Importance of $${{d}}_{{{xy}}}$$ d xy orbital and electron correlation in iron-based superconductors revealed by phase diagram for 1111-system

• Main Authors: Tsuyoshi Kawashima, Shigeki Miyasaka, Hirokazu Tsuji, Takahiro Yamamoto, Masahiro Uekubo, Akira Takemori, Kwing To Lai, Setsuko Tajima
• Format: Article
• Language: English
• Published: Nature Publishing Group 2021-05-01
• Series: Scientific Reports
• Online Access: https://doi.org/10.1038/s41598-021-89231-2

Abstract The structural flexibility at three substitution sites in LaFeAsO enabled investigation of the relation between superconductivity and structural parameters over a wide range of crystal compositions. Substitutions of Nd for La, Sb or P for As, and F or H for O were performed. All these substitutions modify the local structural parameters, while the F/H-substitution also changes band filling. It was found that the superconducting transition temperature $$T_{\text{c}}$$ T c is strongly affected by the pnictogen height $$h_{Pn}$$ h Pn from the Fe-plane that controls the electron correlation strength and the size of the $$d_{xy}$$ d xy hole Fermi surface (FS). With increasing $$h_{Pn}$$ h Pn , weak coupling BCS superconductivity switches to the strong coupling non-BCS one where electron correlations and the $$d_{xy}$$ d xy hole FS may be important.