430 research outputs found
Induced Kramer-Pesch-Effect in a Two Gap Superconductor: Application to MgB2
The size of the vortex core in a clean superconductor is strongly temperature
dependent and shrinks with decreasing temperature, decreasing to zero for T ->
0. We study this so-called Kramer-Pesch effect both for a single gap
superconductor and for the case of a two gap superconductor using parameters
appropriate for Magnesium Diboride. Usually, the Kramer-Pesch effect is absent
in the dirty limit. Here, we show that the Kramer-Pesch effect exists in both
bands of a two gap superconductor even if only one of the two bands is in the
clean limit and the other band in the dirty limit, a case appropriate for MgB2.
In this case an induced Kramer-Pesch effect appears in the dirty band. Besides
numerical results we also present an analytical model for the spatial variation
of the pairing potential in the vicinity of the vortex center that allows a
simple calculation of the vortex core radius even in the limit T -> 0.Comment: 12 pages, 12 figure
Proximity fingerprint of s+- superconductivity
We suggest a straightforward and unambiguous test to identify possible
opposite signs of superconducting order parameter in different bands proposed
for iron-based superconductors (s+- state). We consider proximity effect in a
weakly coupled sandwich composed of a s+- superconductor and thin layer of
s-wave superconductor. In such system the s-wave order parameter is coupled
differently with different s+- gaps and it typically aligns with one of these
gaps. This forces the other s+- gap to be anti-aligned with the s-wave gap. In
such situation the aligned band induces a peak in the s-wave density of states
(DoS), while the anti-aligned band induces a dip. Observation of such
contact-induced negative feature in the s-wave DoS would provide a definite
proof for s+- superconductivity.Comment: 4 pages, one figur
Dust emission of Comet Halley at large heliocentric distances
Comet Halley is currently approaching the inner solar system. Four spacecrafts (NASA's spacecraft, two Russian Vega probes and the Japanese MS-T5 spacecraft) have already been launched to encounter the comet in March 1986. Two additional Halley probes (the European Giotto spacecraft and another Japanese Planet-A probe) will be launched in mid-85 to join the armada. Observations of dust emissions from Halley's Comet are discussed. The evaporation of cometary ices causes the emission of particulates from the nucleus. These observations will be used to determine the fly-by strategy of the Giotto spacecraft by taking into account the distribution of dust in the vicinity of the nucleus and the associated hazard for the space mission
Novel surgical technique for complete traumatic rupture of the pancreas: A case report
<p>Abstract</p> <p>Introduction</p> <p>Complete pancreatic rupture is a rare injury. The typical mechanism by which this occurs is overstretching of the pancreas across the vertebral column during blunt abdominal trauma. The management of this injury depends on the location and extent of the injury.</p> <p>Case presentation</p> <p>A 45-year-old Caucasian woman presented with blunt abdominal trauma after she fell onto the end of a handlebar during a bicycle accident. She arrived in the emergency room with stable vital signs and an isolated bruise just above the umbilicus. A computed tomography scan revealed a complete rupture of the pancreas, just ventral to her superior mesenteric vein, and an accompanying hematoma but no additional injuries. An emergency laparotomy was performed; the head of the pancreas was oversewn with interrupted sutures and this was followed by a two-layer pancreaticojejunostomy with the tail of the pancreas. The recovery after surgery was completely uneventful.</p> <p>Conclusions</p> <p>Isolated complete pancreatic rupture is a rare injury that can be managed with complete organ preservation. The combination of suturing the pancreatic head and two-layer pancreaticojejunostomy with the pancreatic tail is a feasible technique to manage this condition.</p
Single vortex structure in two models of iron pnictide superconductivity
The structure of a single vortex in a FeAs superconductor is studied in the
framework of two formulations of superconductivity for the recently proposed
sign-reversed wave () scenario: {\it (i)} a continuum model taking
into account the existence of an electron and a hole band with a repulsive
local interaction between the two; {\it (ii)} a lattice tight-binding model
with two orbitals per unit cell and a next-nearest-neighbour attractive
interaction. In the first model, the local density of states (LDOS) at the
vortex centre, as a function of energy, exhibits a peak at the Fermi level,
