Orbital anisotropy of heavy fermion Ce2IrIn8 under crystalline electric field and its energy scale

We investigate the temperature (T ) evolution of orbital anisotropy and its effect on spectral function and optical conductivity in Ce2IrIn8 using a first-principles dynamical mean-field theory combined with density functional theory. The orbital anisotropy develops by lowering T and it is intensified below a temperature corresponding to the crystalline-electric field (CEF) splitting size. Interestingly, the depopulation of CEF excited states leaves a spectroscopic signature, ???shoulder,??? in the T-dependent spectral function at the Fermi level. From the two-orbital Anderson impurity model, we demonstrate that CEF splitting size is the key ingredient influencing the emergence and the position of the ???shoulder.??? Besides the two conventional temperature scales TK and T *, we introduce an additional temperature scale to deal with the orbital anisotropy in heavy fermion systems.