Temperature-dependent quasiparticle conduction band structure of the EuS monolayer

The temperature-dependent quasiparticle band structure of a ferromagnetic EuS monolayer is calculated using the s-f model which combines the one-electron 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-binding linear muffin-tin orbital) band-structure calculation. A suitable supercell with five layers of empty spheres was used in the band-structure calculations to obtain the Bloch energies of the monolayer. We find striking correlation effects in the quasiparticle spectrum induced by the s-f exchange interaction and also observe significant temperature effects in the spectrum. 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 the monolayer and to analyse the influences of the low dimensionality on the quasiparticle spectrum of this system. The bulk spectrum also exhibits significant correlation and temperature effects. The conduction bands of the monolayer 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.