435 research outputs found
Derivation of the superconducting gap equation for the noncentrosymmetric superconductor Li2Pt3B
We present here the mathematical background of our approach, presented in
Phys. Rev. B 86, 134526 (2012) regarding the gap function and symmetry for the
noncentrosymmetric (NCS) superconductor . As revealed by the
experiment, this NCS superconductor gives rise to line nodes in the
superconducting order parameter, which is responsible for many of its
experimental behaviors. Owing to the enhanced d-character of the relevant bands
that cross the Fermi level,the system gets weakly correlated. The nature and
symmetry of this nodal behavior is explained from a microscopic viewpoint. In
this article starting with an Hubbard model relevant for this NCS system by
considering the effect of the onsite Coulomb repulsion on the pairing potential
perturbatively, we extract the superconducting gap equation. Further analysis
of this equation predicts a wave gap function with line nodes as the
most promising candidate in the superconducting state.Comment: 7 pages, Proceeding versio
Ginzburg-Landau theory of noncentrosymmetric superconductors
The data of temperature dependent superfluid density in
LiPdB and LiPtB [Yuan {\it et al.}, \phrl97, 017006 (2006)]
show that a sudden change of the slope of occur at slightly lower
than the critical temperature. Motivated by this observation, we
microscopically derive the Ginzburg-Landau (GL) equations for
noncentrosymmetric superconductors with Rashba type spin orbit interaction.
Cooper pairing is assumed to occur between electrons only in the same spin
split band and pair scattering is allowed to occur between two spin split
bands. The GL theory of such a system predicts two transition temperatures, the
higher of which is the conventional critical temperature while the lower
one corresponds to the cross-over from a mixed singlet-triplet phase at
lower temperatures to only spin-singlet or spin-triplet (depending on the sign
of the interband scattering potential) phase at higher temperatures. As a
consequence, shows a kink at this cross-over temperature. We
attribute the temperature at which sudden change of slope occurs in the
observed to the temperature . This may also be associated with
the observed kink in the penetration depth data of CePtSi. We have also
estimated critical field near critical temperature.Comment: 7 pages, 1 figur
Manifestation of helical edge states as zero-bias magneto-tunneling-conductance peaks in non-centrosymmetric superconductors
Helical edge states exist in the mixed spin-singlet and -triplet phase of a
noncentrosymmetric superconductor (NCSS) when the pair amplitude (PA) in the
negative helicity band, , is smaller than the PA in the positive
helicity band, , i.e., when the PA in the triplet component is more
than the same in the singlet component. We numerically determine energies of
these edge states as a function of . The presence
of these edge states is reflected in the tunneling process from a normal metal
to an NCSS across a bias energy : (i) Angle resolved spin conductance (SC)
obeying the symmetry shows peaks when the bias energy
equals the available quasiparticle edge state energy provided . (ii) The total SC, , is zero but modulates with for finite
magnetic field . (iii) The zero bias peaks of and total charge
conductance, , at finite split into two at finite for moderate
. (iv) At zero bias, and increase with and show peaks at
where is a characteristic field.Comment: minor changes; one figure is adde
Spin analog of the controlled Josephson charge current
We propose a controlled Josephson spin current across the junction of two
non-centrosymmetric superconductors like CePt_3Si. The Josephson spin current
arises due to direction dependent tunneling matrix element and different
momentum dependent phases of the triplet components of the gap function. Its
modulation with the angle \xi between the noncentrosymmetric axes of two
superconductors is proportional to \sin \xi. This particular dependence on \xi
may find application of the proposed set-up in making a Josephson spin switch.Comment: 4 pages, 1 figure; title is changed; article is rewritte
Upper limits on gravitational wave emission from 78 radio pulsars
We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO 600 gravitational wave detectors. The data from both runs have been combined coherently to maximize sensitivity. For the first time, pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor of 10. For example, our tightest upper limit on the gravitational strain is 2.6×10−25 for PSR J1603−7202, and the equatorial ellipticity of PSR J2124–3358 is less than 10−6. Furthermore, our strain upper limit for the Crab pulsar is only 2.2 times greater than the fiducial spin-down limit
Search of S3 LIGO data for gravitational wave signals from spinning black hole and neutron star binary inspirals
We report on the methods and results of the first dedicated search for gravitational waves emitted during the inspiral of compact binaries with spinning component bodies. We analyze 788 hours of data collected during the third science run (S3) of the LIGO detectors. We searched for binary systems using a detection template family specially designed to capture the effects of the spin-induced precession of the orbital plane. We present details of the techniques developed to enable this search for spin-modulated gravitational waves, highlighting the differences between this and other recent searches for binaries with nonspinning components. The template bank we employed was found to yield high matches with our spin-modulated target waveform for binaries with masses in the asymmetric range 1.0M
Upper Limits on a Stochastic Background of Gravitational Waves
The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of Ω
All-sky search for periodic gravitational waves in LIGO S4 data
We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50–1000 Hz and with the frequency’s time derivative in the range −1×10−8 Hz s−1 to zero. Data from the fourth LIGO science run (S4) have been used in this search. Three different semicoherent methods of transforming and summing strain power from short Fourier transforms (SFTs) of the calibrated data have been used. The first, known as StackSlide, averages normalized power from each SFT. A “weighted Hough” scheme is also developed and used, which also allows for a multi-interferometer search. The third method, known as PowerFlux, is a variant of the StackSlide method in which the power is weighted before summing. In both the weighted Hough and PowerFlux methods, the weights are chosen according to the noise and detector antenna-pattern to maximize the signal-to-noise ratio. The respective advantages and disadvantages of these methods are discussed. Observing no evidence of periodic gravitational radiation, we report upper limits; we interpret these as limits on this radiation from isolated rotating neutron stars. The best population-based upper limit with 95% confidence on the gravitational-wave strain amplitude, found for simulated sources distributed isotropically across the sky and with isotropically distributed spin axes, is 4.28×10−24 (near 140 Hz). Strict upper limits are also obtained for small patches on the sky for best-case and worst-case inclinations of the spin axes
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