Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs

Abstract

In iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the ${d}_{xy}$ orbital than on the ${d}_{xz}/{d}_{yz}$ orbital yield quasiparticles with a ${d}_{xy}$ orbital character having larger mass renormalization and an abnormal temperature evolution. However, the physical origin of this orbital differentiation is debated between the Hund's coupling-induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital-selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasiparticle (QP) anomaly in LiFeAs. The excellent agreement between our photoemission measurements and first-principles many-body theory calculations shows that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.