Electronic properties of CaFe$_{2}$As$_{2}$

CaFe$_{2}$As$_{2}$ is a parent compound of a new family of FeAs based high-$T_{c}$ superconductors. It undergoes a first-order structural transition from low-$T$ orthorhombic to high-$T$ tetragonal phase [Ni \textit{et al.}, Phys. Rev. B \textbf{78}, 014523]. Moderate pressure lowers the transition temperature, and turns on the superconductivity [Torikachvili \textit{et al.}, Phys. Rev. Lett. \textbf{101}, 057006]. Study on its electronic properties is of crucial importance for understanding the pairing mechanism of the FeAs based superconductors. Here we present angle-resolved photoemission spectroscopy (ARPES) results on both the orthorhombic and the tetragonal phase of CaFe$_{2}$As$_{2}$. In the orthorhombic phase, we find strong $k_{z}$ dispersion on the Fermi surfaces, showing a three dimensional electronic structure. We also find dramatic difference of the Fermi surface structure between the orthorhombic and the tetragonal phase.