Heat Treatment Effects on the Superconductivity and Crystal Structure of Nd_<1.85>Ce_<0.15>CuO_4 Studied Using a Single Crystal

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We performed systematic post-growth heat treatments on sizable single crystals of Nd<1.85>Ce_<0.15>CuO_4. The superconducting transition temperature, T_c, and its distribution in the sample are both sensitive to details of the heat treatment and sample size. With refinement of the heat treatment conditions we have succeeded in preparing two distinct superconducting samples in which T_c equals 18K and 25K under identical Ce-concentrations. Neutron scattering experiments initially observed nonmagnetic super-structure peaks at (π,π) only in the reduced superconducting phase. Atomic displacement in this structure is different from that induced by in-plane rotation of CuO_4 squares as previously reported for Gd_<2-x>Ce_xCuO_4. A possible relationship between atomic displacements and superconductivity and the role of reduced heat treatments are discussed from the viewpoint of carrier localization.
社団法人日本物理学会の論文
2002-03-15