Electronic band structure of AlB2 studied by angle-resolved photoemission spectroscopy

We have performed UV and X-ray angle-resolved photoemission spectroscopy (ARPES) on AlB2 which is a non-superconducting reference of MgB2. We found that the sigma-band is totally occupied in AlB2 in contrast to the partially occupied sigma-band in MgB2, which suggests that the sigma-band on the Fermi level is essential for the superconductivity. We also found an electron pocket centered at the Γ (A) point in the UVARPES spectrum as in MgB2, while it is absent in the X-ray ARPES spectra. This indicates that the electron pocket is of surface origin