Anomalous proximity effect in d-wave superconductors

The anomalous proximity effect between a d-wave superconductor and a surface layer with small electronic mean free path is studied theoretically in the framework of the Eilenberger equations. The angular and spatial structure of the pair potential and the quasiclassical propagators in the interface region is calculated selfconsistently. The variation of the spatially-resolved quasiparticle density of states from the bulk to the surface is studied. It is shown that the isotropic gapless superconducting state is induced in the disordered layer.Comment: 6 pages, 5 postscript figures. Submitted to Phys.Rev.

Two regimes for effects of surface disorder on the zero-bias conductance peak of tunnel junctions involving d-wave superconductors

Impurity-induced quasiparticle bound states on a pair-breaking surface of a d-wave superconductor are theoretically described, taking into account hybridization of impurity- and surface-induced Andreev states. Further a theory for effects of surface disorder (of thin impurity surface layer) on the low-bias conductance of tunnel junctions is developed. We find a threshold $n_c$ for surface impurity concentration $n_S$, which separates the two regimes for surface impurity effects on the zero-bias conductance peak (ZBCP). Below the threshold, surface impurities do not broaden the ZBCP, but effectively reduce its weight and generate impurity bands. For low $n_S$ impurity bands can be, in principle, resolved experimentally, being centered at energies of bound states induced by an isolated impurity on the surface. For larger $n_S$ impurity bands are distorted, move to lower energies and, beginning with the threshold concentration $n_S=n_c$, become centered at zero energy. With increasing $n_S$ above the threshold, the ZBCP is quickly destroyed in the case of strong scatterers, while it is gradually suppressed and broaden in the presence of weak impurity potentials. More realistic cases, taking into account additional broadening, not related to the surface disorder, are also considered.Comment: 9 pages, 7 figure

Quasiparticle Bound States and Low-Temperature Peaks of the Conductance of NIS Junctions in d-Wave Superconductors

Quasiparticle states bound to the boundary of anisotropically paired superconductors, their contributions to the density of states and to the conductance of NIS junctions are studied both analytically and numerically. For smooth surfaces and real order parameter we find some general results for the bound state energies. In particular, we show that under fairly general conditions quasiparticle states with nonzero energies exist for momentum directions within a narrow region around the surface normal. The energy dispersion of the bound states always has an extremum for the direction along the normal. Along with the zero-bias anomaly due to midgap states, we find, for quasi two-dimensional materials, additional low-temperature peaks in the conductance of NIS junctions for voltages determined by the extrema of the bound state energies. The influence of interface roughness on the conductance is investigated within the framework of Ovchinnikov's model. We show that nonzero-bias peaks at low temperatures may give information on the order parameter in the bulk, even though it is suppressed at the surface.Comment: 14 pages, PostScrip

Using WormBase: A Genome Biology Resource for Caenorhabditis elegans and Related Nematodes

WormBase (www.wormbase.org) provides the nematode research community with a centralized database for information pertaining to nematode genes and genomes. As more nematode genome sequences are becoming available and as richer data sets are published, WormBase strives to maintain updated information, displays, and services to facilitate efficient access to and understanding of the knowledge generated by the published nematode genetics literature. This chapter aims to provide an explanation of how to use basic features of WormBase, new features, and some commonly used tools and data queries. Explanations of the curated data and step-by-step instructions of how to access the data via the WormBase website and available data mining tools are provided

A gene expression fingerprint of C. elegans embryonic motor neurons

BACKGROUND: Differential gene expression specifies the highly diverse cell types that constitute the nervous system. With its sequenced genome and simple, well-defined neuroanatomy, the nematode C. elegans is a useful model system in which to correlate gene expression with neuron identity. The UNC-4 transcription factor is expressed in thirteen embryonic motor neurons where it specifies axonal morphology and synaptic function. These cells can be marked with an unc-4::GFP reporter transgene. Here we describe a powerful strategy, Micro-Array Profiling of C. elegans cells (MAPCeL), and confirm that this approach provides a comprehensive gene expression profile of unc-4::GFP motor neurons in vivo. RESULTS: Fluorescence Activated Cell Sorting (FACS) was used to isolate unc-4::GFP neurons from primary cultures of C. elegans embryonic cells. Microarray experiments detected 6,217 unique transcripts of which ~1,000 are enriched in unc-4::GFP neurons relative to the average nematode embryonic cell. The reliability of these data was validated by the detection of known cell-specific transcripts and by expression in UNC-4 motor neurons of GFP reporters derived from the enriched data set. In addition to genes involved in neurotransmitter packaging and release, the microarray data include transcripts for receptors to a remarkably wide variety of signaling molecules. The added presence of a robust array of G-protein pathway components is indicative of complex and highly integrated mechanisms for modulating motor neuron activity. Over half of the enriched genes (537) have human homologs, a finding that could reflect substantial overlap with the gene expression repertoire of mammalian motor neurons. CONCLUSION: We have described a microarray-based method, MAPCeL, for profiling gene expression in specific C. elegans motor neurons and provide evidence that this approach can reveal candidate genes for key roles in the differentiation and function of these cells. These methods can now be applied to generate a gene expression map of the C. elegans nervous system

