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 NaFe${}_{0.94}$Co${}_{0.06}$As. The low-energy antiferromagnetic spin fluctuations in the normal state, manifest as the Curie-Weiss upturn in the spin-lattice relaxation rate $1{/}^{75}{T}_{1}T$, first increase strongly with pressure but fall again at $P>P_{\mathrm{opt}}=$ 2.2 GPa. Neither long-ranged magnetic order nor a structural phase transition is encountered up to 2.5 GPa. The superconducting transition temperature $T_c$ 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.

Accepted for publication in Physical Review Letters

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• Nearly-critical spin and charge fluctuations in KFe2As2 observed by high-pressure NMR
• Origin of doping-induced suppression and reemergence of magnetism in LaFeAsO${}_{1-x}$H${}_x$
• Experimental evidence of $T_c$ enhancement without the influence of spin fluctuations: NMR study on LaFeAsO_{1-x}H_x under a pressure of 3.0 GPa
• NMR evidence for an intimate relationship between antiferromagnetic spin fluctuations and extended s-wave superconductivity in mono-crystalline SrFe2(As_{1-x}P_{x})2
• Phase Separation, Competition, and Volume Fraction Control in NaFe${}_{1-x}$Co${}_x$As
• Tuning the interplay between nematicity and spin fluctuations in Na${}_{1-x}$Li${}_x$FeAs superconductors
• Strong enhancement of magnetic order from bulk to stretched monolayer FeSe as Hund's metals
• Universal relationship between low-energy antiferromagnetic fluctuations and superconductivity in BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• Unification of the Pressure and Composition Dependence of Superconductivity in Ru substituted BaFe2As2
• Magnetic fluctuation and dominant superconducting pairing symmetry near the tunable Van Hove singularity