We investigate the temperature $\left(T\right)$ evolution of orbital anisotropy and its effect on spectral function and optical conductivity in ${\mathrm{Ce}}_2{\mathrm{IrIn}}_8$ 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 $T_K$ and $T^{*}$, we introduce an additional temperature scale to deal with the orbital anisotropy in heavy fermion systems.

• Received 24 January 2021
• Revised 18 January 2022
• Accepted 23 March 2022

DOI:https://doi.org/10.1103/PhysRevB.105.115147