C-axis lattice dynamics in Bi-based cuprate superconductors

We present results of a systematic study of the c axis lattice dynamics in single layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212) and trilayer Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate superconductors. Our study is based on both experimental data obtained by spectral ellipsometry on single crystals and theoretical calculations. The calculations are carried out within the framework of a classical shell model, which includes long-range Coulomb interactions and short-range interactions of the Buckingham form in a system of polarizable ions. Using the same set of the shell model parameters for Bi2201, Bi2212 and Bi2223, we calculate the frequencies of the Brillouin-zone center phonon modes of A2u symmetry and suggest the phonon mode eigenvector patterns. We achieve good agreement between the calculated A2u eigenfrequencies and the experimental values of the c axis TO phonon frequencies which allows us to make a reliable phonon mode assignment for all three Bi-based cuprate superconductors. We also present the results of our shell model calculations for the Gamma-point A1g symmetry modes in Bi2201, Bi2212 and Bi2223 and suggest an assignment that is based on the published experimental Raman spectra. The superconductivity-induced phonon anomalies recently observed in the c axis infrared and resonant Raman scattering spectra in trilayer Bi2223 are consistently explained with the suggested assignment.Comment: 29 pages, 13 figure

Von der Kultur zum Kommerz: EU-Politik für staatliche Beihilfen und öffentlich-rechtlicher Rundfunk

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Consulting pupils in assessment for learning classrooms: the twists and turns of working with students as co‐researchers

Research literature on students as researchers demonstrates a spectrum of constructive ways in which students are being actively engaged in school and classroom action inquiries. Any identified tensions lie in the degree to which students themselves are genuinely engaged as action researchers. Increasingly, externally driven agendas for change and improvement are appropriating action research as means to facilitate teachers in developing new skills and tailor‐making national initiatives. According students appropriately democratic roles in such research processes are a lot less evident. This paper illustrates and discusses some of the difficulties, tensions and positive outcomes of engaging with students as co‐researchers at Key Stage 3 within a nationally funded project that intersects an action research policy framework supporting the introduction of Assessment for Learning throughout Northern Ireland. Issues discussed include student research advisory groups, students as data gatherers and students acting as co‐interpreters of video‐taped and image‐based classroom data