title: Comprehensive studies for the crystal structures and electronic properties of the superconducting system Fe(1 + δ)Se(1 - x)Te(x) with δ is approximately equal to 0.037 and x is approximately equal to 0.55.
abstract: Structural aspects and electronic properties for the Fe(1 + δ)Se(1 - x)Te(x) system with 0.04 ≤ δ ≤ 0.08 and 0.5 ≤ x ≤ 1, especially with the superconducting composition δ is approximately equal to 0.037 and x is approximately equal to 0.55, are investigated comprehensively with x-ray four-circle diffraction and through measurements of electrical resistivity, thermoelectric power, magnetic susceptibility and nuclear magnetic resonance for (125)Te. The crystal structures with an excess Fe site are refined precisely with obvious constraints. For the superconducting composition, the transport properties are explained in terms of the two-band model, where an electron carrier band gives a linear-in-T resistivity and another hole band leads to nearly temperature-independent behaviour. The magnetic susceptibility and the Knight shift are explained with the idea that the electron correlation is enhanced with increasing x and it is reduced with annealing. The spin-lattice relaxation rates for the normal state that show the apparent Korringa relation may also be understood in this framework. These evidences suggest that the superconductivity may emerge in a regime where the correlation is relatively weak in this system.
authors.affiliation: Institute of Physics, University of Tsukuba, Tennodai, Tsukuba, Japan. onoda.masashige.ft@u.tsukuba.ac.jp
authors.forename: Masashige
authors.initials: M
authors.lastname: Onoda
authors.forename: Yasuna
authors.initials: Y
authors.lastname: Kawasaki
authors.forename: Masashi
authors.initials: M
authors.lastname: Tsubokawa
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Koyano