22,097 research outputs found
Superconductivity in iron silicide Lu2Fe3Si5 probed by radiation-induced disordering
Resistivity r(T), Hall coefficient RH(T), superconducting temperature Tc, and
the slope of the upper critical field -dHc2/dT were studied in poly- and
single-crystalline samples of the Fe-based superconductor Lu2Fe3Si5 irradiated
by fast neutrons. Atomic disordering induced by the neutron irradiation leads
to a fast suppression of Tc similarly to the case of doping of Lu2Fe3Si5 with
magnetic (Dy) and non-magnetic (Sc, Y) impurities. The same effect was observed
in a novel FeAs-based superconductor La(O-F)FeAs after irradiation. Such
behavior is accounted for by strong pair breaking that is traceable to
scattering at non-magnetic impurities or radiation defects in unconventional
superconductors. In such superconductors the sign of the order parameter
changes between the different Fermi sheets (s+- model). Some relations that are
specified for the properties of the normal and superconducting states in
high-temperature superconductors are also observed in Lu2Fe3Si5. The first is
the relationship -dHc2/dT ~ Tc, instead of the one expected for dirty
superconductors -dHc2/dT ~ r0. The second is a correlation between the
low-temperature linear coefficient a in the resistivity r = r0 + a1T, which
appears presumably due to the scattering at magnetic fluctuations, and Tc; this
correlation being an evidence of a tight relation between the superconductivity
and magnetism. The data point to an unconventional (non-fononic) mechanism of
superconductivity in Lu2Fe3Si5, and, probably, in some other Fe-based
compounds, which can be fruitfully studied via the radiation-induced
disordering.Comment: 7 pages, 8 figure
Disorder-sensitive superconductivity in the iron silicide LuFeSi studied by the Lu-site substitutions
We studied effect of non-magnetic and magnetic impurities on
superconductivity in LuFeSi by small amount substitution of the Lu
site, which investigated structural, magnetic, and electrical properties of
non-magnetic (LuSc)FeSi,
(LuY)FeSi, and magnetic
(LuDy)FeSi. The rapid depression of by
non-magnetic impurities in accordance with the increase of residual resistivity
reveals the strong pair breaking dominated by disorder. We provide compelling
evidence for the sign reversal of the superconducting order parameter in
LuFeSi.Comment: 4 pages, 5 figure
Model Theory of Holomorphic Functions
This thesis is concerned with a conjecture of Zilber: that the complex field expanded with the exponential function should be `quasi-minimal'; that is, all its definable subsets should be countable or have countable complement. Our purpose is to study the geometry of this structure and other expansions by holomorphic functions of the complex field without having first to settle any number-theoretic problems, by treating all countable sets on an equal footing.
We present axioms, modelled on those for a Zariski geometry, defining a non-first-order class of ``quasi-Zariski'' structures endowed with a dimension theory and a topology in which all countable sets are of dimension zero. We derive a quantifier elimination theorem, implying that members of the class are quasi-minimal.
We look for analytic structures in this class. To an expansion of the complex field by entire holomorphic functions we associate a sheaf of analytic germs which is closed under application of the implicit function theorem. We prove that is also closed under partial differentiation and that it admits Weierstrass preparation. The sheaf defines a subclass of the analytic sets which we call -analytic. We develop analytic geometry for this class proving a Nullstellensatz and other classical properties. We isolate a condition on the asymptotes of the varieties of certain functions in . If this condition is satisfied then the -analytic sets induce a quasi-Zariski structure under countable union. In the motivating case of the complex exponential we prove a low-dimensional case of the condition, towards the original conjecture
Centrality and Energy Dependence of Proton, Light Fragment and Hyperon Production
Recent results of the NA49 collaboration are discussed. These include the
energy dependence of stopping and the production of the light fragments t and
3He. New data on the system size dependence of hyperon production at 40A and
158AGeV are also presented.Comment: 4 pages, Quark Matter 2006 proceeding
Two-gap superconductivity in single crystal LuFeSi from penetration depth measurements
Single crystal of LuFeSi was studied with the tunnel-diode
resonator technique in Meissner and mixed states. Temperature dependence of the
superfluid density provides strong evidence for the two-gap superconductivity
with almost equal contributions from each gap of magnitudes
and . In the vortex state, pinning
strength shows unusually strong temperature dependence and is non-monotonic
with the magnetic field (peak effect). The irreversibility line is sharply
defined and is quite distant from the , which hints on to enhanced
vortex fluctuations in this two-gap system. Altogether our findings provide
strong electromagnetic - measurements support to the two-gap superconductivity
in LuFeSi previously suggested from specific heat measurements
The electron spectra in the synchrotron nebula of the supernova remnant G 29.7-0.3
EXOSAT results obtained with the imaging instrument (CMA) and the medium energy proportional counters (ME) are discussed. Assuming that the featureless power-law spectrum obtained in the 2 to 10 keV range is synchrotron radiation from relativistic electrons, one derives constraints on magnetic field strength and age of the nebula. The energy spectra of the electrons responsible for the emission in the radio and X-ray ranges are discussed. The great similarity of the physical properties of G 29.7-0.3 and of three synchrotron nebulae containing a compact object observed to pulse in X-rays makes G 29.7 - 0.3 a very promising candidate for further search for pulsed emission. Further observations at infrared wavelengths might reveal the break(s) in the emitted spectrum expected from the radio and X-ray power-law indices and give us more information on the production of the electron populations responsible for the emission of the nebula
Enhanced quasiparticle heat conduction of the multigap superconductor Lu2Fe3Si5
The thermal transport measurements have been made on the Fe-based
superconductor Lu2Fe3Si5 (Tc ~ 6 K) down to a very low temperature Tc/120. The
field and temperature dependences of the thermal conductivity confirm the
multigap superconductivity with fully opened gaps on the whole Fermi surfaces.
In comparison to MgB2 as a typical example of the multigap superconductor in a
p-electron system, Lu2Fe3Si5 reveals a remarkably enhanced quasiparticle heat
conduction in the mixed state. The results can be interpreted as a consequence
of the electronic correlations derived from Fe 3d-electrons.Comment: 5 pages, 4 figure
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