Fermi Surface and Band Renormalization in (Sr,K)Fe$_2$As$_2$   Superconductor from Angle-Resolved Photoemission Spectroscopy
  High resolution angle-resolved photoemission measurements have been carried out on (Sr,K)Fe$_2$As$_2$ superconductor (Tc=21 K). Three hole-like Fermi surface sheets are clearly resolved for the first time around the Gamma point. The overall electronic structure shows significant difference from the band structure calculations. Qualitative agreement between the measured and calculated band structure is realized by assuming a chemical potential shift of -0.2 eV. The obvious band renormalization suggests the importance of electron correlation in understanding the electronic structure of the Fe-based compounds. 
Haiyun Liu, Wentao Zhang, Lin Zhao, Xiaowen Jia, Jianqiao Meng,   Guodong Liu, Xiaoli Dong, G. F. Chen, J. L. Luo, N. L. Wan...