2,703 research outputs found
Current in narrow channels of anisotropic superconductors
We argue that in channels cut out of anisotropic single crystal
superconductors and narrow on the scale of London penetration depth, the
persistent current must cause the transverse phase difference provided the
current does not point in any of the principal crystal directions. The
difference is proportional to the current value and depends on the anisotropy
parameter, on the current direction relative to the crystal, and on the
transverse channel dimension. An experimental set up to measure the transverse
phase is proposed.Comment: 3 pages, 1 figur
On details of the thermodynamical derivation of the Ginsburg--Landau equations
We examine the procedure of thermodynamical derivation of the
Ginsburg--Landau equation for current, which is given unclear and contradictory
interpretations in existing textbooks. We clarify all steps of this procedure
and find as a consequence a limitation on the validity range of the
thermodynamic Ginsburg--Landau theory, which does not seem to be explicitely
stated up to now: we conclude that the thermodynamic theory is applicable only
to a superconducting specimen that is not a part of an external
current-carrying loop.Comment: 11 pages. Accepted for publication in 'Superconductor Science and
Technology
Field-dependent diamagnetic transition in magnetic superconductor
The magnetic penetration depth of single crystal
was measured down to 0.4 K in dc fields up
to 7 kOe. For insulating , Sm spins order at the
N\'{e}el temperature, K, independent of the applied field.
Superconducting ( K) shows a
sharp increase in diamagnetic screening below which varied from
4.0 K () to 0.5 K ( 7 kOe) for a field along the c-axis. If the
field was aligned parallel to the conducting planes, remained
unchanged. The unusual field dependence of indicates a spin freezing
transition that dramatically increases the superfluid density.Comment: 4 pages, RevTex
Evaluating free flux flow in low-pinning molybdenum-germanium superconducting films
Vortex dynamics in molybdenum-germanium superconducting films were found to
well approximate the unpinned free limit even at low driving forces. This
provided an opportunity to empirically establish the intrinsic character of
free flux flow and to test in detail the validity of theories for this regime
beyond the Bardeen-Stephen approximation. Our observations are in good
agreement with the mean-field result of time dependent Ginzburg-Landau theory.
PACS: 74.25.Sv,74.25.Wx,74.25.Uv,74.25.Op,74.25.F- Keywords: vortices,
fluxon, Larkin, Ovchinnikov, upper critical magnetic fieldComment: This is the final revised version of a paper that is currently in
press. It is expected to appear in Phys. Rev. B in 201
Solitary wave complexes in two-component mixture condensates
Axisymmetric three-dimensional solitary waves in uniform two-component
mixture Bose-Einstein condensates are obtained as solutions of the coupled
Gross-Pitaevskii equations with equal intracomponent but varying intercomponent
interaction strengths. Several families of solitary wave complexes are found:
(1) vortex rings of various radii in each of the components, (2) a vortex ring
in one component coupled to a rarefaction solitary wave of the other component,
(3) two coupled rarefaction waves, (4) either a vortex ring or a rarefaction
pulse coupled to a localised disturbance of a very low momentum. The continuous
families of such waves are shown in the momentum-energy plane for various
values of the interaction strengths and the relative differences between the
chemical potentials of two components. Solitary wave formation, their stability
and solitary wave complexes in two-dimensions are discussed.Comment: 4 pages, 2 figures, 2 table
Spatial and Temporal Noise Spectra of Spatially Extended Systems with Order-Disorder Phase Transitions
The noise power spectra of spatially extended dynamical systems are
investigated, using as a model the Complex Ginzburg-Landau equation with a
stochastic term. Analytical and numerical investigations show that the spatial
spectra of the ordered state are similar to Bose-Einstein distribution, showing
1/k^2 asymptotics in the long wavelength limit. The temporal noise spectra of
the ordered state are obtained of 1/^alpha form, where alpha=2-D/2 with D the
spatial dimension of the system.Comment: to be printed in International Journal of Bifurcation and Chao
Origin of Orthorhombic Transition, Magnetic Transition, and Shear Modulus Softening in Iron Pnictide Superconductors: Analysis based on the Orbital Fluctuation Theory
The main features in iron-pnictide superconductors are summarized as (i) the
orthorhombic transition accompanied by remarkable softening of shear modulus,
(ii) high-Tc superconductivity close to the orthorhombic phase, and (iii)
stripe-type magnetic order induced by orthorhombicity. To present a unified
explanation for them, we analyze the multiorbital Hubbard-Holstein model with
Fe-ion optical phonons based on the orbital fluctuation theory. In the
random-phase-approximation (RPA), a small electron-phonon coupling constant
() is enough to produce large orbital (=charge quadrupole)
fluctuations. The most divergent susceptibility is the
-antiferro-quadrupole (AFQ) susceptibility, which causes the s-wave
superconductivity without sign reversal (s_{++}-wave state). At the same time,
divergent development of -ferro-quadrupole (FQ) susceptibility is
brought by the "two-orbiton process" with respect to the AFQ fluctuations,
which is absent in the RPA. The derived FQ fluctuations cause the softening of
shear modulus, and its long-range-order not only triggers the
orthorhombic structure transition, but also induces the instability of
stripe-type antiferro-magnetic state. In other words, the condensation of
composite bosons made of two orbitons gives rise to the FQ order and structure
transition. The theoretically predicted multi-orbital-criticality presents a
unified explanation for abovementioned features of iron pnictide
superconductors.Comment: 19 pages, 15 figure
Motion and homogenization of vortices in anisotropic Type II superconductors
The motion of vortices in an anisotropic superconductor is considered. For a system of well-separated vortices, each vortex is found to obey a law of motion analogous to the local induction approximation, in which velocity of the vortex depends upon the local curvature and orientation. A system of closely packed vortices is then considered, and a mean field model is formulated in which the individual vortex lines are replaced by a vortex density
Single Leptoquark Production at and Colliders
We consider single production of leptoquarks (LQ's) at and
colliders, for two values of the centre-of-mass energy,
GeV and 1 TeV. We find that LQ's which couple within the first
generation are observable for LQ masses almost up to the kinematic limit, both
at and colliders, for the LQ coupling strength equal to
. The cross sections for single production of - and
-generation LQ's at colliders are too small to be observable.
In collisions, on the other hand, -generation LQ's with
masses much larger than can be detected. However,
-generation LQ's can be seen at colliders only for
masses at most , making their observation more probable via the
pair production mechanism.Comment: plain TeX, 14 pages, 6 figures (not included but available on
request), some minor changes to the text, one reference added, figures and
conclusions unchanged, UdeM-LPN-TH-93-152, McGill-93/2
Observation of Coherently-Enhanced Tunable Narrow-Band Terahertz Transition Radiation from a Relativistic Sub-Picosecond Electron Bunch Train
We experimentally demonstrate the production of narrow-band (% at THz) THz transition radiation with tunable
frequency over [0.37, 0.86] THz. The radiation is produced as a train of
sub-picosecond relativistic electron bunches transits at the vacuum-aluminum
interface of an aluminum converter screen. We also show a possible application
of modulated beams to extend the dynamical range of a popular bunch length
diagnostic technique based on the spectral analysis of coherent radiation.Comment: 3 pages, 6 figure
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