9,511 research outputs found
Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:O
We report an unusual persistence of superconductivity against high magnetic
fields in the iron chalcogenide film FeTe:O below ~ 2.5 K. Instead of
saturating like a mean-field behavior with a single order parameter, the
measured low-temperature upper critical field increases progressively,
suggesting a large supply of superconducting states accessible via magnetic
field or low-energy thermal fluctuations. We demonstrate that superconducting
states of finite momenta can be realized within the conventional theory,
despite its questionable applicability. Our findings reveal a fundamental
characteristic of superconductivity and electronic structure in the
strongly-correlated iron-based superconductors.Comment: 10 pages, 3 figure
Evolution of Nanoporosity in Dealloying
Dealloying is a common corrosion process during which an alloy is "parted" by
the selective dissolution of the electrochemically more active elements. This
process results in the formation of a nanoporous sponge composed almost
entirely of the more noble alloy constituents . Even though this morphology
evolution problem has attracted considerable attention, the physics responsible
for porosity evolution have remained a mystery . Here we show by experiment,
lattice computer simulation, and a continuum model, that nanoporosity is due to
an intrinsic dynamical pattern formation process - pores form because the more
noble atoms are chemically driven to aggregate into two-dimensional clusters
via a spinodal decomposition process at the solid-electrolyte interface. At the
same time, the surface area continuously increases due to etching. Together,
these processes evolve a characteristic length scale predicted by our continuum
model. The applications potential of nanoporous metals is enormous. For
instance, the high surface area of nanoporous gold made by dealloying Ag-Au can
be chemically tailored, making it suitable for sensor applications,
particularly in biomaterials contexts.Comment: 13 pages, PDF, incl. 4 figures. avi movies of simulations available
at http://www.deas.harvard.edu/matsci/downdata/downdata.htm
Multi-site, multi-year monitoring of the oscillating Algol-type eclipsing binary CT Her
We present the results of a multi-site photometric campaign carried out in
2004-2008 for the Algol-type eclipsing binary system CT Her, the primary
component of which shows Delta Scuti-type oscillations. Our data consist of
differential light curves collected in the filters B and V which have been
analysed using the method of Wilson-Devinney (PHOEBE). After identification of
an adequate binary model and removal of the best-matching light curve solution,
we performed a Fourier analysis of the residual B and V light curves to
investigate the pulsational behaviour. We confirm the presence of rapid
pulsations with a main period of 27.2 min. Up to eight significant frequencies
with semi-amplitudes in the range 3 to 1 mmag were detected, all of which
surprisingly lie in the frequency range 43.5-53.5 c\d. This result is
independent from the choice of the primary's effective temperature (8200 or
8700 K) since the light curve models for the binary are very similar in both
cases. This is yet another case of a complex frequency spectrum observed for an
accreting Delta Scuti-type star (after Y Cam). In addition, we demonstrate that
the amplitudes of several of these pulsation frequencies show evidence of
variability on time scales as short as 1-2 years, perhaps even less. Moreover,
our analysis takes into account some recently acquired spectra, from which we
obtained the corresponding radial velocities for the years 2007-2009.
Investigation of the O-C diagram shows that further monitoring of the epochs of
eclipse minima of CT Her will cast a new light on the evolution of its orbital
period.Comment: 13 pages, 13 encapsulated Postscript figures. Tables~3, 4, 9 and 12
will be available in electronic form only. Astronomy and Astrophysics, in
process (2011). Replaced the abstract with its final versio
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