Simultaneous optimization of spin fluctuations and superconductivity under pressure in an iron-based superconductor

G F Ji; J S Zhang; Long Ma; P Fan; P S Wang; J Dai; G T Tan; Y Song; C L Zhang; Pengcheng Dai; B Normand; Weiqiang Yu

doi:10.1103/PhysRevLett.111.107004

Simultaneous optimization of spin fluctuations and superconductivity under pressure in an iron-based superconductor

Phys Rev Lett. 2013 Sep 6;111(10):107004. doi: 10.1103/PhysRevLett.111.107004. Epub 2013 Sep 4.

Authors

G F Ji¹, J S Zhang², Long Ma¹, P Fan¹, P S Wang¹, J Dai¹, G T Tan³, Y Song⁴, C L Zhang⁴, Pengcheng Dai⁴, B Normand¹, Weiqiang Yu¹

Affiliations

¹ Department of Physics, Renmin University of China, Beijing 100872, China.
² School of Energy, Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China.
³ Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA.
⁴ 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.

PMID: 25166698
DOI: 10.1103/PhysRevLett.111.107004

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.