title: Correlation-induced self-doping in the iron-pnictide superconductor Ba2Ti2Fe2As4O.
abstract: The electronic structure of the iron-based superconductor Ba2Ti2Fe2As4O (Tc(onset)=23.5  K) has been investigated by using angle-resolved photoemission spectroscopy and combined local density approximation and dynamical mean field theory calculations. The electronic states near the Fermi level are dominated by both the Fe 3d and Ti 3d orbitals, indicating that the spacer layers separating different FeAs layers are also metallic. By counting the enclosed volumes of the Fermi surface sheets, we observe a large self-doping effect; i.e., 0.25 electrons per unit cell are transferred from the FeAs layer to the Ti2As2O layer, leaving the FeAs layer in a hole-doped state. This exotic behavior is successfully reproduced by our dynamical mean field calculations, in which the self-doping effect is attributed to the electronic correlations in the 3d shells. Our work provides an alternative route of effective doping without element substitution for iron-based superconductors.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: J-Z
authors.initials: JZ
authors.lastname: Ma
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and Centre de Physique Théorique, Ecole Polytechnique, CNRS-UMR7644, 91128 Palaiseau, France.
authors.forename: A
authors.initials: A
authors.lastname: van Roekeghem
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and Collaborative Innovation Center of Quantum Matter, Beijing, China.
authors.forename: P
authors.initials: P
authors.lastname: Richard
authors.affiliation: Department of Physics, Renmin University, Beijing 100872, China.
authors.forename: Z-H
authors.initials: ZH
authors.lastname: Liu
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: H
authors.initials: H
authors.lastname: Miao
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: L-K
authors.initials: LK
authors.lastname: Zeng
authors.affiliation: Paul Scherrer Institute, Swiss Light Source, CH-5232 Villigen PSI, Switzerland.
authors.forename: N
authors.initials: N
authors.lastname: Xu
authors.affiliation: Paul Scherrer Institute, Swiss Light Source, CH-5232 Villigen PSI, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Shi
authors.affiliation: Department of Physics, Condensed Matter Physics Group, Hangzhou Normal University, Hangzhou 310036, China.
authors.forename: C
authors.initials: C
authors.lastname: Cao
authors.affiliation: Department of Physics, Renmin University, Beijing 100872, China.
authors.forename: J-B
authors.initials: JB
authors.lastname: He
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and Collaborative Innovation Center of Quantum Matter, Beijing, China and Department of Physics, Renmin University, Beijing 100872, China.
authors.forename: G-F
authors.initials: GF
authors.lastname: Chen
authors.affiliation: Department of Physics, Zhejiang University, Hangzhou 310027, China.
authors.forename: Y-L
authors.initials: YL
authors.lastname: Sun
authors.affiliation: Department of Physics, Zhejiang University, Hangzhou 310027, China.
authors.forename: G-H
authors.initials: GH
authors.lastname: Cao
authors.affiliation: Department of Physics, Renmin University, Beijing 100872, China.
authors.forename: S-C
authors.initials: SC
authors.lastname: Wang
authors.affiliation: Centre de Physique Théorique, Ecole Polytechnique, CNRS-UMR7644, 91128 Palaiseau, France and Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France and European Theoretical Synchrotron Facility (ETSF), Europe.
authors.forename: S
authors.initials: S
authors.lastname: Biermann
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: T
authors.initials: T
authors.lastname: Qian
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and Collaborative Innovation Center of Quantum Matter, Beijing, China.
authors.forename: H
authors.initials: H
authors.lastname: Ding