Interrelationships between nematicity, antiferromagnetic spin fluctuations and superconductivity: Role of hotspots in FeSe${}_{1-x}$S${}_x$ revealed by high pressure ${}^{77}$Se NMR study

Abstract

The sulfur-substituted FeSe, FeSe${}_{1-x}$S${}_x$, is one of the unique systems that provides an independent tunability of nematicity, antiferromagnetism and superconductivity under pressure ($p$). Recently Rana et al. [Phys. Rev. B 101, 180503(R) (2020)] reported, from ${}^{77}$Se nuclear magnetic resonance (NMR) measurements on FeSe${}_{0.91}$S${}_{0.09}$ under pressure, that there exists a clear role of nematicity on the relationship between antiferromagnetic (AFM) spin fluctuations and superconducting transition temperature ($T_{\mathrm{c}}$) where the AFM spin fluctuations are more effective in enhancing $T_{\mathrm{c}}$ in the absence of nematicity than with nematicity. Motivated by the work, we carried out ${}^{77}$Se NMR measurements on FeSe${}_{1-x}$S${}_x$ with $x$= 0.15 and 0.29 under pressure up to 2.10 GPa to investigate the relationship in a wide range of $x$ in the FeSe${}_{1-x}$S${}_x$ system. Based on the new results together with the previously reported data for $x$=0 [P. Wiecki et al., Phys. Rev. B 96, 180502(R) (2017)] and 0.09 [K. Rana et al. Phys. Rev. B 101, 180503(R) (2020)], we established a $p$ - $x$ - temperature ($T$) phase diagram exhibiting the evolution of AFM spin fluctuations. From the systematic analysis of the NMR data, we found that the superconducting (SC) state in nematic state arises from a non Fermi liquid state with strong stripe-type AFM spin fluctuations while the SC state without nematicity comes from a Fermi liquid state with mild stripe-type AFM spin fluctuations. Furthermore, we show that the previously reported impact of nematicity on the relationship between AFM fluctuations and superconductivity holds throughout the wide range of $x$ from $x$ = 0 to 0.29 in FeSe${}_{1-x}$S${}_x$ under pressure. We discuss the origin of the role of nematicity in terms of the different numbers of hotspots on Fermi surfaces with and without nematicity.

11 pages, 9 figures, accepted for publication in Phys. Rev. B

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