Novel Relationship between Antiferromagnetic Spin Fluctuations and Superconductivity in FeSe_0.47Te_0.53 under Pressure

The relationship between antiferromagnetic spin fluctuations, nematic fluctuations, and superconductivity has been central to understanding the pairing mechanism in iron-based superconductors. Iron chalcogenides, which hold the simplest crystal structure in iron-based superconductors, provide a good platform to investigate the relationship. Here, we report ⁷⁷Se and ¹²⁵Te nuclear magnetic resonance studies of FeSe_0.47Te_0.53, which is close to a pure nematic quantum critical point. Both the superconducting critical temperature and antiferromagnetic spin fluctuations were found to be enhanced under pressure, which suggests a correlation between superconductivity and antiferromagnetic spin fluctuations in FeSe_0.47Te_0.53. However, the contribution of antiferromagnetic spin fluctuations to superconductivity in FeSe_0.47Te_0.53 is much less compared to that in FeSe_1−xS_x [1]. Since superconductivity in FeSe_1−xS_x was widely believed to be mediated by antiferromagnetic spin fluctuations, the contrasting behavior of FeSe_0.47Te_0.53 should come from a different origin. Our study indicates that instead of antiferromagnetic spin fluctuations, nematic fluctuations play a dominant role in the superconductivity in FeSe_1−xTe_x.

[1] K. Rana, D. V. Ambika, S. L. Bud'ko, A. E. Böhmer, P. C. Canfield, and Y. Furukawa, Phys. Rev. B 107, 134507 (2023).