On the origin of the shallow and "replica" bands in FeSe monolayer superconductors

Abstract

We compare electronic structures of single FeSe layer films on SrTiO${}_3$ substrate (FeSe/STO) and K${}_x$Fe${}_{2-y}$Se${}_2$ superconductors obtained from extensive LDA and LDA+DMFT calculations with the results of ARPES experiments. It is demonstrated that correlation effects on Fe-3d states are sufficient in principle to explain the formation of the shallow electron -- like bands at the M(X)-point. However, in FeSe/STO these effects alone are apparently insufficient for the simultaneous elimination of the hole -- like Fermi surface around the $\Gamma$-point which is not observed in ARPES experiments. Detailed comparison of ARPES detected and calculated quasiparticle bands shows reasonable agreement between theory and experiment. Analysis of the bands with respect to their origin and orbital composition shows, that for FeSe/STO system the experimentally observed "replica" quasiparticle band at the M-point (usually attributed to forward scattering interactions with optical phonons in SrTiO${}_3$ substrate) can be reasonably understood just as the LDA calculated Fe-3d${}_{xy}$ band, renormalized by electronic correlations. The only manifestation of the substrate reduces to lifting the degeneracy between Fe-3d${}_{xz}$ and Fe-3d${}_{yz}$ bands in the vicinity of M-point. For the case of K${}_x$Fe${}_{2-y}$Se${}_2$ most bands observed in ARPES can also be understood as correlation renormalized Fe-3d LDA calculated bands, with overall semi -- quantitative agreement with LDA+DMFT calculations.

8 pages, 5 figures

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• Heterostructural one-unit-cell FeSe/SrTiO3: from high-temperature superconductivity to topological states
• Electronic structure of FeSe monolayer superconductors: shallow bands and correlations
• Electronic and phononic properties of a two dimensional electron gas coupled to dipolar phonons via small-momentum-transfer scattering
• Electron - phonon coupling in Eliashberg - McMillan theory beyond adiabatic approximation
• Antiadiabatic phonons, Coulomb pseudopotential and superconductivity in Eliashberg - McMillan theory
• Possible spin excitation structure in monolayer FeSe grown on SrTiO${}_3$
• Strong enhancement of magnetic order from bulk to stretched monolayer FeSe as Hund's metals
• Effect of the additional Se layer on the electronic structure of iron-based superconductor FeSe/SrTiO${}_3$
• Hidden Fermi surface in K${}_x$Fe${}_{2-y}$Se${}_2$: LDA+DMFT study