Se NMR*

Magnetic fluctuations and/or nematic fluctuations are considered to be candidates for the pairing mechanism in unconventional superconductors such as iron pnictide superconductors. Quite recently nuclear magnetic resonance (NMR) measurements revealed strong correlation between superconductivity and antiferromagnetic (AFM) fluctuations despite being near a nematic quantum critical point in FeSe_1−xS_x [1]. To understand the quantitative relationship between superconductivity and magnetic fluctuations, we carried out ⁷⁷Se NMR on the optimally doped FeSe_0.9S_0.1 under pressure. In this presentation, we will report the NMR results, especially temperature dependence of nuclear spin lattice relaxation rate under different pressures. Upon analyzing the new together with the previous data [1,2] we will discuss the relationship between AFM fluctuations and superconductivity in the system.

[1] P. Wiecki, et al., Phys. Rev. B 98, 020507(R) (2018).
[2] P. Wiecki, et al., Phys. Rev. B 96, 180502(R) (2017).