Observation of local orbital states and their role for the electronic state

2017 Fiscal Year Final Research Report

• Project/Area Number: 15K05167
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Condensed matter physics II
• Research Institution: Nagoya University
• Principal Investigator: Kobayashi Yoshiaki 名古屋大学, 理学研究科, 准教授 (60262846)
• Co-Investigator(Kenkyū-buntansha): 伊藤 正行 名古屋大学, 理学研究科, 教授 (90176363)
• Project Period (FY): 2015-04-01 – 2018-03-31
• Keywords: ネマチック状態 / 鉄系超伝導体 / 軌道秩序 / 核磁気共鳴 / 電場勾配 / ナイトシフト / 磁気ゆらぎ / 電荷ゆらぎ

Outline of Final Research Achievements

Nematic fluctuation was investigated from 75As nuclear magnetic resonance for the iron based superconductors Ba(Fe1-xCox)2As2, NaFeAs, and LiFeAs. We found that the electric nematic fluctuation obtained from Raman scattering can be monitored from the temperature and x dependence of the in-plane anisotropy (eta) of the electric field gradient at the As nuclear position. The eta for all samples shows Curie-Weiss type temperature dependence, where the fitting parameters, C_eta and T_eta, which correspond to Curie constant and the Weiss temperatures, respectively, systematically have x-dependences. The T_eta’s show roughly ~ Ts-50 (K) in x <0.05 where the nematic order emerges (Ts is nematic ordered temperature). Similarly with the result of Raman scattering, the T_eta becomes zero with x~0.055. At x>0.055, we found that the T_eta’s become negative, suggesting the existence of antiferro-type orbital fluctuation.

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