Flux noise in high-temperature superconductors

Spontaneously created vortex-antivortex pairs are the predominant source of flux noise in high-temperature superconductors. In principle, flux noise measurements allow to check theoretical predictions for both the distribution of vortex-pair sizes and for the vortex diffusivity. In this paper the flux-noise power spectrum is calculated for the highly anisotropic high-temperature superconductor Bi-2212, both for bulk crystals and for ultra-thin films. The spectrum is basically given by the Fourier transform of the temporal magnetic-field correlation function. We start from a Berezinskii-Kosterlitz-Thouless type theory and incorporate vortex diffusion, intra-pair vortex interaction, and annihilation of pairs by means of a Fokker-Planck equation to determine the noise spectrum below and above the superconducting transition temperature. We find white noise at low frequencies omega and a spectrum proportional to 1/omega^(3/2) at high frequencies. The cross-over frequency between these regimes strongly depends on temperature. The results are compared with earlier results of computer simulations.Comment: 9 pages, 4 PostScript figures, to be published in Phys. Rev.

NMR and NQR Fluctuation Effects in Layered Superconductors

We study the effect of thermal fluctuations of the s-wave order parameter of a quasi two dimensional superconductor on the nuclear spin relaxation rate near the transition temperature Tc. We consider both the effects of the amplitude fluctuations and the Berezinskii-Kosterlitz-Thouless (BKT) phase fluctuations in weakly coupled layered superconductors. In the treatment of the amplitude fluctuations we employ the Gaussian approximation and evaluate the longitudinal relaxation rate 1/T1 for a clean s-wave superconductor, with and without pair breaking effects, using the static pair fluctuation propagator D. The increase in 1/T1 due to pair breaking in D is overcompensated by the decrease arising from the single particle Green's functions. The result is a strong effect on 1/T1 for even a small amount of pair breaking. The phase fluctuations are described in terms of dynamical BKT excitations in the form of pancake vortex-antivortex (VA) pairs. We calculate the effect of the magnetic field fluctuations caused by the translational motion of VA excitations on 1/T1 and on the transverse relaxation rate 1/T2 on both sides of the BKT transitation temperature T(BKT)<Tc. The results for the NQR relaxation rates depend strongly on the diffusion constant that governs the motion of free and bound vortices as well as the annihilation of VA pairs. We discuss the relaxation rates for real multilayer systems where the diffusion constant can be small and thus increase the lifetime of a VA pair, leading to an enhancement of the rates. We also discuss in some detail the experimental feasibility of observing the effects of amplitude fluctuations in layered s-wave superconductors such as the dichalcogenides and the effects of phase fluctuations in s- or d-wave superconductors such as the layered cuprates.Comment: 38 pages, 12 figure

The utility of nuclear introns for investigating hybridization and genetic introgression: a case study involving Brachyramphus murrelets

Interspecific hybridization can have importantconsequences for conservation, but can bedifficult to detect using morphologicalmarkers. To test the utility of nuclear intronsfor investigating hybridization and geneticintrogression, we analyzed variation in fivenuclear introns and the mitochondrialcytochrome b gene in two species ofseabirds that are declining and may behybridizing: marbled murrelets(Brachyramphus marmoratus) and Kittlitz'smurrelets (B. brevirostris). No alleleswere shared between samples of the two species,and intron alleles formed reciprocallymonophyletic groups in gene trees. Our resultssuggest that few murrelets in Alaska areF 1, F 2or back-cross hybrids,and that gene pools of these species have beenindependent for 1.8 to 5.7 million years. Weconclude that introns are a potentially richsource of markers for analyzing hybridizationand introgression in endangered or decliningspecies

Polymerase chain reaction (PCR) primers for the amplification of five nuclear introns in vertebrates

[Extract] Advancements in evolutionary genetics, as well as the conservation of biodiversity, increasingly require direct analyses of sequence variation in nuclear DNA. Recent studies indicate that nuclear introns have variabilities useful for both phylogenetics and population genetics (reviewed in Friesen 2000); however, use of introns is currently limited by the paucity of polymerase chain reaction (PCR) primers that have been demonstrated to have broad taxonomic utility (although several primers with less general or uncertain utilities have been published; reviewed in Friesen 2000). We have designed 30 general PCR primers for nuclear introns for vertebrates

Intron variation in marbled murrelets detected using analyses of single-stranded conformational polymorphisms

Combination of the targeted amplification of nuclear introns and the analysis of single-stranded conformational polymorphisms has the potential to provide an inexpensive, rapid, versatile and sensitive genetic assay for evolutionary studies and conservation. We are developing primers and protocols to analyse nuclear introns in vertebrates, and are testing them in a population genetic study of marbled murrelets Brachyramphus marmoratus. Here we present protocols and results for introns for aldolase B, α-enolase, glyceraldehyde-3-phosphate dehydrogenase and lamin A. Results suggest that this approach presents a potentially powerful method for detecting genetic variation within and among local populations and species of animals: (i) a variety of genes can be surveyed, including genes of special interest such as those involved in disease resistance; (ii) assays are rapid and relatively inexpensive; (iii) large numbers of genes can be assayed, enabling accurate estimation of variation in the total genome; (iv) almost any mutation can be detected in the genes amplified; (v) the exact nature of variation can be investigated by sequence analysis if desired; (vi) statistical methods previously developed for proteins and/or sequence data can be used; (vii) protocols can be easily transferred to other species and other laboratories; and (viii) assays can be performed on old or degraded samples, blood or museum skins, so that animals need not be killed. Results of analyses for murrelets support earlier evidence that North American and Asiatic subspecies represent reproductively isolated species, and that genetic differences exist among murrelets from different sites within North America

Population genetic structure and conservation of marbled murrelets (Brachyramphus marmoratus)

Marbled murrelets (Brachyramphus marmoratus) are coastal seabirds that nest from California to the Aleutian Islands. They are declining and considered threatened in several regions. We compared variation in the mitochondrial control region, four nuclear introns and three microsatellite loci among194 murrelets from throughout their range except Washington and Oregon. Significant population genetic structure was found: nine private control region haplotypes and three private intron alleles occurred at high frequency in the Aleutians and California; global estimates of FST or ΦST and most pairwise estimates involving the Aleutians and/or California were significant; and marked isolation-by-distance was found. Given the available samples, murrelets appear to comprise five genetic management units: (1) western Aleutian Islands, (2) central Aleutian Islands, (3) mainland Alaska and British Columbia, (4) northern California, and (5) central California