1,844 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
Spin fluctuations and superconductivity in noncentrosymmetric heavy fermion systems CeRhSi and CeIrSi
We study the normal and the superconducting properties in noncentrosymmetric
heavy fermion superconductors CeRhSi and CeIrSi. For the normal state,
we show that experimentally observed linear temperature dependence of the
resistivity is understood through the antiferromagnetic spin fluctuations near
the quantum critical point (QCP) in three dimensions. For the superconducting
state, we derive a general formula to calculate the upper critical field
, with which we can treat the Pauli and the orbital depairing effect on
an equal footing. The strong coupling effect for general electronic structures
is also taken into account. We show that the experimentally observed features
in , the huge value up to 30(T), the downward
curvatures, and the strong pressure dependence, are naturally understood as an
interplay of the Rashba spin-orbit interaction due to the lack of inversion
symmetry and the spin fluctuations near the QCP. The large anisotropy between
and is explained in terms of
the spin-orbit interaction. Furthermore, a possible realization of the
Fulde-Ferrell- Larkin-Ovchinnikov state for is studied. We
also examine effects of spin-flip scattering processes in the pairing
interaction and those of the applied magnetic field on the spin fluctuations.
We find that the above mentioned results are robust against these effects. The
consistency of our results strongly supports the scenario that the
superconductivity in CeRhSi and CeIrSi is mediated by the spin
fluctuations near the QCP.Comment: 21pages, 13figures, to be published in Phys. Rev.
Let's Twist Again: General Metrics of G(2) Holonomy from Gauged Supergravity
We construct all complete metrics of cohomogeneity one G(2) holonomy with S^3
x S^3 principal orbits from gauged supergravity. Our approach rests on a
generalization of the twisting procedure used in this framework. It corresponds
to a non-trivial embedding of the special Lagrangian three-cycle wrapped by the
D6-branes in the lower dimensional supergravity. There are constraints that
neatly reduce the general ansatz to a six functions one. Within this approach,
the Hitchin system and the flop transformation are nicely realized in eight
dimensional gauged supergravity.Comment: 31 pages, latex; v2: minor changes, references adde
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
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
Multi-Instanton Calculus and Equivariant Cohomology
We present a systematic derivation of multi-instanton amplitudes in terms of
ADHM equivariant cohomology. The results rely on a supersymmetric formulation
of the localization formula for equivariant forms. We examine the cases of N=4
and N=2 gauge theories with adjoint and fundamental matter.Comment: 29 pages, one more reference adde
Microscopic Mechanism and Pairing Symmetry of Superconductivity in the Noncentrosymmetric Heavy Fermion Systems CeRhSI and CeIrSi
We study the pairing symmetry of the noncentrosymmetric heavy fermion
superconductors CeRhSi and CeIrSi under pressures, which are both
antiferromagnets at ambient pressure. We solve the Eliashberg equation by means
of the random phase approximation and find that the mixed state of extended
s-wave and p-wave rather than the wave state could be realized by
enhanced antiferromagnetic spin fluctuations. It is elucidated that the gap
function has line nodes on the Fermi surface and the resulting density of state
in the superconducting state shows a similar character to that of usual d-wave
superconductors, resulting in the NMR relaxation rate that exhibits
no coherence peak and behaves like at low temperatures
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
Emergent Nodal Excitations due to the Coexistence of Superconductivity and Antiferromagnetism: Cases with and without Inversion Symmetry
We argue the emergence of nodal excitations due to the coupling with static
antiferromagnetic order in fully-gapped superconducting states in both cases
with and without inversion symmetry. This line node structure is not
accompanied with the sign change of the superconducting gap, in contrast to
usual unconventional Cooper pairs with higher angular momenta. In the case
without inversion symmetry, the stability of the nodal excitations crucially
depends on the direction of the antiferromagnetic staggered magnetic moment. A
possible realization of this phenomenon in CePtSi is discussed.Comment: 4 pages, 7 figure
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