Figure 1: Brillouin zone symmetry and 3D Dirac cone.

(a) Cd₃As₂ crystalizes in a tetragonal body centre structure with space group of I4₁cd, which has 32 number of formula units in the unit cell. The tetragonal structure has lattice constant of a=12.670 Å, b=12.670 Å and c=25.480 Å. (b) The basic structure unit is a four corner-sharing CdAs₃-trigonal pyramid. (c) Core-level spectroscopic measurement where Cd 4d and As 3d peaks are clearly observed. Inset shows a picture of the Cd₃As₂ samples used for angle-resolved photoemission spectroscopy (ARPES) measurements. The flat and mirror-like surface indicate the high quality of our samples. (d) The bulk BZ and the projected surface BZ along the (001) direction. The red crossings locate at (k_x, k_y, k_z)=(0, 0, 0.15(2π)/(c*)) (c*=c/a). They denote the two special k points along the Γ−Z momentum space cut-direction, where 3D Dirac band-touchings are protected by the crystalline C₄ symmetry along the k_z axis. (e) Second derivative image of ARPES dispersion map of Cd₃As₂ over the wider binding energy range. Various bands are well-resolved up to 3 eV binding energy range. (f) ARPES E_B−k_x cut of Cd₃As₂ near the Fermi level at around surface BZ centre point.