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arXiv · 1604.04056

Multiple Antiferromagnetic Spin Fluctuations and Novel Evolution of Tc in Iron-based superconductors LaFe(As1-xPx)(O1-yFy) revealed by 31P-NMR Studies

T. Shiota·H. Mukuda·M. Uekubo·F. Engetsu·M. Yashima·Y. Kitaoka·K. T. Lai·H. Usui·K. Kuroki·S. Miyasaka·S. Tajima
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Abstract

We report on 31P-NMR studies of LaFe(As_{1-x}P_x)(O_{1-y}F_{y}) over wide compositions for 0<x<1 and 0<y<0.14, which provide clear evidence that antiferromagnetic spin fluctuations (AFMSFs) are one of the indispensable elements for enhancing Tc. Systematic 31P-NMR measurements revealed two types of AFMSFs in the temperature evolution, that is, one is the AFMSFs that develop rapidly down to Tc with low-energy characteristics, and the other, with relatively higher energy than the former, develops gradually upon cooling from high temperature. The low-energy AFMSFs in low y (electron doping) over a wide x (pnictogen height suppression) range are associated with the two orbitals of d_{xz/yz}, whereas the higher-energy ones for a wide y region around low x originate from the three orbitals of d_{xy} and d_{xz/yz}. We remark that the nonmonotonic variation of Tc as a function of x and y in LaFe(As_{1-x}P_x)(O_{1-y}F_y) is attributed to these multiple AFMSFs originating from degenerated multiple 3d orbitals inherent to Fe-pnictide superconductors.

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T. Shiota, H. Mukuda, M. Uekubo, F. Engetsu, M. Yashima, Y. Kitaoka, K. T. Lai, H. Usui, K. Kuroki, S. Miyasaka, S. Tajima. 2016-04-14. Multiple Antiferromagnetic Spin Fluctuations and Novel Evolution of Tc in Iron-based superconductors LaFe(As1-xPx)(O1-yFy) revealed by 31P-NMR Studies. https://doi.org/10.7566/jpsj.85.053706

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