Probing the hybridization gap in heavy fermions by temperature dependent ARPES

We report temperature dependent angle-resolved photoemission spectroscopy (ARPES) for pure and Cd-doped Ce$_{2}$RhIn$_{8}$ heavy fermion compounds. Our results reveal that for Ce$_{2}$RhIn$_{8}$ at T $=$ 100 K once the $f $-- conduction electrons magnetic scattering becomes larger than the phonon scattering, even states of different parities can hybridize, forming many-body quasiparticles with heavy masses. We further show that at a temperature of 20 K, where the hybridization of conduction electrons and $f $states is stronger, a spectral gap is observable in the ARPES spectra. Interestingly, when replacing In by Cd to tune the local density of conduction electrons states at the Ce$^{3+}$ site, we find a strong reduction of the $f$ - conduction electrons hybridization strength, and the suppression of the hybridization gap at low temperatures. We also observe that the $f $states near the chemical potential hybridize mostly with out-of-plane $p$ states (presumably from In). These findings have important consequences for the understanding of the different antiferromagnetic and exotic superconducting ground states that occur in these families of materials.