Fig. 4: Drumhead surface state associated with the AFM nodal line.

a Semi-infinite surface calculations along the \(\bar{{{{\rm{X}}}}}\)-\(\bar{\Gamma }\)-\(\bar{{{{\rm{X}}}}}\) high symmetry direction. Color bar shows the surface state contribution. Red dashed lines are the bulk states on the A-R-Z plane. Black and red arrows represent the drumhead surface states associated with the AFM nodal line and the bulk state on the A-R-Z plane, respectively. Black dashed line marks the experimental Fermi level. SS and DP mean surface state and Dirac point, respectively. b ARPES dispersion map along the R-Z-R high symmetry direction. A high-resolution dispersion map (same as cut 2 in Fig. 1) at the center of the Brillouin zone (Z point) is embedded to highlight the surface and bulk states. Red and black dashed lines demonstrate the bulk Dirac crossing and the drumhead surface state at R point, respectively. Red arrows are the bulk states in (a) and black arrows represent the drumhead surface state also marked in (a). c Extracted dispersions of the bulk (red dots) and drumhead surface states (black dots) near the Fermi level. Error bars correspond to the experimental momentum and energy resolutions. Black dashed lines are the linear (left) and quadratic (right) fits to the ARPES data. d Illustration of the energy dispersion of the drumhead surface states near the Fermi level.