(color online) K_z measurements and Dirac line node in ZrSiS. (a) Plot of the constant energy contour at in –k_z space. The bulk and surface state bands are indicated by the red and green arrows, respectively. Magenta dotted lines indicate the k_z positions of four representing cuts shown in (b) and (d). (b) Detailed analysis of the four representing cuts, the surface bands and linear dispersions are marked. (c) The 3D BZ shows the constant energy contours (k_y–k_z plane and k_x–k_y plane) around the DP and illustrates the location of the Dirac line node (green solid line) in ZrSiS (X–R direction). (d) (i) Schematic of the Dirac line node along the k_z direction (labelled by the green curve) with the grey planes which are corresponding to each cut in (b) and (d) (ii). The bright curves sketch the Dirac dispersions we observe in each cut as in (ii). (ii) Stack plot of the four cuts as in (b). Green curve indicates the dispersion of the Dirac line node. (e) The fitted DP positions (red dots) at various k_z values, the green curve indicates the calculated dispersion along the X–R direction.