title: Antiferromagnetic spin fluctuations and unconventional nodeless superconductivity in an iron-based new superconductor (Ca4Al2O(6-y))(Fe2As2): 75As nuclear quadrupole resonance study.
abstract: We report 75As nuclear quadrupole resonance studies on (Ca4Al2O(6-y))(Fe2As2) with T(c) = 27  K. Measurement of nuclear-spin-relaxation rate 1/T1 has revealed a significant development of two-dimensional antiferromagnetic spin fluctuations down to T(c) in association with the smallest As-Fe-As bond angle. Below T(c), the temperature dependence of 1/T1 without any trace of the coherence peak is well accounted for by a nodeless s(±)-wave multiple-gaps model. From the fact that its T(c) is comparable to T(c) = 28  K in the optimally doped LaFeAsO(1-y) in which antiferromagnetic spin fluctuations are not dominant, we remark that antiferromagnetic spin fluctuations are not a unique factor for enhancing T(c) among Fe-based superconductors, but a condition for optimizing superconductivity should be addressed from the lattice structure point of view.
authors.affiliation: Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan. kinouchi@nmr.mp.es.osaka-u.ac.jp
authors.forename: H
authors.initials: H
authors.lastname: Kinouchi
authors.forename: H
authors.initials: H
authors.lastname: Mukuda
authors.forename: M
authors.initials: M
authors.lastname: Yashima
authors.forename: Y
authors.initials: Y
authors.lastname: Kitaoka
authors.forename: P M
authors.initials: PM
authors.lastname: Shirage
authors.forename: H
authors.initials: H
authors.lastname: Eisaki
authors.forename: A
authors.initials: A
authors.lastname: Iyo