Fig. 6: Cascade of screening processes.
From: Observation of two cascading screening processes in an iron-based superconductor
A comparison of the resistivity R (from ref. 33), the magnetic susceptibility χm (from ref. 28) and the quasiparticle spectral weight change ΔI of the dxy and dxz orbitals (from Figs. 2d and 3i). Top: Sketches illustrate orbital and spin screening in the example of three atomic orbitals (circular segments) occupied by two electrons (adapted from ref. 71). Right: Hund’s rule coupling favors a parallel spin alignment of both electrons in the atomic orbitals. Center: Orbital screening (second circle) of the atomic configuration leads to an orbital singlet. Hund’s rule coupling favors the large spin state. Left: Spin screening (third circle) of the large moment then leads to the formation of a spin singlet. The Fermi liquid regime has a constant χm and a T2 dependence of R. Spin screening is identified as the crossover between Pauli and Curie behavior in χm. It coincides with a crossover in the resistivity (slope change). The dxy quasiparticle emerges once spin screening sets in. Orbital screening leads to a spectral weight transfer from the Hubbard bands to the dxz quasiparticle peak. Its intensity increases over the whole screening temperature range.
