Local Structural Properties Around Cu Atoms in Checkerboard Phased Ca2−x Na x CuO2Cl2
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We examined the local structural properties of checkerboard phased Ca2−x Na x CuO2Cl2 (T c =0, 15, 21, 27 K) using extended X-ray absorption fine structure (EXAFS) measurements at the Cu K edge. EXAFS revealed anomalous disorders existing in the bond lengths of Cu–Cu and Cu-Ca/Na pairs for all crystals below 50 K. A static disorder was observed even at room temperature. The disorders of the Cu–Cu in the a- and b-axes were independent of the T c value whereas these of the Cu–Ca/Na pairs located about 30∘ off from the Cu–O, ab-plane decreased, as T c increased.
KeywordsNaCCOC Checkerboard phase Superconductivity EXAFS Structure
The work at Chonbuk National University was supported by the Basic Science Research Program through the National Research Foundation of Korea government (NRF) grant funded by the Korean Ministry of Education, Science and Technology (MEST) (No. 2012R1A1A4A01007669). The XAFS data were collected at the 20BM beamline of APS, Argonne National Laboratory and at the 8C beamline of PLS.