Speaker: Heike Pfau, Penn State University

Time: 10:00-11:00am

Location: BRIM 311

Abstract: Understanding how renormalized quasiparticles emerge in strongly correlated electron materials provides a challenge for both experiment and theory. It has been predicted that distinctive spin and orbital screening mechanisms drive this process in multiorbital materials with strong Coulomb and Hund’s interactions. In this talk I will focus on hole-doped iron-based superconductors AFe₂As₂ (A=Rb,Cs), which are the most correlated members of this material class with large effective masses and strongly renormalized band dispersions. It is currently debated which role electronic correlations play in the complex phase diagrams of iron-based materials, which contain unconventional superconducting, nematic, and magnetic phases as well as strange metal behavior.

In our angle-resolved photoemission spectroscopy (ARPES) study, we observe the existence of two screening processes. The emergence of low-energy Fe 3d_xy quasiparticles at low temperatures is tied to spin screening. A second process changes the spectral weight at high energies up to room temperature. Supported by material-specific and model calculations, we propose that orbital screening of Fe 3d atomic excitations is responsible for it. These two cascading screening processes drive the temperature evolution from a bad metal to a correlated Fermi liquid [1,2].

[1] M-H. Chang et al., Nature Comm. 15, 9958 (2024).

[2] M-H. Chang et al., Commun. Mater 6, 157 (2025).