Superoxygenated La2-xSrxCuO4+y (LSCO+O) - Virtual and physical experiments – Niels Bohr Institute - University of Copenhagen

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Niels Bohr Institute > Calendar > 2009 > Superoxygenated La2-xS...

Superoxygenated La2-xSrxCuO4+y (LSCO+O) - Virtual and physical experiments

Superoxygenated La2-xSrxCuO4+y (LSCO+O) - virtual and physical experiments

Even though high-temperature (Tc >30 K) superconductivity was discovered in 1986, much still remains to be understood of the intricate interplay between superconducting and magnetic states within these ceramic materials. The parent compounds are anti-ferromagnetic insulators also at low temperatures. When doped by holes (to become e.g. LSCO+O), incommensurate magnetic states are formed. However superconducting states are also formed by hole-doping, and at certain doping degrees incommensurate magnetism and superconductivity coexist at low temperatures.

The present thesis investigates the crystal-structure and magnetic ordering of LSCO+O by neutron scattering. This particular system is chosen since it acts as a model system of high-temperature superconducting cuprates in the respect that the superconducting and magnetic transition temperature coincides at Tc=40 K which is the highest Tc for the LSCO compounds. Special focus is placed on investigating the neutron scattering peak shapes and widths in order to deconvolute information about the domain sizes of the different superstructures. In order to perform the deconvolution, precise information about the instrumental resolution is needed and this is provided by virtual experiments. The virtual experiments involve building a detailed replica of the neutron scattering triple axis spectrometer RITA-II within the neutron ray-traycing simulation package McStas (\verb+http://www.mcstas.org+).

In this public defense I will make an introduction to scattering and superstructures. I will also show how the detailed virtual replica of the neutron spectrometer was built and fine-tuned against physical experiments, and finally used to decovolute domain sizes of superstructures in LSCO+O by virtual experiments.