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field

Synthese und Supraleitung von Molybdän Clusterverbindungen (Chevrel-Phasen)

The discovery of superconductivity in ternary molybdenum sulfides (Chevrel phases) in 1972 has stimulated research on these compounds. Some of these phases show extremely high critical fields H$_{c2}$ and might therefore find technical application as high field superconductors. In order to understand the electron-phonon-interaction in these substances, measurements of the superconducting isotope effect in $^{92-100}Mo_{6}Se_{8}$ , $Mo_{6}$$^{76-82}Se_{8}$ , and $^{116-124}SnMo_{6}S_{8}$ have been performed. The corresponding isotope effect exponents$\beta$ ($\beta_{Mo}$=0.27 $\pm$ 0.04 , $\beta_{Se}$=0.27 $\pm$ 0.05 and $\vert \beta_{Sn} \vert \le 0.05)$ have been calculated by fitting the experimental data to the relation $T_{c}M^{\beta}$=const. We have shown that phonon modes connected with Se-displacements as weIl as modes connected with Mo-displacements couple to the conduction electron system in $Mo_{6}Se_{8}$. In case of the ternary Chevrel phase SnMo$_{6}$S$_{8}$, phonon modes connected with displacements of the Sn-ions have only minor influence on the transition temperature. This result can be explainedby the weak overlap of the molybdenum $d_{x}2_{-y}2$ - orbitals with Sn-sites. Furthermore I we report experiments on the synthesis of new Chevrel phase material . In order to optimize the valence electron concentration in some ternary molybdenum selenide compounds I chalcogen exchange reactions have been performed. A new Chevrel phase superconductor , $Cu_{x}Mo_{6}S_{6}J_{2}$ with x=0 - 1.2 , has been synthesized by copper diffusion into the non occupied channels running between the $Mo_{6}S_{6}J_{2}$-"molecules" of $Mo_{6}S_{6}J_{2}$

Theory of the isotope effect in superconducting compounds

We present a theoretical analysis of the isotope effect on the superconducting transition temperature. Our method is to calculate via formal perturbation theory the response of the transition temperature to small changes of the masses of the various constituents of the compound. We discuss the relation between the isotope effect and various more fundamental parameters in strong coupling superconductors, such as $\mu$* and $\alpha$2 F($\omega$). As illustrative examples, we consider the systems Pd-H(D) alloys and the binary Chevrel phase superconductor Mo$_{6}$Se$_{8}$, and show that analysis of the isotope effect can yield useful information concerning interaction mechanisms in these compounds

Discovery of native aluminum on Variscan metagranitoids in Upper Carinthia, Austria: natural or anthropogenic origin?

Native aluminum was discovered in 2004 at Hochwurten, Goldberg mountain group, Upper Carinthia, Austria. The discovery site is close to the Wurtenkees (glacier), where the dominant rock (Central gneiss) was exposed during the retreat of the glacier. Here, also veins with gold-bearing ores associated with tellurides (tetradymite, tsumoite, joséite-A) and Ag–Pb–Bi-sulfosalts are exposed and were mined intermittently during the last centuries. Native aluminum occurs at some distance (several 100 m laterally and vertically) to the veins as an isolated crystalline aggregate measuring 10 × 3 mm, and a closely associated flake (200 µm length), which was used for most of the studies. Both occur on gneiss and are intensely intergrown with it. Two groups of inclusions in the aluminum were observed and studied by SEM and EPMA. Group one consists of Bi–Te–(S)–(O) minerals, such as tetradymite, Bi2Te2S, tsumoite, BiTe, tellurobismuthite, Bi_2Te_3, bismuth and a montanite-type secondary mineral. The other group contains a new phase with composition (Al,Si)_(19)Fe_4, rare grains of hollisterite (Al_3Fe), and abundant Zn,Mg-bearing metallic nano-phases. A transition zone is developed between native aluminum and albite, a constituent of the gneiss, and is characterized by strongly changing concentrations of aluminum, silicon, iron and sulfur. Micro-computed tomography studies reveal that the Al metal is clearly intermixed with the host rock and not just juxtaposed over it. To shed further light on the origin of the Al metal, SIMS Mg isotopic measurements were carried out on the Austrian aluminum and on selected synthetic alloys with similar composition. A thorough discussion about the possible naturalness of this native aluminum and its possible formation is presented. The paper aims at augmenting the rare, assured knowledge of native metal formation/alteration under crustal and subcrustal conditions