Multiple superconducting gaps and anisotropic spin fluctuations in iron-pnictides revealed by nuclear magnetic resonance

This article reviews nuclear magnetic resonance studies on iron-based high critical temperature superconductors carried out by the author's group. The Cooper pairs are in the spin-singlet state, and it was found for the first time that there exist multiple superconducting gaps. The antiferromagnetic spin fluctuations are anisotropic in spin space, and their role in producing superconductivity is of great interest.