The study on the superconductive properties of the Pr-based cuprates with quasi-one-dimensional CuO double chains

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The purpose of the present study is to clarify the superconductive properties of the Pr_2Ba_4Cu_7O_<15-δ> (Pr247) oxide superconductor with the quasi-one-dimensional CuO double chains. A high pressure apparatus is very important for this research, Therefore, another purpose of this study is do develop the 10 GPa-class high pressure cell by means of a modified Bridgman anvil method.A Pr247 oxide have been synthesized successfully, and showed superconductivity (SC) with T_c= 15 K after reduction treatment, in spite of the "Pr-issue". Reduction treatment on Pr247 caused the carrier density change by controlling the amount of oxygen deficiency in the CuO single chains. The T_c depends on the oxygen deficiency δ which is estimated from the weight change during the vacuum annealing. This indicates that the SC in the Pr247 emerges as a result of oxygen loss, i.e., electron doping, unlike in hole-based oxide superconductors. Additionally, the NQR experiment revealed that the SC is realized at … More the CuO double chains. We studied the one-dimensional conduction mechanism based on Tomonaga-Luttinger liquid theory. The CuO double chain on Pr247 can be treated as a one-dimensional (ID) structure and their results explained well the experimental results on Pr247.The pressure effects on the SC of the Pr247 have been investigated up to 10 GPa. The high pressure was produced by a newly modified Bridgman anvil type pressure cell which has been developed in the present work. The new pressure cell can produce high pressure up to 10 GPa with the expanded sample space with i.d. φ 1.5 mm, in which the resistivity for two samples can be measured at the same time. The pressure was calibrated by the structural transformation pressure of Bi, Te and Sn detected by resistivity change. The calibration at low temperature was derived from the AC susceptibility measurements on the pressure effects on the superconducting temperature of Pb. These calibration data suggested that the clamped cell holds a pressure at room temperature even in the low temperature below 10 K. The electrical resistivity on the Pr_2Ba_4Cu_7O_<15δ> with δ = 0.26, 0.68 and 0.79 was measured under the pressure with the Bridgman anvil type cell. The results are reviewed as follows;(1) High pressure suppresses the SC on the Pr247.(2) With increasing 6, the pressure required to suppress the SC is also increased.(3) After the SC vanished, the increased pressure introduces the semiconductor-like behavior of the resistivity at low temperature. Less