191 research outputs found
Electromagnetic Response of a Superconductor: Effect of Order Parameter Collective Modes
Effects of order parameter collective modes on electromagnetic response are
studied for a clean spin-triplet superconductor with orbital
symmetry, which has been proposed as a candidate pairing symmetry for
SrRuO. It is shown that the superconductor has
characteristic massive collective modes analogous to the clapping mode in the
A-phase of superfluid He. We discuss the contribution from the collective
modes to ultrasound attenuation and electromagnetic absorption. We show that in
the electromagnetic absorption spectrum the clapping mode gives rise to a
resonance peak well below the pair breaking frequency, while the ultrasound
attenuation is hardly influenced by the collective excitations.Comment: 4 pages RevTex, 1 eps figur
Light Quark Masses with an O(a)-Improved Action
We present the recent Fermilab calculations of the masses of the light
quarks, using tadpole-improved Sheikholeslami-Wohlert (SW) quarks. Various
sources of systematic errors are studied. Our final result for the average
light quark mass in the quenched approximation evaluated in the
scheme is .Comment: 3 pgs. 3 figures. espcrc2.sty included. Talk presented at
LATTICE96(phenomenology
Anisotropy in the Antiferromagnetic Spin Fluctuations of Sr2RuO4
It has been proposed that Sr_2RuO_4 exhibits spin triplet superconductivity
mediated by ferromagnetic fluctuations. So far neutron scattering experiments
have failed to detect any clear evidence of ferromagnetic spin fluctuations
but, instead, this type of experiments has been successful in confirming the
existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this
reason there have been many efforts to associate the contributions of such
incommensurate fluctuations to the mechanism of its superconductivity. Our
unpolarized inelastic neutron scattering measurements revealed that these
incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic
factor \chi''_{c}/\chi''_{a,b} of \sim 2.8. This result is consistent with some
theoretical ideas that the incommensurate spin fluctuations with a c-axis
anisotropy can be a origin of p-wave superconductivity of this material.Comment: 5 pages, 3 figures; accepted for publication in PR
Magnetic Phase Diagram of Ca2-xSrxRuO4 Governed by Structural Distortions
We constructed, by the first-principles calculations, a magnetic phase
diagram of SrRuO in the space spanned by structural distortions. Our
phase diagram can qualitatively explain the experimental one for
CaSrRuO. We found that the rotation and the tilting of RuO
octahedron are responsible for the ferro- and antiferro-magnetism,
respectively, while the flattening of RuO is the key factor to stabilize
those magnetic ground states. Our results imply that the magnetic and the
structural instabilities in SrRuO are closely correlated cooperatively
rather than competitively.Comment: 3 figures; accepted by PRB as rapid communicatio
Linear Field Dependence of the Normal-State In-Plane Magnetoresistance of Sr2RuO4
The transverse and longitudinal in-plane magnetoresistances in the normal
state of superconducting Sr2RuO4 single crystals have been measured. At low
temperatures, both of them were found to be positive with a linear
magnetic-field dependence above a threshold field, a result not expected from
electronic band theory. We argue that such behavior is a manifestation of a
novel coherent state characterized by a spin pseudo gap in the quasi-particle
excitation spectrum in Sr2RuO4.Comment: 4 pages + 5 figure
Impurities and orbital dependent superconductivity in Sr_2RuO_4
There now exists a wealth of experimental evidence that Sr_2RuO_4 is an
odd-parity superconductor. Experiments further indicate that among the bands
stemming from the Ru {xy,xz,yz} orbitals, the portion of the Fermi surface
arising from the xy orbitals exhibits a much larger gap than the portions of
the Fermi surface arising from the {xz,yz} orbitals. In this paper the role of
impurities on such an orbital dependent superconducting state is examined
within the Born approximation. In contrast to expected results for a nodeless
p-wave superconductor the unique nature of the superconducting state in
Sr_2RuO_4 implies that a low concentration of impurities strongly influences
the low temperature behavior.Comment: 5 pages 3 figure
Detailed study of the ac susceptibility of Sr2RuO4 in oriented magnetic fields
We have investigated the ac susceptibility of the spin triplet superconductor
SrRuO as a function of magnetic field in various directions at
temperatures down to 60 mK. We have focused on the in-plane field configuration
(polar angle ), which is a prerequisite for inducing
multiple superconducting phases in SrRuO. We have found that the
previous attribution of a pronounced feature in the ac susceptibility to the
second superconducting transition itself is not in accord with recent
measurements of the thermal conductivity or of the specific heat. We propose
that the pronounced feature is a consequence of additional involvement of
vortex pinning originating from the second superconducting transition.Comment: Accepted for publication in Phys. Rev.
Low temperature electronic properties of Sr_2RuO_4 III: Magnetic fields
Based on the microscopic model introduced previously the observed specific
heat and ac-susceptibility data in the superconducting phase in Sr_2RuO_4 with
applied magnetic fields are described consistently within a phenomenological
approach. Discussed in detail are the temperature dependence of the upper
critical fields H_{c2} and H_2, the dependence of the upper critical fields on
the field direction, the linear specific heat below the superconducting phase
transition as a function of field or temperature, the anisotropy of the two
spatial components of the order parameter, and the fluctuation field H_p.Comment: 8 pages REVTEX, 4 figure
Experiential contributions to social dominance in a rat model of Fragile-X syndrome
Social withdrawal is one phenotypic feature of the monogenic neurodevelopmental disorder Fragile-X. Using a âknock-outâ rat model of Fragile-X, we examined whether deletion of the Fmr1 gene that causes this condition would affect the ability to form and express a social hierarchy as measured in a tube-test. Male Fragile-X âknock-outâ rats living together could successfully form a social dominance hierarchy, but were significantly subordinate to wild-type animals in mixed group cages. Over 10 days of repeated testing, the Fragile-X mutant rats gradually showed greater variance and instability of rank during their tube-test encounters. This affected the outcome of future encounters with stranger animals from other cages, with the initial phenotype of wild-type dominance lost to a more complex picture that reflected, regardless of genotype, the prior experience of winning or losing. Our findings offer a novel insight into the complex dynamics of social interactions between laboratory living groups of Fragile X and wild-type rats. Even though this is a monogenic condition, experience has an impact upon future interactions with other animals. Gene/environment interactions should therefore be considered in the development of therapeutics
Spin glass overlap barriers in three and four dimensions
For the Edwards-Anderson Ising spin-glass model in three and four dimensions
(3d and 4d) we have performed high statistics Monte Carlo calculations of those
free-energy barriers which are visible in the probability density
of the Parisi overlap parameter . The calculations rely on the
recently introduced multi-overlap algorithm. In both dimensions, within the
limits of lattice sizes investigated, these barriers are found to be
non-self-averaging and the same is true for the autocorrelation times of our
algorithm. Further, we present evidence that barriers hidden in dominate
the canonical autocorrelation times.Comment: 20 pages, Latex, 12 Postscript figures, revised version to appear in
Phys. Rev.
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