transport through
double-barrier Josephson junctions is derived. We show the existence of a
regime of phase-coherent transport in which the supercurrent is proportional to
the single barrier transparency and the way in which this coherence is
destroyed for increasing interlayer thickness. The quasiparticle dc current at
arbitrary voltage is determined.Comment: 4 pages, 2 figures, submitted to Phys. Rev.
Hole dynamics and photoemission in a t-J model for SrCu_2(BO_3)_2
The motion of a single hole in a t-J model for the two-dimensional spin-gap
compound SrCu_2(BO_3)_2 is investigated. The undoped Heisenberg model for this
system has an exact dimer eigenstate and shows a phase transition between a
dimerized and a Neel phase at a certain ratio of the magnetic couplings. We
calculate the photoemission spectrum in the disordered phase using a
generalized spin-polaron picture. By varying the inter-dimer hopping parameters
we find a cross-over between a narrow quasiparticle band regime known from
other strongly correlated systems and free-fermion behavior. The hole motion in
the Neel-ordered phase is also briefly considered.Comment: 4 pages, 3 fig
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