title: High-Tc superconductivity near the anion height instability in Fe-based superconductors: analysis of LaFeAsO(1-x)H(x).
abstract: The isostructural transition in the tetragonal phase with a sizable change in the anion height, is realized in heavily H-doped LaFeAsO and (La,P) codoped CaFe2As2. In these compounds, the superconductivity with higher Tc (40-50 K) is realized near the isostructural transition. To find the origin of the anion-height instability and the role in realizing the higher-Tc state, we develop the orbital-spin fluctuation theory by including the vertex correction. We analyze LaFeAsO(1-x)H(x) and find that the non-nematic orbital fluctuations, which induce the anion-height instability, are automatically obtained at x∼0.5, in addition to the conventional nematic orbital fluctuations at x∼0. The non-nematic orbital order triggers the isostructural transition, and its fluctuation would be a key ingredient to realize higher-Tc superconductivity of order 50 K.
authors.affiliation: Department of Applied Physics, Nagoya University, Furo-cho, Nagoya 464-8603, Japan.
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Onari
authors.affiliation: Department of Physics, Nagoya University, Furo-cho, Nagoya 464-8602, Japan.
authors.forename: Youichi
authors.initials: Y
authors.lastname: Yamakawa
authors.affiliation: Department of Physics, Nagoya University, Furo-cho, Nagoya 464-8602, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kontani