2,498 research outputs found
NMR relaxation rate in non-centrosymmetric superconductors
The spin-lattice relaxation rate of nuclear magnetic resonance in a clean
superconductor without inversion center is calculated for arbitrary pairing
symmetry and band structure, in the presence of strong spin-orbit coupling.Comment: 4 page
Signature of superconducting states in cubic crystal without inversion symmetry
The effects of absence of inversion symmetry on superconducting states are
investigated theoretically. In particular we focus on the noncentrosymmetric
compounds which have the cubic symmetry like LiPtB. An appropriate
and isotropic spin-orbital interaction is added in the Hamiltonian and it acts
like a magnetic monopole in the momentum space. The consequent pairing
wavefunction has an additional triplet component in the pseudospin space, and a
Zeeman magnetic field can induce a collinear supercurrent
with a coefficient . The effects of anisotropy embedded in the cubic
symmetry and the nodal superconducting gap function on are also
considered. From the macroscopic perspectives, the pair of mutually induced
and magnetization can affect the distribution of magnetic
field in such noncentrosymmetric superconductors, which is studied through
solving the Maxwell equation in the Meissner geometry as well as the case of a
single vortex line. In both cases, magnetic fields perpendicular to the
external ones emerge as a signature of the broken symmetry.Comment: 16 pages in pre-print forma
Phases of dual superconductivity and confinement in softly broken N=2 supersymmetric Yang-Mills theories
We study the electric flux tubes that undertake color confinement in N=2
supersymmetric Yang-Mills theories softly broken down to N=1 by perturbing with
the first two Casimir operators. The relevant Abelian Higgs model is not the
standard one due to the presence of an off-diagonal coupling among different
magnetic U(1) factors. We perform a preliminary study of this model at a
qualitative level. BPS vortices are explicitely obtained for particular values
of the soft breaking parameters. Generically however, even in the ultrastrong
scaling limit, vortices are not critical but live in a "hybrid" type II phase.
Also, ratios among string tensions are seen to follow no simple pattern. We
examine the situation at the half Higgsed vacua and find evidence for solutions
with the behaviour of superconducting strings. In some cases they are solutions
to BPS equations.Comment: 15 pages, 1 figure, revtex; v2: typos corrected, final versio
On the spin susceptibility of noncentrosymmetric superconductors
We calculate the spin susceptibility of a superconductor without inversion
symmetry, both in the clean and disordered cases. The susceptibility has a
large residual value at zero temperature, which is further enhanced in the
presence of scalar impurities.Comment: 12 pages, 3 figure
Supersymmetric Electroweak Cosmic Strings
We study the connection between supersymmetry and a topological bound
in a two-Higgs-doublet system with an gauge group. We derive the Bogomol'nyi equations from
supersymmetry considerations showing that they hold provided certain conditions
on the coupling constants, which are a consequence of the huge symmetry of the
theory, are satisfied. Their solutions, which can be interpreted as electroweak
cosmic strings breaking one half of the supersymmetries of the theory, are
studied. Certain interesting limiting cases of our model which have recently
been considered in the literature are finally analyzed.Comment: 20 pages, RevTe
Holography and Unquenched Quark-Gluon Plasmas
We employ the string/gauge theory correspondence to study properties of
strongly coupled quark-gluon plasmas in thermal gauge theories with a large
number of colors and flavors. In particular, we analyze non-critical string
duals of conformal (S)QCD, as well as ten dimensional wrapped fivebrane duals
of SQCD-like theories. We study general properties of the dual plasmas,
including the drag force exerted on a probe quark and the jet quenching
parameter. We find that these plasma observables depend on the number of colors
and flavors in the ``QCD dual''; in particular, we find that the jet quenching
parameter increases linearly with N_f/N_c at leading order in the probe limit.
In the ten dimensional case we find a non trivial drag coefficient but a
vanishing jet quenching parameter. We comment on the relation of this result
with total screening and argue that the same features are shared by all known
plasmas dual to fivebranes in ten dimensions. We also construct new D5 black
hole solutions with spherical horizon and show that they exhibit the same
features.Comment: 30 pages. v2: Comments in section 2 and references updated, a typo
fixe
Topological quantum field theory and four-manifolds
I review some recent results on four-manifold invariants which have been
obtained in the context of topological quantum field theory. I focus on three
different aspects: (a) the computation of correlation functions, which give
explicit results for the Donaldson invariants of non-simply connected
manifolds, and for generalizations of these invariants to the gauge group
SU(N); (b) compactifications to lower dimensions, and relations with
three-manifold topology and with intersection theory on the moduli space of
flat connections on Riemann surfaces; (c) four-dimensional theories with
critical behavior, which give some remarkable constraints on Seiberg-Witten
invariants and new results on the geography of four-manifolds.Comment: 10 pages, LaTeX. Talk given at the 3rd ECM, Barcelona, July 2000;
references adde
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
Effects of impurities on Hc2(T) in superconductors without inversion symmetry
We calculate the upper critical field, Hc2(T), due to the orbital pair
breaking in disordered superconductors without inversion symmetry. Differences
from the usual centrosymmetric case are highlighted. The linearized gap
equations in magnetic field, with the singlet and triplet pairing channels
mixed by impurity scattering, are solved exactly for a cubic crystal.Comment: 11 pages, 1 figur
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