3,951 research outputs found

### Magnetic field dependence of pairing interaction in ferromagnetic superconductors with triplet pairing

It is developed a microscopic description of superconductivity in
ferromagnetic materials with triplet pairing triggered by the exchange of
magnetic fluctuations. Instead widely used paramagnon model we work with
phenomenological spectrum of fluctuations in the orthorhombic ferromagnet with
strong magnetic anisotropy. Depending of the field orientation parallel or
perpendicular to the direction of spontaneous magnetization the effective
amplitude of pairing interaction proves to be decreasing or increasing function
of magnetic field that allows to explain the drastic difference in magnitudes
of upper critical field in these directions.Comment: 9 pages, no figure

### Paramagnetic limit of superconductivity in a crystal without inversion center

The theory of paramagnetic limit of superconductivity in metals without
inversion center is developed. There is in general the paramagnetic suppression
of superconducting state. The effect is strongly dependent on field orientation
in respect to crystal axes. The reason for this is that the degeneracy of
electronic states with opposite momenta forming of Cooper pairs is lifted by
magnetic field but for some field directions this lifting can be small or even
absent.Comment: 9 pages, no figure

### Long sandwich modules for photon veto detectors

Long lead-scintillator sandwich modules developed for the BNL experiment
KOPIO are described. The individual 4 m long module consists of 15 layers of 7
mm thick extruded scintillator and 15 layers of 1 mm lead absorber. Readout is
implemented via WLS fibers glued into grooves in a scintillator with 7 mm
spacing and viewed from both ends by the phototubes. Time resolution of 300 ps
for cosmic MIPs was obtained. Light output stability monitored for 2 years
shows no degradation beyond the measurement errors. A 4 m long C-bent sandwich
module was also manufactured and tested.Comment: 14 pages, 13 figures, 1 tabl

### Helical vortex phase in the non-centrosymmetric CePt_3Si

We consider the role of magnetic fields on the broken inversion
superconductor CePt_3Si. We show that upper critical field for a field along
the c-axis exhibits a much weaker paramagnetic effect than for a field applied
perpendicular to the c-axis. The in-plane paramagnetic effect is strongly
reduced by the appearance of helical structure in the order parameter. We find
that to get good agreement between theory and recent experimental measurements
of H_{c2}, this helical structure is required. We propose a Josephson junction
experiment that can be used to detect this helical order. In particular, we
predict that Josephson current will exhibit a magnetic interference pattern for
a magnetic field applied perpendicular to the junction normal. We also discuss
unusual magnetic effects associated with the helical order.Comment: 5 pages, 2 figures, Accepted as Phys Rev. Lette

### Self-similarity in Laplacian Growth

We consider Laplacian Growth of self-similar domains in different geometries.
Self-similarity determines the analytic structure of the Schwarz function of
the moving boundary. The knowledge of this analytic structure allows us to
derive the integral equation for the conformal map. It is shown that solutions
to the integral equation obey also a second order differential equation which
is the one dimensional Schroedinger equation with the sinh inverse square
potential. The solutions, which are expressed through the Gauss hypergeometric
function, characterize the geometry of self-similar patterns in a wedge. We
also find the potential for the Coulomb gas representation of the self-similar
Laplacian growth in a wedge and calculate the corresponding free energy.Comment: 16 pages, 9 figure

### Low-$T$ Phononic Thermal Conductivity in Superconductors with Line Nodes

The phonon contribution to the thermal conductivity at low temperature in
superconductors with line nodes is calculated assuming that scattering by both
nodal quasiparticles and the sample boundaries is significant. It is determined
that, within the regime in which the quasiparticles are in the universal limit
and the phonon attenuation is in the hydrodynamic limit, there exists a wide
temperature range over which the phonon thermal conductivity varies as $T^2$.
This behaviour comes from the fact that transverse phonons propagating along
certain directions do not interact with nodal quasiparticles and is thus found
to be required by the symmetry of the crystal and the superconducting gap,
independent of the model used for the electron-phonon interaction. The
$T^2$-dependence of the phonon thermal conductivity occurs over a well-defined
intermediate temperature range: at higher $T$ the temperature-dependence is
found to be linear while at lower $T$ the usual $T^3$ (boundary-limited)
behaviour is recovered. Results are compared to recent measurements of the
thermal conductivity of Tl2201, and are shown to be consistent with the data.Comment: 4 page

### De Haas-van Alphen effect in two- and quasi two-dimensional metals and superconductors

An analytical form of the quantum magnetization oscillations (de Haas-van
Alphen effect) is derived for two- and quasi two-dimensional metals in normal
and superconducting mixed states. The theory is developed under condition that
the chemical potential is much greater than the cyclotron frequency, which is
proved to be valid for using grand canonical ensemble in the systems of low
dimensionality. Effects of impurity, temperature, spin-splitting and vortex
lattice - in the case of superconductors of type II -, are taken into account.
Contrary to the three dimensional case, the oscillations in sufficiently pure
systems of low dimensionality and at sufficiently low temperatures are
characterized by a saw-tooth wave form, which smoothened with temperature and
concentration of impurities growth. In the normal quasi two-dimensional
systems, the expression for the magnetization oscillations includes an extra
factor expressed through the transfer integral between the layers. The
additional damping effect due to the vortex lattice is found. The criterion of
proximity to the upper critical field for the observation of de Haas-van Alphen
effect in the superconducting mixed state is established.Comment: 18 pages, Latex, revised versio

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