Opposite dispersion bands at the Fermi level in ZrSe2

The electronic structure of ZrSe2 was studied by high resolution angular resolved photoemission spectroscopy (ARPES) and by density functional theory (DFT). ARPES with distinct horizontal (P) and vertical (S)-polarized synchrotron radiation was performed on the sample kept at room temperature and 20 K to unravel the electronic structure especially at the Fermi energy (EF). The DFT calculations including spin-orbit coupling using the modified Becke-Johnson potential reveal the presence of three occupied valence bands at the Γ(A)-point and show that the minimum indirect bandgap is between the Γ- and L-points of the Brillouin zone (BZ) similar to the experimental results. While the DFT calculations give only a single conduction band at the L and M-points of the BZ, the ARPES data (20 K) show two bands with opposite dispersion at EF. The observation of two bands close to EF was already reported in the charge density wave phase of TiSe2. The underlying mechanism of our observations is possibly a folding of the...