1204.2434 (Z. Li et al.)

Microscopic coexistence of antiferromagnetic order and superconductivity
in Ba$_{0.77}$K$_{0.23}$Fe$_{2}$As$_{2}$    [PDF]

Z. Li, R. Zhou, D. L. Sun, J. Yang, C. T. Lin, Guo-qing Zheng

The relationship between antiferromagnetism (AFM) and superconductivity (SC) is an important subject in condensed-matter physics. In heavy-fermion compounds, AFM and SC coexist microscopically. The same is true in some cuprate high-temperature superconductors. In the recently-discovered iron-pnictides, it is unclear whether AFM and SC can coexist or they compete one another. Here we address the issue by 75As nuclear magnetic resonance (NMR) measurements on single-crystal Ba0.77K0.23Fe2As2. Below T_N=46 K, we find that the NMR transition lines for H//c split and those for H//a shift, indicating that AFM sets in, with the ordered moment lying on the ab-plane. The spin lattice relaxation rate measured in the ordered state shows a distinct decrease below Tc(H=12 T)=16 K, following a T^3 relation. Our results show unambiguously that the electrons hyperfine-coupled to 75As-nuclei are responsible for both AFM and SC. Furthermore, the ordered moment is unchanged below Tc, indicating that AFM and SC do not compete but coexist microscopically.

View original: http://arxiv.org/abs/1204.2434