Scanning tunneling microscopy/spectroscopy on multi-layered cuprate superconductor Ba2Ca5Cu6O12 (O1−x Fx)2 |
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Authors: | A Sugimoto K Shohara T Ekino Y Watanabe Y Harada S Mikusu K Tokiwa T Watanabe |
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Institution: | aGraduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan;bDepartment of Applied Electronics, Tokyo University of Science, Chiba 278-8510, Japan |
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Abstract: | Scanning tunneling microscopy/spectroscopy (STM/STS) measurements on multi-layered cuprate superconductor Ba2Ca5Cu6O12 (O1−x Fx)2 are carried out. STM topographies show randomly distributed bright spot structures with a typical spot size of 0.8 nm. These bright spots are occupied about 28% per one unit cell of c-plane, which is comparable to the regular amount of apical oxygen of 20% obtained from element analysis. Tunneling spectra simultaneously show both the small and the large gap structures. These gap sizes at 4.9 K are about Δ 15 meV and 90 meV, respectively. The small gap structure disappears at the temperature close to TC, while the large gap persists up to 200 K. Therefore, these features correspond to the superconducting gap and pseudogap, respectively. These facts give evidence for some ordered state with large energy scale even in the superconducting state. For the superconducting gap, the ratio of 2Δ/KBTC = 4.9 is obtained with TC = 70 K, which is determined from temperature dependence of the tunneling spectra. |
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Keywords: | Ba2Ca5Cu6O12 (O1− x Fx)2 F0256 STM Tunneling spectroscopy |
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