The revival of Fe-based superconductors: cascades of screening processes and their implications
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 that 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 3dxy 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).
Bio: Heike Pfau is an assistant professor of physics at The Pennsylvania State University. She received her Ph.D. in physics from the Technical University Dresden & Max-Planck Institute CPfS in Dresden, Germany in 2015. Prior to that, she earned her Diploma Physics from the Technical University Dresden in 2010.
Pfau’s research focuses on materials with strong electronic correlations. These materials develop novel phenomena and unconventional electronic phases such as heavy fermion behavior, unconventional superconductivity, nematicity, and quantum criticality. She wants to advance the knowledge of such emergent collective phenomena using angle-resolved photoemission spectroscopy (ARPES) as well as low temperature transport and thermodynamic probes. Her main focus lies on correlated materials containing transition metal or rare-earth elements such as heavy fermion systems and iron-based superconductors.