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

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

Agency practically imparted: a media-didactical workshop conception

Im folgenden Artikel wird ein mehrstufiges mediendidaktisches Workshop-Konzept vorstellt. Ziel des Angebots ist die praxisnahe Vermittlung von Grundlagen anhand von Fallbeispielen. Der Workshop wurde im Rahmen des seit 2012 durch das BMBF geförderten, sächsischen Verbundprojekts Lehrpraxis im Transfer (LiT) zur Qualifizierung für den Bereich Neue Medien entwickelt. Im Artikel werden die Philosophie und Genese von «Neue Lehre durch Neue Medien? – Sinnvoller Einsatz von Neuen Medien in der Hochschullehre» dargestellt und ein Einblick in Konzeption und Durchführung der Weiterbildung gegeben. Das Konzept richtet sich an Vertreter/innen aller Fachrichtungen und vermittelt mediendidaktische und damit einhergehend hochschuldidaktische Grundlagen. Zur niedrigschwelligen Veranschaulichung der Thematik wird mit Beispielen guter Lehrpraxis gearbeitet. Das Angebot richtet sich an Lehrende, die das Sächsische Hochschuldidaktik Zertifikat erlangen wollen und ist im Zertifikatsprogramm des Hochschuldidaktischen Zentrums Sachsen (HDS) im Bereich «Neue Medien» anrechenbar. Derzeit wird «Neue Lehre durch Neue Medien?» als offene Bildungsressource aufbereitet und zur Nutzung für Weiterbildner/innen zur Verfügung gestellt.The following article introduces a multilevel media-didactical workshop conception, which was developed within the Saxonian network-project for Higher Education Lehrpraxis im Transfer. The aim is the practical teaching of basic didactics through case studies. The workshop was developed within the Saxonian network-project Lehrpraxis im Transfer (LiT) in the field of new media. The article will present the philosophy and generation of «Neue Lehre durch Neue Medien? – Sinnvoller Einsatz von Neuen Medien in der Hochschullehre» and pursue the conception and its implementation. It focuses all teachers in higher education of all subjects and introduces basics in media-didactics and Higher Education by the use of good practice. The workshop addresses teachers in Higher Education, aiming to achieve the certificate of the Hochschuldidaktisches Zentrum Sachsen – Center for Higher Education in Saxony (HDS) within the field of new media. «Neue Lehre durch Neue Medien?» is currently edited for the use as Open Educational Resource

Comparative study of the electronic structures of the In and Sn/In2O3 (111) interfaces

The electronic structure of the transparent semiconductor In2O3 has been studied by angle resolved photoemission spectroscopy upon deposition of metallic indium and also tin on the surface of the semiconductor. By deposition of metallic indium on In2O3 (111) single crystals, we detected the formation of a free-electron like band of effective mass (0.38+-0.05) m0. At low coverages, metallic In shifts the Fermi level of In2O3 to higher energies and a new electronic state forms at the metal/semiconductor interface. This state of two-dimensional character (2D-electron gas) is completely responsible for the electrical conduction in In2O3 (111) at the surface region and has a band dispersion, which does not correspond to the previously found surface accumulation layers in this material. Despite the similarity of the electronic properties of In and Sn, a larger downward banding was observed by Sn coverage, which was not accompanied by the appearance of the surface state.Comment: 5 pages, 3 figure

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

Scopes and Limits of Modality in Quantum Mechanics

We develop an algebraic frame for the simultaneous treatment of actual and possible properties of quantum systems. We show that, in spite of the fact that the language is enriched with the addition of a modal operator to the orthomodular structure, contextuality remains a central feature of quantum systems.Comment: 9 pages, no figure

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