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

arXiv · 1305.2705

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

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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 $1/^{75}T_1T$, first increase strongly with pressure but fall again at $P > P_{\rm opt} =$ 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.

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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. 2013-08-23. Simultaneous optimization of spin fluctuations and superconductivity under pressure in an iron-based superconductor. https://doi.org/10.1103/physrevlett.111.107004

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