Importance of $${{d}}_{{{xy}}}$$ orbital and electron correlation in iron-based superconductors revealed by phase diagram for 1111-system
Tsuyoshi Kawashima, S. Miyasaka, Hirokazu Tsuji, Takahiro Yamamoto, M. Uekubo, Akira Takemori, Kwing To Lai, S. Tajima
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 [Formula: see text] is strongly affected by the pnictogen height [Formula: see text] from the Fe-plane that controls the electron correlation strength and the size of the [Formula: see text] hole Fermi surface (FS). With increasing [Formula: see text], weak coupling BCS superconductivity switches to the strong coupling non-BCS one where electron correlations and the [Formula: see text] hole FS may be important.