Fermi Surface evolution as a function of temperature in heavy fermion Ce$_{2}$RhIn$_{8}$ probed by ARPES

The crossover of 4$f$ localized magnetic moments at high temperatures into itinerant states of heavy mass at low temperatures in Cerium-based heavy fermion materials is a fundamental problem in condensed matter physics, involving a temperature-dependent hybridization between the $f$ levels immersed in a sea of conduction electrons (\textit{ce}). Due to the Luttinger theorem, this hybridization leads to a Fermi surface (FS) enlargement at low temperature: as the $f$ electrons become itinerant, their contribution to E$_{\mathrm{F}}$ increases. We have studied the evolution of the heavy fermion FS in Ce2RhIn8 as a function of temperature using angle resolved photoemission. We observed topological changes that emerge at a temperature scale much higher than the onset of the coherence character of the $f$ electrons. This behavior can be related to the evolution of the electrical resistivity as a function of temperature: as typically found for Kondo lattice materials, it first decreases when temperature is lowered, but increases below $\sim $ 150K as the magnetic scattering of the \textit{ce} by the localized $f$ electrons becomes larger than the phonon scattering. It reaches a maximum and then drops when the magnetic scattering becomes coherent for T$^{\ast} \sim $ 5K. This multiple scale behavior of the $f$ electrons is in good agreement with a recent theoretical study performed in the parent compound CeRhIn$_{5}$ [1].\\[4pt] [1] Choi et al, Phys. Rev. Lett. \textbf{108}, 016402.