6,992 research outputs found
Quasiparticle Interactions in Two and Three Dimensional Superconductors
I investigate the difference between the quasiparticle properties in two
dimensional(2D)and three dimensional(3D) s-wave superconductors. Using the
original BCS model for the pairing interaction and direct Coulomb interaction I
show that quasiparticle interactions lead to a stronger energy dependence in
the single-particle self-energies in 2D than in 3D superconductors. This
difference arises from the presence of the low lying collective mode of the
order parameter in the 2D case which ensures that oscillator strength in the
response function is at low frequencies, . This strong
quantitative difference between 2D and 3D superconductors points to the
importance of treating quasiparticle interactions in low dimensional
superconductors rather than assuming that renormalizations remain unchanged
from the normal state.Comment: version of original paper accepted for publication in Europhysics
Letter
RURAL DEVELOPMENT POLICY AND BALANCED NATIONAL GROWTH
Community/Rural/Urban Development,
DISCUSSION: SOUTHERN AGRICULTURE IN AN ERA OF EXPANDING EXPORTS
International Relations/Trade,
THE ROLE OF FOOD IN THE INTERNATIONAL AFFAIRS OF THE UNITED STATES
International Relations/Trade,
Strong-Coupling Features Due to Quasiparticle Interaction in Two Dimensional Superconductors
I calculate the effect of interactions among superconducting quasiparticles
in two-dimensional(2D) a superconductor at T=0. The strength of the effective
interaction among the quasiparticles is essentially given by the screened
Coulomb interaction which has strength at low frequency because of the gapless
nature of the plasmon. This is in contrast to three dimensions where the
effective interaction has negligible weight at frequencies , the
superconducting gap. The quasiparticle interactions give rise to
strong-coupling effects in experimental quantities which are beyond the
conventional Eliashberg treatment of superconductivity. The present calculation
offers an explanation of why these effects are much larger in 2D than in 3D
superconductors and, in particular, why the analogous strong-coupling effects
due to quasiparticle interactions are seen in data on the quasi-2D cuprate
superconductors. the strong-coupling features seen in data on the cuprates are
discussed in light of the present calculation.Comment: 18 pages including 11 figures Revte
Spin Dynamics of a Canted Antiferromagnet in a Magnetic Field
The spin dynamics of a canted antiferromagnet with a quadratic spin-wave
dispersion near \vq =0 is shown to possess a unique signature. When the
anisotropy gap is negligible, the spin-wave stiffness \dsw (\vq, B) =
(\omega_{\vq}-B)/q^2 depends on whether the limit of zero field or zero
wavevector is taken first. Consequently, \dsw is a strong function of
magnetic field at a fixed wavevector. Even in the presence of a sizeable
anisotropy gap, the field dependence of both \dsw and the gap energy
distinguishes a canted antiferromagnet from a phase-separated mixture
containing both ferromagnetic and antiferromagnetic regions.Comment: 10 pages, 3 figure
Searching for jet rotation in Class 0/I sources observed with GEMINI/GNIRS.
Original article can be found at: http://www.aanda.org/
Copyright The European Southern ObservatoryContext: In recent years, there has been a number of detections of gradients in the radial velocity profile across jets from young stars. The significance of these results is considerable. They may be interpreted as a signature of jet rotation about its symmetry axis, thereby representing the only existing observational indications supporting the theory that jets extract angular momentum from star-disk systems. However, the possibility that we are indeed observing jet rotation in pre-main sequence systems is undergoing active debate.
Aims: To test the validity of a rotation argument, we must extend the survey to a larger sample, including younger sources.
Methods: We present the latest results of a radial velocity analysis on jets from Class 0 and I sources, using high resolution data from the infrared spectrograph GNIRS on GEMINI South. We obtained infrared spectra of protostellar jets HH 34, HH 111-H, HH 212 NK1 and SK1.
Results: The [Fe II] emission was unresolved in all cases and so Doppler shifts across the jet width could not be accessed. The H2 emission was resolved in all cases except HH 34. Doppler profiles across the molecular emission were obtained, and gradients in radial velocity of typically 3 km s-1 identified.
Conclusions: Agreement with previous studies implies they may be interpreted as jet rotation, leading to toroidal velocity and angular momentum flux estimates of 1.5 km s-1 and 1 × 10-5 yr-1 AU km s-1 respectively. However, caution is needed. For example, emission is asymmetric across the jets from HH 212 suggesting a more complex interpretation is warranted. Furthermore, observations for HH 212 and HH 111-H are conducted far from the source implying external influences are more likely to confuse the intrinsic flow kinematics. These observations demonstrate the difficulty of conducting this study from the ground, and highlight the necessity for high angular resolution via adaptive optics or space-based facilities
Extreme ultraviolet emission lines of Ni XII in laboratory and solar spectra
Wavelengths for emission lines arising from 3s23p5-3s3p6 and 3s23p5-3s23p43d transitions in Ni XII have been measured in extreme ultraviolet spectra of the Joint European Torus(JET) tokamak. The 3s23p5 2P1/2-3s23p4(3P)3d 2D3/2 line is found to lie at 152.90 ± 0.02 A, a significant improvement over the previous experimental determination of 152.95 ± 0.5 A. This new wavelength is in good agreement with a solar identification at 152.84 ± 0.06 A, confirming the presence of this line in the solar spectrum. The Ni XII feature at 152.15 A may be a result only of the 3s23p5 2P3/2-3s23p4(3P)3d 2D5/2 transition, rather than a blend of this line with 3s23p5 2P3/2-3s23p (3P)3d 2P1/2, as previously suggested. Unidentified emission
lines at 295.32 and 317.61 A in solar flare spectra from the Skylab mission are tentatively identified as the 3s23p5 2P3/2-3s3p6 2S1/2 and 3s23p5 2P1/2-3s3p6 2S1/2 transitions in Ni XII, which have laboratory wavelengths of 295.33 and 317.50 A, respectively. Additional support for these identifications is provided by the line intensity ratio for the solar features, which shows good agreement between theory and observation
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