We use angle-resolved photo-emission spectroscopy (ARPES) to explore the electronic structure of single crystals of FeSe over a wide range of binding energies and study the effects of strong electron-electron correlations. We provide evidence for the existence of "Hubbard-like bands" at high binding energies consisting of incoherent many-body excitations originating from Fe 3d states in addition to the renormalized quasiparticle bands near the Fermi level. Many high energy features of the observed ARPES data can be accounted for when incorporating effects of strong local Coulomb interactions in calculations of the spectral function via dynamical mean-field theory, including the formation of a Hubbard-like band. This shows that over the energy scale of several eV, local correlations arising from the on-site Coulomb repulsion and Hund's coupling are essential for a proper understanding of the electronic structure of FeSe and other related iron based superconductors.

We investigate the role of non-local correlations in LiFeAs by exploring an ab-initio-derived multiorbital Hubbard model for LiFeAs via the Two-Particle Self-Consistent (TPSC) approach. The multi-orbital formulation of TPSC approximates the irreducible interaction vertex to be an orbitaldependent constant, which is self-consistently determined from local spin and charge sum rules. Within this approach, we disentangle the contribution of local and non-local correlations in LiFeAs and show that in the local approximation one recovers the dynamical-mean field theory (DMFT) result. The comparison of our theoretical results to most recent angular-resolved photoemission spectroscopy (ARPES) and de-Haas van Alphen (dHvA) data shows that non-local correlations in LiFeAs are decisive to describe the measured spectral function A( k, ω), Fermi surface and scattering rates. These findings underline the importance of non-local correlations and benchmark different theoretical approaches for iron-based superconductors. arXiv:1906.11853v1 [cond-mat.str-el]

We investigate via LDA+DMFT (local density approximation combined with dynamical mean field theory) the manifestation of correlation effects in a wide range of binding energies in the holedoped family of Fe-pnictides AFe2As2 (A = K, Rb, Cs) as well as the fictitious FrFe2As2 and a-axis stretched CsFe2As2. This choice of systems allows for a systematic analysis of the interplay of Hund's coupling JH and on-site Coulomb repulsion U in multi-orbital Fe-pnictides under negative pressure. With increasing ionic size of the alkali metal, we observe a non-trivial change in the iron 3d hoppings, an increase of orbitally-selective correlations and the presence of incoherent weight at high-binding energies that do not show the typical lower Hubbard-band behavior but rather characteristic features of a Hund's metal. This is especially prominent in a-stretched CsFe2As2. We also find that the coherent/incoherent electronic behavior of the systems is, apart from temperature, strongly dependent on JH and we provide estimates of the coherence scale T * . We discuss these results in the framework of reported experimental observations.Iron-based layered superconductor La[O1−xFx]FeAs (x = 0.05 − 0.12) with Tc = 26 K, J. Am. Chem. Soc. 130, 3296

We study the effect of oxygen vacancies on the electronic structure of the model strongly correlated metal SrVO3. By means of angle-resolved photoemission (ARPES) synchrotron experiments, we investigate the systematic effect of the UV dose on the measured spectra. We observe the onset of a spurious dose-dependent prominent peak at an energy range were the lower Hubbard band has been previously reported in this compound, raising questions on its previous interpretation. By a careful analysis of the dose dependent effects we succeed in disentangling the contributions coming from the oxygen vacancy states and from the lower Hubbard band. We obtain the intrinsic ARPES spectrum for the zero-vacancy limit, where a clear signal of a lower Hubbard band remains. We support our study by means of state-of-the-art ab initio calculations that include correlation effects and the presence of oxygen vacancies. Our results underscore the relevance of potential spurious states affecting ARPES experiments in correlated metals, which are associated to the ubiquitous oxygen vacancies as extensively reported in the context of a two-dimensional electron gas (2DEG) at the surface of insulating d 0 transition metal oxides. A major challenge of modern physics is to understand the fascinating phenomena in strongly-correlated transition metal oxides (TMOs), which emerge in the neighborhood of the Mott insulator state. Some preeminent examples that have gathered the interest for almost 30 years are high temperature superconductivity, colossal magnetoresistance, heavy fermion physics and, of course, the Mott metal-insulator transition itself [1]. Significant theoretical progress was made with the introduction of Dynamical Mean Field Theory (DMFT) and its combination with ab initio Density Functional methods (LDA+DMFT), which allows treatment of the interactions promoting itinerancy and localization of electrons on equal footing [2][3][4]. Among the most emblematic achievements of DMFT is the prediction of a Hubbard satellite, which splits off of the conduction band of a metal. This satellite results from the partial localization of conduction electrons due to their mutual Coulomb repulsion. Early DMFT studies also showed that it is the precursor of the localized electronic states of a Mott insulator [5]. Since then, these predictions promoted a large number of studies using photoemission spectroscopy, which is a technique to directly probe the presence of Hubbard bands. In this context, the TMO system SrVO 3 has emerged as the drosophila model system to test the predictions of strongly correlated electron theories. In fact, SrVO 3 is arguably the simplest correlated metal. It is a simple cubic perovskite, with nominally one electron per V site, which occupies a 3 fold degenerate t 2g conduction band. While the presence of a satellite in the photoemission spectra of Ni metal was already well known, in the context of correlated TMOs, the Hubbard band was originally reported in a systematic investigation of Ca 1−x Sr x VO 3 [6], which was follo...