Electronic structure of ${\mathrm{MoSe}}_2$, ${\mathrm{MoS}}_2$, and ${\mathrm{WSe}}_2$. I. Band-structure calculations and photoelectron spectroscopy

The band structures of the semiconducting layered compounds ${\mathrm{MoSe}}_2$, ${\mathrm{MoS}}_2$, and ${\mathrm{WSe}}_2$ have been calculated self-consistently with the augmented-spherical-wave method. Angle-resolved photoelec- tron spectroscopy of ${\mathrm{MoSe}}_2$ using He i, He ii, and Ne i radiation, and photon-energy-dependent normal-emission photoelectron spectroscopy using synchrotron radiation, show that the calculational results give a good description of the valence-band structure. At about 1 eV below the top of the valence band a dispersionless state was measured, almost completely of Mo 4d character. Such a state, which is not predicted by band-structure calculations, has also been observed in metallic layered compounds. Suggestions are given for the explanation of this phenomenon.