Orbital anisotropy of heavy fermion Ce$_{2}$IrIn$_{8}$ under crystalline electric field and its energy scale

TL;DR

This study explores how orbital anisotropy in Ce$_{2}$IrIn$_{8}$ evolves with temperature and influences spectral and optical properties, revealing a new temperature scale linked to crystalline electric field effects.

Contribution

It introduces a comprehensive analysis of orbital anisotropy's temperature dependence and its impact on spectral features, highlighting the role of CEF splitting in heavy fermion systems.

Findings

Orbital anisotropy develops as temperature decreases.

A spectroscopic shoulder appears at the Fermi level due to CEF excited state depopulation.

An additional temperature scale related to orbital anisotropy is proposed.

Abstract

We investigate the temperature ($T$)-evolution of orbital anisotropy and its effect on spectral function and optical conductivity in Ce$_{2}$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.