Correlation-induced self-doping in the iron-pnictide superconductor Ba2Ti2Fe2As4O

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• Iron-based superconductors exhibit complex electronic properties.
• Understanding the interplay between electronic structure and superconductivity is crucial.
• Ba2Ti2Fe2As4O is a notable iron-based superconductor with a Tc(onset) of 23.5 K.

Purpose of the Study:

• To investigate the electronic structure of Ba2Ti2Fe2As4O.
• To elucidate the mechanism behind its superconducting properties.
• To explore novel doping strategies for iron-based superconductors.

Main Methods:

• Angle-resolved photoemission spectroscopy (ARPES).
• Local Density Approximation (LDA) calculations.
• Dynamical Mean Field Theory (DMFT) calculations.

Main Results:

• Electronic states near the Fermi level are a hybrid of Fe 3d and Ti 3d orbitals.
• A significant self-doping effect was observed, with 0.25 electrons/unit cell transferred from FeAs to Ti2As2O layers.
• The FeAs layer is found to be in a hole-doped state due to this electron transfer.
• Electronic correlations in 3d shells were identified as the cause of the self-doping effect.

Conclusions:

• The spacer layers in Ba2Ti2Fe2As4O contribute to its metallic nature.
• Self-doping, driven by electronic correlations, is a key feature of this superconductor.
• This study presents a new doping approach for iron-based superconductors without chemical substitution.