Correlations and Screening in the Iron-based superconductor RbFe2As2

The electronic structure of iron-based superconductors is characterized by an interplay of Coulomb interaction and Hund’s rule coupling acting on a multiband system. It is currently debated which role electronic correlations play in the complex phase diagrams that contain unconventional superconducting, nematic, and magnetic phases as well as strange metal behavior. Electronic correlation effects are particularly pronounced in the hole-doped AFe₂As₂ (A=K,Rb,Cs), which show large effective masses and strongly renormalized band dispersions.

Here, we present a comprehensive overview on how electronic correlations affect the spectral function of RbFe2As2 using a combination of angle-resolved photoemission spectroscopy (ARPES) and dynamical mean field theory (DMFT). We will discuss how atomic excitations of the localized Fe 3d shell are screened at low temperature, which leads to the emergence of long-lived, heavily renormalized quasiparticles. This process is a hallmark of strongly correlated electron systems and connects iron-based superconductors to systems like heavy fermions, cuprates and nickelates. The quasiparticle dispersion develops two strong kinks that originate from electronic interactions. The low-energy kink is likely caused by a coupling to spin excitations, which suggests their involvement in the formation of unconventional superconductivity in RbFe₂As₂.