ARPES measurements of SnAs electronic band structure

We report experimental study of the electronic band structure of SnAs superconductor with the NaCl type lattice structure by angular resolved photoelectron spectroscopy (ARPES). The determined band structure, in general, is in a good agreement with the calculated one. However, at odd with the calculated band structure, the experimental data reveals splitting of one of the upper valence bands into three branches along the $\bar{K}-\bar{\Gamma}-\bar{K}$ and $\bar{M}-\bar{\Gamma}-\bar{M^\prime}$ symmetry directions. We assume this splitting can be caused by the spin orbit coupling of electrons or a mixed valence of Sn atoms in the compound.