Orbital-dependent electron dynamics in Fe-pnictide superconductors

Abstract

We report on orbital-dependent quasiparticle dynamics in EuFe${}_2$As${}_2$, a parent compound of Fe-based superconductors and a novel way to experimentally identify this behavior, using time- and angle-resolved photoelectron spectroscopy across the spin density wave transition. We observe two different relaxation time scales for photo-excited d${}_x$${}_z$/d${}_y$${}_z$ and d${}_x$${}_y$ electrons. While d${}_x$${}_z$/d${}_y$${}_z$ electrons relax faster through the electron-electron scattering channel, showing an itinerant character, d${}_x$${}_y$ electrons form a quasi-equilibrium state with the lattice due to their localized character, and the state decays slowly. Our findings suggest that electron correlation in Fe-pnictides is an important property, which should be taken into careful account when describing the electronic properties of both parent and electron-doped compounds, and therefore establish a strong connection with cuprates.