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- 저자 : Akira Iyo (검색결과 2 건)
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Superconducting Properties of Ba2Ca7Cu8O16(O0.8+δF1.2) Studied via Reversible Magnetization
권용태,김영철,김헌정,Akira Iyo,Parasharam M. Shirage 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.11
The Ba<sub>2</sub>Ca<sub>7</sub>Cu<sub>8</sub>O<sub>16</sub>(O<sub>0.8+δ</sub>F<sub>1.2</sub>) (F-0278) superconductor with 8 CuO<sub>2</sub> planes in the structural unit was investigated by analyzing the reversible magnetization based on the Hao-Clem model and fluctuation theories. In spite of the superconducting block (SCB) being thicker than the charge reservoir block (CRB), the analysis clearly revealed two-dimensional (2D) superconducting properties in F-0278, such as a strong temperature dependence of the Ginzburg parameter κ and a relatively short effective interlayer distance. The extreme 2D behavior can be understood in terms of the significant charge imbalance in the SCB, which was previously proposed to exist in F-0278, where the carriers are distributed quite unequally to crystallographically different CuO2 planes; <i>i.e.</i>, the outer planes (OPs) adjacent to the CRB always contain more carriers than the inner planes (IPs). The 2D nature of F-0278 indicates a significant or complete suppression of the superconductivity in the IPs. The important superconducting parameters were also obtained from the analysis.
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Takayoshi Kouchi,Kyohei Yoshinaga,Tomoya Asano,Mitsuharu Yashima,Hidekazu Mukuda,Sotaro Nishioka,Tsuyoshi Kawashima,Shigeki Miyasaka,Akira Iyo 한국물리학회 2023 새물리 Vol.73 No.12
We performed isotope <SUP>121,123</SUP>Sb-NMR studies to investigate the role of nematic fluctuations for superconductivity in Sb-substituted iron-based compounds LaFe(As<SUB>1-x</SUB>Sb<SUB>x</SUB>)O<SUB>1-y</SUB>F<SUB>y</SUB>. The temperature(T) dependence of nuclear spin relaxation rate(1=T₁) of <SUP>121,123</SUP>Sb were measured in the parent compound LaFe(As<SUB>0.6</SUB>Sb<SUB>0.4</SUB>)O(F0Sb40) and the lightly electron doped LaFe(As<SUB>0.7</SUB>Sb<SUB>0.3</SUB>)O<SUB>0.9</SUB>F<SUB>0.1</SUB>(F10Sb30). In the F0Sb40, the <SUP>121,123</SUP>(1=T₁) were enhanced upon cooling toward structural transition temperature (T<SUB>s</SUB> ~ 135 K) and show a peak at T<SUB>s</SUB>. The isotopic ratio (<SUP>123</SUP>T₁<SUP>-1</SUP> /<SUP>121</SUP>T₁<SUP>-1</SUP> ) reveals that the electric quadrupole relaxation originated from the dynamics of electric field gradient at Sb site is enhanced toward Ts. It is due to the presence of critically enhanced nematic fluctuations of the stripe-type order of Fe-3d<SUB>xz</SUB> (or 3d<SUB>yz</SUB>) orbitals. In the F10Sb30(T<SUB>c</SUB> ~ 20 K), the nematic fluctuations were significantly suppressed, but it remains a small enhancement below 80 K while keeping the C₄ symmetry. These results suggested that the orbital degrees of freedom remain even in the tetragonal structure of the lightly electron doped superconducting phase (SC1) of La1111 compounds. Here, we discuss the contribution of nematic fluctuations in Fe-pnictide superconductivity by mean of the electric quadrupole moment of isotope <SUP>121,123</SUP>Sb nuclei.
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