Orbital-differentiated coherence-incoherence crossover identified by   photoemission spectroscopy in LiFeAs
  In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/yz orbital yield quasi-particles with dxy} orbital character having larger mass renormalization and 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 quasi-particle (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. 
H. Miao, Z. P. Yin, S. F. Wu, J. M. Li, J. Ma, B. -Q. Lv, X. P. Wang,   T. Qian, P. Richard, L. -Y. Xing, X. -C. Wang, C. Q....
cond-mat.str-el cond-mat.supr-con