Interplay between magnetism and superconductivity in high-temperature superconductors La(2−x)Ba(x)CuO(4) and Fe(1+y)Te(1−x)Se(x): crystal growth and neutron scattering studies
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In this Dissertation, I combined neutron scattering with susceptibility, and transport measurements on two types of high-temperature superconductors La<sub>2-x</sub>Ba<sub>x</sub>CuO<sub>4</sub>, and Fe<sub>1+y</sub>Te<sub>1-x</sub>Se<sub>x</sub> to study theinterplay between magnetism and superconductivity. By studyingLa<sub>2-x</sub>Ba<sub>x</sub>CuO<sub>4</sub> with crystals grown by a floating-zone technique,it is found that static magnetic order competes with superconductivity,with the observation that both magnetic field and Znimpurity reduce the superconductivity and enhance the magneticorder. By studying the doping and magnetic-field dependence onFe<sub>1+y</sub>Te<sub>1-x</sub>Se<sub>x</sub> with crystals grown by a horizontal unidirectionalsolidification method, it is revealed that magnetic fluctuations areessential for superconductivity. The results are consistent with theidea that magnetic excitations act as the"glue" to pair the electrons,and render the superconductivity.