title: Simultaneous optimization of spin fluctuations and superconductivity under pressure in an iron-based superconductor.
abstract: We present a high-pressure NMR study of the overdoped iron pnictide superconductor NaFe0.94Co0.06As. The low-energy antiferromagnetic spin fluctuations in the normal state, manifest as the Curie-Weiss upturn in the spin-lattice relaxation rate 1/(75)T1T, first increase strongly with pressure but fall again at P>Popt=2.2  GPa. Neither long-ranged magnetic order nor a structural phase transition is encountered up to 2.5 GPa. The superconducting transition temperature Tc shows a pressure dependence identical to the spin fluctuations. Our observations demonstrate that magnetic correlations and superconductivity are optimized simultaneously as a function of the electronic structure, thereby supporting very strongly a magnetic origin of superconductivity.
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, China.
authors.forename: G F
authors.initials: GF
authors.lastname: Ji
authors.affiliation: School of Energy, Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China.
authors.forename: J S
authors.initials: JS
authors.lastname: Zhang
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, China.
authors.forename: Long
authors.initials: L
authors.lastname: Ma
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, China.
authors.forename: P
authors.initials: P
authors.lastname: Fan
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, China.
authors.forename: P S
authors.initials: PS
authors.lastname: Wang
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, China.
authors.forename: J
authors.initials: J
authors.lastname: Dai
authors.affiliation: Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA.
authors.forename: G T
authors.initials: GT
authors.lastname: Tan
authors.affiliation: Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA and Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Song
authors.affiliation: Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA and Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Zhang
authors.affiliation: Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA and Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Dai
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, China.
authors.forename: B
authors.initials: B
authors.lastname: Normand
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, China.
authors.forename: Weiqiang
authors.initials: W
authors.lastname: Yu