Fig. 1: Fermi surface and AFM Dirac line in YMn2Ge2.
a The crystal structure of YMn2Ge2. The purple arrows indicate that the two adjacent ferromagnetic Mn layers have opposite spin directions. b Bulk and surface Brillouin zones (BZs) of YMn2Ge2. High symmetry points are marked. The magnetic nodal line around the boundary of the BZ is highlighted by the green line. c ARPES Fermi surface spectrum on the (001) surface. The black square represents the surface BZ. Red dashed lines indicate ARPES dispersion cuts 1–3 in (e–j). d Calculated Fermi surface map corresponding to the black box in c and integrated over all the kz values. The same plot is also embedded in c. ARPES dispersion map (e), and the corresponding bulk band structure calculation (f) along cut 1 in (c). SS stands for surface state. High symmetry points are marked. Mn \({d}_{{z}^{2}}\) (blue) and \({d}_{{{{\rm{xy}}}}}\) (red) orbitals are projected on the bulk bands. The Fermi level in (f) is adjusted according to the experimental data and DFT is renormalized by 3. Two doubly degenerate bands cross at the A point to form a fourfold degeneracy. Thick red dashed line shows that the binding energy of the Dirac crossing at the A point in the renormalized DFT differs from experimental data. ARPES dispersion map (g), and the corresponding bulk band structure calculation (h) along cut 2 in (c). A fourfold Dirac crossing can be seen at the R point. The thick red dashed line shows the consistency between the renormalized DFT and experimental data especially at the R point. ARPES dispersion map (i), and the corresponding bulk band structure calculation (j) along cut 3 in (c). Thick red dashed lines suggest that although the renormalized DFT correctly describes the band dispersion near the R point, it doesn’t agree well with ARPES data at the A point. Black arrow in (j) indicates the nodal line, and A and R points consist of mostly \({d}_{{z}^{2}}\) and \({d}_{{xy}}\) orbitals, respectively.
