5,405 research outputs found
Low-lying excitations around a single vortex in a d-wave superconductor
A full quantum-mechanical treatment of the Bogoliubov-de Gennes equation for
a single vortex in a d-wave superconductor is presented. First, we find
low-energy states extended in four diagonal directions, which have no
counterpart in a vortex of s-wave superconductors. The four-fold symmetry is
due to 'quantum effect', which is enhanced when is small. Second,
for , a peak with a large energy gap is
found in the density of states, which is due to the formation of the lowest
bound states.Comment: 7pages, Revte
Pair-breaking in iron-pnictides
The puzzling features of the slopes of the upper critical field at the
critical temperature , , and of the
specific heat jump of iron-pnictides are interpreted as
caused by a strong pair-breaking
Half quantum vortex in superfluid He-A phase in parallel plate geometry
The half quantum vortex(HQV) in condensate has been studied, since it was
predicted by Salomaa and Volovik in superfluid He-A phase. However, an
experimental evidence for its existence has not been reported so far. Motivated
by a recent experimental report by Yamashita et al\cite{yamashita}, we study
the HQVs in superfluid He confined between two parallel plates with a gap D
10 m in the presence of a magnetic field H 26 mT
perpendicular to the parallel plates. We find that the bound HQVs are more
stable than the singular vortices and free pairs of HQVs, when the rotation
perpendicular to the parallel plates is below the critical speed, 2 rad/s. The bound pair of HQVs accompanies the tilting of -vector out of the plane, which leads to an additional absorption in NMR
spectra. Our study appears to describe the temperature and rotation dependence
of the observed satellite NMR signal, which supports the existence of the HQVs
in He.Comment: 5 pages, 5 figure
Possible f-wave superconductivity in SrRuO?
Until recently it has been believed that the superconductivity in
SrRuO is described by p-wave pairing. However, both the recent specific
heat and the magnetic penetration depth measurements on the purest single
crystals of SrRuO appear to be explained more consistently in terms of
f-wave superconductivity. In order to further this hypothesis, we study
theoretically the thermodynamics and thermal conductivity of f-wave
superconductors in a planar magnetic field. We find the simple expressions for
these quantities when and , which should be
readily accessible experimentally.Comment: 6 pages, 2 figure
Control structures for high speed processors
A special processor was designed to function as a Reed Solomon decoder with throughput data rate in the Mhz range. This data rate is significantly greater than is possible with conventional digital architectures. To achieve this rate, the processor design includes sequential, pipelined, distributed, and parallel processing. The processor was designed using a high level language register transfer language. The RTL can be used to describe how the different processes are implemented by the hardware. One problem of special interest was the development of dependent processes which are analogous to software subroutines. For greater flexibility, the RTL control structure was implemented in ROM. The special purpose hardware required approximately 1000 SSI and MSI components. The data rate throughput is 2.5 megabits/second. This data rate is achieved through the use of pipelined and distributed processing. This data rate can be compared with 800 kilobits/second in a recently proposed very large scale integration design of a Reed Solomon encoder
Pairbreaking Without Magnetic Impurities in Disordered Superconductors
We study analytically the effects of inhomogeneous pairing interactions in
short coherence length superconductors, using a spatially varying
Bogoliubov-deGennes model. Within the Born approximation, it reproduces all of
the standard Abrikosov-Gor'kov pairbreaking and gaplessness effects, even in
the absence of actual magnetic impurities. For pairing disorder on a single
site, the T-matrix gives rise to bound states within the
BCS gap. Our results are compared with recent scanning tunneling microscopy
measurements on BiSrCaCuO with Zn or Ni impurities.Comment: 4 pages, 2 figures, submitted to PR
Impurity scattering in unconventional density waves: non-crossing approximation for arbitrary scattering rate
We present a detailed theoretical study on the thermodynamic properties of
impure quasi-one dimensional unconventional charge-, and spin-density waves in
the framework of mean-field theory. The impurities are of the ordinary
non-magnetic type. Making use of the full self-energy that takes into account
all ladder-, and rainbow-type diagrams, we are able to calculate the relevant
low temperature quantities for arbitrary impurity concentration and scattering
rates. These are the density of states, specific heat and the shift in the
chemical potential. Our results therefore cover the whole parameter space: they
include both the self-consistent Born and the resonant unitary limits, and most
importantly give exact results in between.Comment: 11 pages, 8 figure
Single and Pair Production of Doubly Charged Higgs Bosons at Hadron Colliders
Current searches for doubly charged Higgs bosons (H^{\pm\pm}) at the Fermilab
Tevatron are sensitive to single production of H^{\pm\pm}, although the pair
production mechanism q\bar q\to H^{++}H^{--} is assumed to be dominant. In the
context of a Higgs Triplet Model we study the mechanism q'\bar q\to
H^{\pm\pm}H^{\mp} at the Tevatron and CERN Large Hadron Collider, and show that
its inclusion can significantly improve the search potential for H^{\pm\pm}.
Moreover, assuming that the neutrino mass is generated solely by the triplet
field Yukawa coupling to leptons, we compare the branching ratios of
H^{\pm\pm}\to l^\pm l^\pm and H^{\pm\pm}\to H^\pm W^* for the cases of a normal
hierarchical, inverted hierarchical and degenerate neutrino mass spectrum.Comment: 17 pages, 15 figures, references added, version to appear in PR
Phytoplankton Community and Algal Toxicity at a Recurring Bloom in Sullivan Bay, Kabetogama Lake, Minnesota, USA
Kabetogama Lake in Voyageurs National Park, Minnesota, USA suffers from recurring late summer algal blooms that often contain toxin-producing cyanobacteria. Previous research identified the toxin microcystin in blooms, but we wanted to better understand how the algal and cyanobacterial community changed throughout an open water season and how changes in community structure were related to toxin production. Therefore, we sampled one recurring bloom location throughout the entire open water season. The uniqueness of this study is the absence of urban and agricultural nutrient sources, the remote location, and the collection of samples before any visible blooms were present. Through quantitative polymerase chain reaction (qPCR), we discovered that toxin-forming cyanobacteria were present before visible blooms and toxins not previously detected in this region (anatoxin-a and saxitoxin) were present, indicating that sampling for additional toxins and sampling earlier in the season may be necessary to assess ecosystems and human health risk
Formation of magnetic impurities and pair-breaking effect in a superfluid Fermi gas
We theoretically investigate a possible idea to introduce magnetic impurities
to a superfluid Fermi gas. In the presence of population imbalance
(, where is the number of Fermi atoms with
pseudospin ), we show that nonmagnetic potential
scatterers embedded in the system are magnetized in the sense that some of
excess -spin atoms are localized around them. They destroy the
superfluid order parameter around them, as in the case of magnetic impurity
effect discussed in the superconductivity literature. This pair-breaking effect
naturally leads to localized excited states below the superfluid excitation
gap. To confirm our idea in a simply manner, we treat an attractive Fermi
Hubbard model within the mean-field theory at T=0. We self-consistently
determine superfluid properties around a nonmagnetic impurity, such as the
superfluid order parameter, local population imbalance, as well as
single-particle density of states, in the presence of population imbalance.
Since the competition between superconductivity and magnetism is one of the
most fundamental problems in condensed matter physics, our results would be
useful for the study of this important issue in cold Fermi gases.Comment: 27 pages, 14 figure
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