“…Thus, for FeSe/STO system we observe the general agreement between the results of LDA+DMFT calculations of Ref. [54] (Fig. 12(h)) and ARPES data [63] ( Fig.…”
Section: Lda+dmft Resultssupporting
confidence: 85%
“…LDA+DMFT spectral function maps[54] for different Fe-3d orbitals of FeSe monolayer on SrTiO3 substrate (top) and isolated FeSe monolayer (bottom): (a) -Fe-3dxz and Fe-3dyz, (b) -Fe-3dxy, (c) -Fe-3d 3z 2 −r 2 , (d) -Fe-3d x 2 −y 2 . Fermi level is at zero energy.…”
Electronic spectra of typical single FeSe layer superconductors -FeSe monolayer films on SrTiO3 substrate (FeSe/STO) and KxFe2−ySe2 obtained from ARPES data reveal several puzzles: what is the origin of shallow and the so called "replica" bands near M-point and why the hole-like Fermi surfaces near Γ-point are absent. Our extensive LDA+DMFT calculations show that correlation effects on Fe-3d states can almost quantitatively reproduce rather complicated band structure, which is observed in ARPES, in close vicinity of the Fermi level for FeSe/STO and KxFe2−ySe2. Rather unusual shallow electron-like bands around the M(X)-point in the Brillouin zone are well reproduced. However, in FeSe/STO correlation effects are apparently insufficient to eliminate the hole-like Fermi surfaces around the Γ-point, which are not observed in most ARPES experiments. Detailed analysis of the theoretical and experimental quasiparticle bands with respect to their origin and orbital composition is performed. It is shown that for FeSe/STO system the LDA calculated Fe-3dxy band, renormalized by electronic correlations within DMFT gives the quasiparticle band almost exactly in the energy region of the experimentally observed "replica" quasiparticle band at the M-point. For the case of KxFe2−ySe2 most bands observed in ARPES can also be understood as correlation renormalized Fe-3d LDA calculated bands, with overall semi-quantitative agreement with our LDA+DMFT calculations. Thus the shallow bands near the M-point are common feature for FeSebased systems, not just FeSe/STO. We also present some simple estimates of "forward scattering" electron-optical phonon interaction at FeSe/STO interface, showing that it is apparently irrelevant for the formation of "replica" band in this system and significant increase of superconducting Tc.
“…Thus, for FeSe/STO system we observe the general agreement between the results of LDA+DMFT calculations of Ref. [54] (Fig. 12(h)) and ARPES data [63] ( Fig.…”
Section: Lda+dmft Resultssupporting
confidence: 85%
“…LDA+DMFT spectral function maps[54] for different Fe-3d orbitals of FeSe monolayer on SrTiO3 substrate (top) and isolated FeSe monolayer (bottom): (a) -Fe-3dxz and Fe-3dyz, (b) -Fe-3dxy, (c) -Fe-3d 3z 2 −r 2 , (d) -Fe-3d x 2 −y 2 . Fermi level is at zero energy.…”
Electronic spectra of typical single FeSe layer superconductors -FeSe monolayer films on SrTiO3 substrate (FeSe/STO) and KxFe2−ySe2 obtained from ARPES data reveal several puzzles: what is the origin of shallow and the so called "replica" bands near M-point and why the hole-like Fermi surfaces near Γ-point are absent. Our extensive LDA+DMFT calculations show that correlation effects on Fe-3d states can almost quantitatively reproduce rather complicated band structure, which is observed in ARPES, in close vicinity of the Fermi level for FeSe/STO and KxFe2−ySe2. Rather unusual shallow electron-like bands around the M(X)-point in the Brillouin zone are well reproduced. However, in FeSe/STO correlation effects are apparently insufficient to eliminate the hole-like Fermi surfaces around the Γ-point, which are not observed in most ARPES experiments. Detailed analysis of the theoretical and experimental quasiparticle bands with respect to their origin and orbital composition is performed. It is shown that for FeSe/STO system the LDA calculated Fe-3dxy band, renormalized by electronic correlations within DMFT gives the quasiparticle band almost exactly in the energy region of the experimentally observed "replica" quasiparticle band at the M-point. For the case of KxFe2−ySe2 most bands observed in ARPES can also be understood as correlation renormalized Fe-3d LDA calculated bands, with overall semi-quantitative agreement with our LDA+DMFT calculations. Thus the shallow bands near the M-point are common feature for FeSebased systems, not just FeSe/STO. We also present some simple estimates of "forward scattering" electron-optical phonon interaction at FeSe/STO interface, showing that it is apparently irrelevant for the formation of "replica" band in this system and significant increase of superconducting Tc.
“…3b and e, no hole FS is shown around M. Around Γ, on the other hand, two small hole FS exist for undoped ML FeSe, while they sink below the E F for the doped case. Consequently, no hole surface is present for the doped ML FeSe, in agreement with experimental observations on ML FeSe/ SrTiO 3 system 16,17,22,36 as well as previous DFT+DMFT calculations 37,38 . In Fig.…”
Despite of the importance of magnetism in possible relation to other key properties in iron-based superconductors, its understanding is still far from complete especially for FeSe systems. On one hand, the origin of the absence of magnetic orders in bulk FeSe is yet to be clarified. On the other hand, it is still not clear how close monolayer FeSe on SrTiO3, with the highest transition temperature among iron-based superconductors, is to a magnetic instability. Here we investigate magnetic properties of bulk and monolayer FeSe using dynamical mean-field theory combined with density-functional theory. We find that suppressed magnetic order in bulk FeSe is associated with the reduction of interorbital charge fluctuations, an effect of Hund’s coupling, enhanced by a larger crystal-field splitting. Meanwhile, spatial isolation of Fe atoms in expanded monolayer FeSe leads into a strong magnetic order, which is completely destroyed by a small electron doping. Our work provides a comprehensive understanding of the magnetic order in iron-based superconductors and other general multi-orbital correlated systems as Hund’s metals.
“…1f). The isotope dependences of E S ( E S *) and Ω 1 (Ω 2 ) constitute compelling evidence that the replica bands are due to shake-off excitations with the STO phonons, and exclude the scenario that the replica band is merely a renormalize d 3 d xy band 22 .Fig. 1Isotope dependence of the phonon features.…”
Section: Resultsmentioning
confidence: 80%
“…However, the lack of direct evidence has touched off turbulent debates on whether interfacial EPI exists across the interface and how it relates to the high T c in FeSe/STO. These range from whether the replica band is simply a renormalized d xy band 22 or due to phonon shake-off effects, to whether the shake-off is related to initial-state effects or to the ejected photoelectrons 23 . Moreover, supposing the existence of interfacial EPI, there remains substantial debate as to whether and how interfacial EPI relates to the superconductivity 6,18,19,23–29 .…”
At the interface between monolayer FeSe films and SrTiO3 substrates the superconducting transition temperature (Tc) is unexpectedly high, triggering a surge of excitement. The mechanism for the Tc enhancement has been the central question, as it may present a new strategy for seeking out higher Tc materials. To reveal this enigmatic mechanism, by combining advances in high quality interface growth, 16O
18O isotope substitution, and extensive data from angle resolved photoemission spectroscopy, we provide striking evidence that the high Tc in FeSe/SrTiO3 is the cooperative effect of the intrinsic pairing mechanism in the FeSe and interactions between the FeSe electrons and SrTiO3 phonons. Furthermore, our results point to the promising prospect that similar cooperation between different Cooper pairing channels may be a general framework to understand and design high-temperature superconductors.
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