929 research outputs found
Nodeless superconductivity in the cage-type superconductor Sc5Ru6Sn18 with preserved time-reversal symmetry
We report the single-crystal synthesis and detailed investigations of the
cage-type superconductor Sc5Ru6Sn18, using powder x-ray diffraction (XRD),
magnetization, specific-heat and muon-spin relaxation (muSR) measurements.
Sc5Ru6Sn18 crystallizes in a tetragonal structure (space group I41/acd) with
the lattice parameters a = 1.387(3) nm and c = 2.641(5) nm. Both DC and AC
magnetization measurements prove the type-II superconductivity in Sc5Ru6Sn18
with Tc = 3.5(1) K, a lower critical field H_c1 (0) = 157(9) Oe and an upper
critical field, H_c2 (0) = 26(1) kOe. The zero-field electronic specific-heat
data are well fitted using a single-gap BCS model, with superconducting gap =
0.64(1) meV. The Sommerfeld constant varies linearly with the applied magnetic
field, indicating s-wave superconductivity in Sc5Ru6Sn18. Specific-heat and
transverse-field (TF) muSR measurements reveal that Sc5Ru6Sn18 is a
superconductor with strong electron-phonon coupling, with TF-muSR also
suggesting the single-gap s-wave character of the superconductivity.
Furthermore, zero-field muSR measurements do not detect spontaneous magnetic
fields below Tc, hence implying that time-reversal symmetry is preserved in
Sc5Ru6Sn18.Comment: 23 pages, 11 figure
Quantum Melting of the Charge Density Wave State in 1T-TiSe2
We report a Raman scattering study of low-temperature, pressure-induced
melting of the CDW phase of 1T-TiSe2. Our Raman scattering measurements reveal
that the collapse of the CDW state occurs in three stages: (i) For P<5 kbar,
the pressure dependence of the CDW amplitude mode energies and intensities are
indicative of a ``crystalline'' CDW regime; (ii) for 5 < P < 25 kbar, there is
a decrease in the CDW amplitude mode energies and intensities with increasing
pressure that suggests a regime in which the CDW softens, and may decouple from
the lattice; and (iii) for P>25 kbar, the absence of amplitude modes reveals a
melted CDW regime.Comment: 5 pages, 4 figure
Galois theory and commutators
We prove that the relative commutator with respect to a subvariety of a
variety of Omega-groups introduced by the first author can be described in
terms of categorical Galois theory. This extends the known correspondence
between the Froehlich-Lue and the Janelidze-Kelly notions of central extension.
As an example outside the context of Omega-groups we study the reflection of
the category of loops to the category of groups where we obtain an
interpretation of the associator as a relative commutator.Comment: 14 page
Non-Abelian Monopole and Dyon Solutions in a Modified Einstein-Yang-Mills-Higgs System
We have studied a modified Yang-Mills-Higgs system coupled to Einstein
gravity. The modification of the Einstein-Hilbert action involves a direct
coupling of the Higgs field to the scalar curvature. In this modified system we
are able to write a Bogomol'nyi type condition in curved space and demonstrate
that the positive static energy functional is bounded from below. We then
investigate non-Abelian sperically symmetric static solutions in a similar
fashion to the `t Hooft-Polyakov monopole. After reviewing previously studied
monopole solutions of this type, we extend the formalism to included electric
charge and we present dyon solutions.Comment: 18 pages LaTeX, 7 eps-figure
Gravitating dyons and the Lue-Weinberg bifurcation
Gravitating t'Hooft-Polyakov magnetic monopoles can be constructed when
coupling the Georgi-Glashow model to gravitation. For a given value of the
Higgs boson mass, these gravitating solitons exist up to a critical value of
the ratio of the vector meson mass to the Planck mass. The critical solution is
characterized by a degenerate horizon of the metric. As pointed out recently by
Lue and Weinberg, two types of critical solutions can occur, depending on the
value of the Higgs boson mass. Here we investigate this transition for dyons
and show that the Lue and Weinberg phenomenon is favorized by the presence of
the electric-charge degree of freedom.Comment: RevTeX, 6 pages, 8 figure
Scaling of Star Polymers with one to 80 Arms
We present large statistics simulations of 3-dimensional star polymers with
up to arms, and with up to 4000 monomers per arm for small values of
. They were done for the Domb-Joyce model on the simple cubic lattice. This
is a model with soft core exclusion which allows multiple occupancy of sites
but punishes each same-site pair of monomers with a Boltzmann factor . We
use this to allow all arms to be attached at the central site, and we use the
`magic' value to minimize corrections to scaling. The simulations are
made with a very efficient chain growth algorithm with resampling, PERM,
modified to allow simultaneous growth of all arms. This allows us to measure
not only the swelling (as observed from the center-to-end distances), but also
the partition sum. The latter gives very precise estimates of the critical
exponents . For completeness we made also extensive simulations of
linear (unbranched) polymers which give the best estimates for the exponent
.Comment: 7 pages, 7 figure
Parity Violating Gravitational Coupling Of Electromagnetic Fields
A manifestly gauge invariant formulation of the coupling of the Maxwell
theory with an Einstein Cartan geometry is given, where the space time torsion
originates from a massless Kalb-Ramond field augmented by suitable U(1) Chern
Simons terms.We focus on the situation where the torsion violates parity, and
relate it to earlier proposals for gravitational parity violation.Comment: 7 Pages, Latex . no figures, Replaced with Revtex version, many
references added and typos correcte
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