Natural linewidth analysis of d-band photoemission from Ag(110)

We report a high-resolution angle-resolved study of photoemission linewidths observed for Ag(110). A careful data analysis yields k$-resolved upper limits for the inverse inelastic lifetimes of$d$-holes at the X-point of the bulk band structure. At the upper$d$-band edge the hole-lifetime is$\tau_h \geq 22 $fs, i.e. more than one order of magnitude larger than predicted for a free-electron gas. Following calculations for$d$-hole dynamics in Cu (I.\ Campillo et al., Phys. Rev. Lett., in press) we interpret the lifetime enhancement by a small scattering cross-section of $d$- and $sp$-states below the Fermi level. With increasing distance to $E_F$ the $d$-hole lifetimes get shorter because of the rapidly increasing density of d-states and contributions of intra-$d$-band scattering processes, but remain clearly above free-electron-model predictions.Comment: 14 pages, 7 figure

Systematic X-ray absorption study of hole doping in BSCCO - phases

X-ray absorption spectroscopy (XAS) on the O 1s threshold was applied to Bi-based, single crystalline high temperature superconductors (HTc's), whose hole densities in the CuO2 planes was varied by different methods. XAS gives the intensity of the so-called pre-peak of the O 1s line due to the unoccupied part of the Zhang-Rice (ZR) singlet state. The effects of variation of the number n of CuO2 - planes per unit cell (n = 1,2,3) and the effect of La-substitution for Sr for the n = 1 and n = 2 phase were studied systematically. Furthermore the symmetry of the states could be probed by the polarization of the impinging radiation.Comment: 4 pages, 2 figures, to appear in the proceedings of SCES2001, Ann Arbor, August 6-10, 200

Aggregation Behavior And Chromonic Liquid Crystal Properties Of An Anionic Monoazo Dye

X-ray scattering and various optical techniques are utilized to study the aggregation process and chromonic liquid crystal phase of the anionic monoazo dye Sunset Yellow FCF. The x-ray results demonstrate that aggregation involves pi-pi stacking of the molecules into columns, with the columns undergoing a phase transition to an orientationally ordered chromonic liquid crystal phase at high dye concentration. Optical absorption measurements on dilute solutions reveal that the aggregation takes place at all concentrations, with the average aggregation number increasing with concentration. A simple theory based on the law of mass action and an isodesmic aggregation process is in excellent agreement with the experimental data and yields a value for the bond energy between molecules in an aggregate. Measurements of the birefringence and order parameter are also performed as a function of temperature in the chromonic liquid crystal phase. The agreement between these results and a more complicated theory of aggregation is quite reasonable. Overall, these results both confirm that the aggregation process for some dyes is isodesmic and provide a second example of a well-characterized chromonic system

Quasiparticles and Energy Scaling in Bi2_2Sr2_2Can−1_{n-1}Cun_nO2n+4_{2n+4} (n\it{n}=1-3): Angle-Resolved Photoemission Spectroscopy

Angle-resolved photoemission spectroscopy (ARPES) has been performed on the single- to triple-layered Bi-family high-{\it T$_c$} superconductors (Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4}$, $\it{n}$=1-3). We found a sharp quasiparticle peak as well as a pseudogap at the Fermi level in the triple-layered compound. Comparison among three compounds has revealed a universal rule that the characteristic energies of superconducting and pseudogap behaviors are scaled with the maximum {\it T$_c$}.Comment: 4 pages, 4 figure

Unusual electronic ground state of a prototype cuprate: band splitting of single CuO_2-plane Bi_2 Sr_(2-x) La_x CuO_(6+delta)

By in-situ change of polarization a small splitting of the Zhang-Rice singlet state band near the Fermi level has been resolved for optimum doped (x=0.4) Bi$_{2}$Sr$_{2-x}$La$_{x}$CuO$_{6+\delta}$ at the (pi,0)-point (R.Manzke et al. PRB 63, R100504 (2001). Here we treat the momentum dependence and lineshape of the split band by photoemission in the EDC-mode with very high angular and energy resolution. The splitting into two destinct emissions could also be observed over a large portion of the major symmetry line $\Gamma$M, giving the dispersion for the individual contributions. Since bi-layer effects can not be present in this single-layer material the results have to be discussed in the context of one-particle removal spectral functions derived from current theoretical models. The most prominent are microscopic phase separation including striped phase formation, coexisting antiferromagnetic and incommensurate charge-density-wave critical fluctuations coupled to electrons (hot spots) or even spin charge separation within the Luttinger liquid picture, all leading to non-Fermi liquid like behavior in the normal state and having severe consequences on the way the superconducting state forms. Especially the possibilty of observing spinon and holon excitations is discussed.Comment: 5 pages, 4 figure

Sequencing and characterization of the guppy (Poecilia reticulata) transcriptome

Background: Next-generation sequencing is providing researchers with a relatively fast and affordable option for developing genomic resources for organisms that are not among the traditional genetic models. Here we present a de novo assembly of the guppy (Poecilia reticulata) transcriptome using 454 sequence reads, and we evaluate potential uses of this transcriptome, including detection of sex-specific transcripts and deployment as a reference for gene expression analysis in guppies and a related species. Guppies have been model organisms in ecology, evolutionary biology, and animal behaviour for over 100 years. An annotated transcriptome and other genomic tools will facilitate understanding the genetic and molecular bases of adaptation and variation in a vertebrate species with a uniquely well known natural history. Results: We generated approximately 336 Mbp of mRNA sequence data from male brain, male body, female brain, and female body. The resulting 1,162,670 reads assembled into 54,921 contigs, creating a reference transcriptome for the guppy with an average read depth of 28×. We annotated nearly 40% of this reference transcriptome by searching protein and gene ontology databases. Using this annotated transcriptome database, we identified candidate genes of interest to the guppy research community, putative single nucleotide polymorphisms (SNPs), and male-specific expressed genes. We also showed that our reference transcriptome can be used for RNA- sequencing-based analysis of differential gene expression. We identified transcripts that, in juveniles, are regulated differently in the presence and absence of an important predator, Rivulus hartii, including two genes implicated in stress response. For each sample in the RNA-seq study, >50% of high-quality reads mapped to unique sequences in the reference database with high confidence. In addition, we evaluated the use of the guppy reference transcriptome for gene expression analyses in a congeneric species, the sailfin molly (Poecilia latipinna). Over 40% of reads from the sailfin molly sample aligned to the guppy transcriptome. Conclusions: We show that next-generation sequencing provided a reliable and broad reference transcriptome. This resource allowed us to identify candidate gene variants, SNPs in coding regions, and sex-specific gene expression, and permitted quantitative analysis of differential gene expression