MICROSCOPIC ANNEALING PROCESS AND ITS IMPACT ON SUPERCONDUCTIVITY IN T'-STRUCTURE ELECTRON DOPED CUPRATES
H. J. Kang, P. Dai, B. J. Campbell, P. J. Chupas, S. Rosenkranz, P. L. Lee, Q. Huang, S. Li, S. Komiya, and Y. Ando
High-transition-temperature superconductivity arises in copper oxides when holes or electrons are doped into their antiferromagnetic (AF) insulating parent compounds. For hole-doped copper oxide materials, hole doping quickly destroys the AF order and induces superconductivity. However, in electron-doped copper oxide materials, electron doping alone is not sufficient to induce superconductivity. Superconductivity is only achieved only when the doped as-grown samples are annealed in an oxygen reduced atmosphere to remove a small amount of oxygen. The role of the reduction process in the superconductivity of electron-doped high-Tc copper oxides has been a long-standing unsolved problem.
Previous work suggests that oxygen reduction may influence mobile carrier concentrations, decrease disorder/impurity scattering, or suppress the long-range AF order. However, the microscopic process of oxygen reduction and its effect on superconductivity is still unknown.
Our x-ray and neutron scattering data, combined with chemical and thermo-gravimetric analysis measurements in the electron-doped Pr0.88LaCe0.12CuO4 show that the microscopic process of oxygen reduction removes Cu deficiencies in the as-grown materials and creates oxygen vacancies in the stoichiometric CuO2 plane. Our results thus indicate that the role of annealing is to repair disorder in the CuO2 plane induced by Cu deficiencies and to provide itinerant carriers for superconductivity. This suggests that the fundamental mechanism for superconductivity is the same for electron- and hole-doped copper oxides.
Presenter: Hye Jung Kang
Mentor: Jeffrey Lynn
Laboratory: NIST Center for Neutron Research
Neutron Condensed Matter Science
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