Hidden Fermi Surface in KxFe2–ySe2: LDA + DMFT Study

Abstract

In this paper we provide theoretical LDA + DMFT support of recent angle-resolved photoemission spectroscopy (ARPES) observation of the so-called hidden hole-like band and corresponding hidden Fermi surface sheet near Γ-point in the K_0.62Fe_1.7Se₂ compound. To some extent, this is a solution to the long-standing riddle of Fermi surface absence around Γ-point in the K_xFe_2–ySe₂ class of iron chalcogenide superconductors. In accordance with the experimental data, Fermi surface was found near the Γ-point within LDA + DMFT calculations. Based on the LDA + DMFT analysis in this paper it is shown that the largest of the experimental Fermi surface sheets is actually formed by a hybrid Fe-3d ( xy, xz, yz )quasiparticle band. It is also shown that the Fermi surface is not a simple circle as DFT-LDA predicts, but has (according to the LDA + DMFT) a more complicated “propeller”-like structure due to correlations and multiorbital nature of the K_xFe_2–ySe₂ materials. While the smallest experimental Fermi surface around Γ-point is in some sense fictitious, since it is formed by the summation of the intensities of the spectral function associated with “propeller” loupes and is not connected to any of quasiparticle bands.