Strong multiple resonances in the photoemission spectra of transition-metal-layer and misfit-layer compounds

Abstract

Photoelectron spectra as a function of photon energy are presented for the valence band of three misfit-layer compounds (SnS${)}_{1+\mathrm{\ensuremath{\delta}}}$T${\mathrm{S}}_{2}$ (T=Ti, Nb, Ta, and \ensuremath{\delta}=0.20, 0.17, and 0.16, respectively). The spectra of the misfit-layer compounds are compared with the spectra of SnS, ${\mathrm{TiS}}_{2}$, ${\mathrm{NbS}}_{2}$, and ${\mathrm{TaS}}_{2}$. In all transition-metal compounds strong multiple resonances are observed for the photoemission of electrons from the transition-metal d states of the T${\mathrm{S}}_{2}$ layers. The dispersion of the sulphur 3${\mathit{p}}_{\mathit{z}}$ states along the z axis normal to the layers, observed in the transition-metal compounds, is absent in the misfit-layer compounds, as a consequence of the alternated stacking. We found evidence for a plasmon contribution to the resonances in the photoemission intensity. Finally, the chemical bonding between the layers in the misfit-layer compounds is discussed. It is shown that the interlayer interaction is of covalent character and that there is no charge transfer from one layer to the other.