Temperature-dependent quasiparticle conduction band structure of the EuS monolayer

The temperature-dependent quasiparticle band structure of a ferromagnetic E uS monolayer is calculated using the s-f model which combines the one-elect ron band structure and a many-body model evaluation. The one-electron part required for the many-body calculation was obtained from a TB-LMTO (tight-b inding linear muffin-tin orbital) band-structure calculation. A suitable su percell with five layers of empty spheres was used in the band-structure ca lculations to obtain the Bloch energies of the monolayer. We find striking correlation effects in the quasiparticle spectrum induced by the s-f exchan ge interaction and also observe significant temperature effects in the spec trum. We have further calculated the quasiparticle spectrum of the bulk EuS using the same s-f model in order to compare the results with those for th e monolayer and to analyse the influences of the low dimensionality on the quasiparticle spectrum of this system. The bulk spectrum also exhibits sign ificant correlation and temperature effects. The conduction bands of the mo nolayer as well as the bulk EuS show red-shift with respect to temperature and the magnitude of the red-shift is found to be larger for some bands in the bulk EuS compared to that of the monolayer.