while in the second model such LDOS peak is deviated from the Fermi level and
its energy depends on band filling. An impurity located outside the vortex core
has little effect on the LDOS peak, but an impurity close to the vortex core
can almost suppress it and modify its position.Comment: 17 pages, 15 figures. Accepted for publication in New Journal of
Physic
Determining gap nodal structures in Fe-based superconductors: angle-dependence of the low temperature specific heat in an applied magnetic field
Since the discovery of high-Tc LaO_1-xF_xFeAs, and other such systems based
on FeAs layers, several proposals have been made for the superconducting order
parameter Delta_k, on both phenomenological and microscopic grounds. Here we
discuss how the symmetry of Delta_k in the bulk can be determined, assuming
that single crystals will soon be available. We suggest that a measurement of
the dependence of the low temperature specific heat on the angle of a magnetic
field in the FeAs plane is the simplest such method, and calculate
representative specific heat vs. field angle oscillations for the various
candidate states, using a phenomenological band structure fitted to the DFT
Fermi surface.Comment: 5 pages, 4 figure
A Twisted Ladder: relating the Fe superconductors to the high cuprates
We construct a 2-leg ladder model of an Fe-pnictide superconductor and
discuss its properties and relationship with the familiar 2-leg cuprate model.
Our results suggest that the underlying pairing mechanism for the Fe-pnictide
superconductors is similar to that for the cuprates.Comment: 5 pages, 4 figure
Specifics of impurity effects in ferropnictide superconductors
Effects of impurities and disorder on quasiparticle spectrum in
superconducting iron pnictides are considered. Possibility for occurrence of
localized energy levels due to impurities within the superconducting gap and
the related modification of band structure and of superconducting order
parameter are discussed. The evolution of superconducting state with impurity
doping is traced.Comment: 9 pages, 8 figure
Point-Contact Spectroscopy in MgB_2: from Fundamental Physics to Thin-Film Characterization
In this paper we highlight the advantages of using point-contact spectroscopy
(PCS) in multigap superconductors like MgB_2, both as a fundamental research
tool and as a non-destructive diagnostic technique for the optimization of
thin-film characteristics. We first present some results of crucial fundamental
interest obtained by directional PCS in MgB_2 single crystals, for example the
temperature dependence of the gaps and of the critical fields and the effect of
a magnetic field on the gap amplitudes. Then, we show how PCS can provide
useful information about the surface properties of MgB_2 thin films (e.g. Tc,
gap amplitude(s), clean or dirty-limit conditions) in view of their
optimization for the fabrication of tunnel and Josephson junctions for
applications in superconducting electronics.Comment: 11 pages, 7 figures; Proceedings of 6th EUCAS Conference (14-18
September 2003, Sorrento - Italy
Superconductivity at the Border of Electron Localization and Itinerancy
The superconducting state of iron pnictides and chalcogenides exists at the
border of antiferromagnetic order. Consequently, these materials could provide
clues about the relationship between magnetism and unconventional
superconductivity. One explanation, motivated by the so-called bad-metal
behaviour of these materials, proposes that magnetism and superconductivity
develop out of quasi-localized magnetic moments which are generated by strong
electron-electron correlations. Another suggests that these phenomena are the
result of weakly interacting electron states that lie on nested Fermi surfaces.
Here we address the issue by comparing the newly discovered alkaline iron
selenide superconductors, which exhibit no Fermi-surface nesting, to their iron
pnictide counterparts. We show that the strong-coupling approach leads to
similar pairing amplitudes in these materials, despite their different Fermi
surfaces. We also find that the pairing amplitudes are largest at the boundary
between electronic localization and itinerancy, suggesting that new
superconductors might be found in materials with similar characteristics.Comment: Version of the published manuscript prior to final journal-editting.
Main text (23 pages, 4 figures) + Supplementary Information (14 pages, 7
figures, 3 tables). Calculation on the single-layer FeSe is added.
Enhancement of the pairing amplitude in the vicinity of the Mott transition
is highlighted. Published version is at
http://www.nature.com/ncomms/2013/131115/ncomms3783/full/ncomms3783.htm
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