Description
We report an angle-resolved photoemission spectroscopy study of superconducting Sm$_{0.75}$Eu$_{0.2}$Ca$_{0.05}$NiO$_2$, a high-$T_c$ infinite-layer nickelate with high crystalline quality. The measured low-energy electronic structure consists of a large hole-like $\alpha$ band and a small electron-like $\beta$ pocket near the Brillouin-zone corner. Contrary to expectations based on a possible Lifshitz transition, the $\alpha$ band remains electron-like in the saddle-point region and does not undergo a topology change. Polarization-dependent measurements identify the $\alpha$ pocket as predominantly Ni $d_{x^2-y^2}$ in character, while the $\beta$ pocket is consistent with an interstitial-$s$-derived state. Compared with La$_{0.8}$Ca$_{0.2}$NiO$_2$, Sm$_{0.75}$Eu$_{0.2}$Ca$_{0.05}$NiO$_2$ exhibits a more three-dimensional $\alpha$ pocket and a slightly larger $\beta$ pocket volume, highlighting the evolution of three-dimensional electronic states across the infinite-layer nickelates.
