Angle-resolved spectroscopy study of Ni-based superconductor   SrNi$_2$As$_2$
  We performed an angle-resolved photoemission spectroscopy study of the Ni-based superconductor SrNi$_2$As$_2$. Electron and hole Fermi surface pockets are observed, but their different shapes and sizes lead to very poor nesting conditions. The experimental electronic band structure of SrNi$_2$As$_2$ is in good agreement with first-principles calculations after a slight renormalization (by a factor 1.1), confirming the picture of Hund's exchange-dominated electronic correlations decreasing with increasing filling of the $3d$ shell in the Fe-, Co- and Ni-based compounds. These findings emphasize the importance of Hund's coupling and $3d$-orbital filling as key tuning parameters of electronic correlations in transition metal pnictides. 
L.-K. Zeng, P. Richard, A. van Roekeghem, J.-X. Yin, S.-F. Wu, Z. G.   Chen, N. L. Wang, S. Biermann, T. Qian and H. Ding
cond-mat.supr-con cond-mat.str-el