Electronic structure and exotic exchange splitting in spin-density-wave   states of BaFe$_2$As$_2$
  The magnetic properties in the parent compounds are often intimately related to the microscopic mechanism of superconductivity. Here we report the first direct measurements on the electronic structure of a parent compound of the newly discovered iron-based superconductor, BaFe$_2$As$_2$, which provides a foundation for further studies. We show that the energy of the spin density wave (SDW) in BaFe$_2$As$_2$ is lowered through exotic exchange splitting of the band structure, rather than Fermi surface nesting of itinerant electrons. This clearly demonstrates that a metallic SDW state could be solely induced by interactions of local magnetic moments, resembling the nature of antiferromagnetic order in cuprate parent compounds. 
L. X. Yang, Y. Zhang, H. W. Ou, J. F. Zhao, D. W. Shen, B. Zhou, J.   Wei, F. Chen, M. Xu, C. He, Y. Chen, Z. D. Wang, X. F....