Fermi surface variation of Ce 4f-electrons in hybridization controlled heavy-fermion systems

•Fermi surface topology of CeCoGe1.2Si0.8 and CeCoSi2 has been investigated by Ce 3d–4f resonant ARPES.•The ARPES results reveal the evolution of Ce 4f Fermi surface with the c-f hybridization strength.•The strong correlation effects influence on Ce 4f Fermi surface topology.

Ce 3d–4f   resonant angle-resolved photoemission measurements on CeCoGe1.2Si0.8CeCoGe1.2Si0.8 and CeCoSi2 have been performed to understand the Fermi surface topology as a function of hybridization strength between Ce 4f- and conduction electrons in heavy-fermion systems. We directly observe that the hole-like Ce 4f-Fermi surfaces of CeCoSi2 is smaller than that of CeCoGe1.2Si0.8CeCoGe1.2Si0.8, indicating the evolution of the Ce 4f-Fermi surface with the increase of the hybridization strength. In comparison with LDA calculation, the Fermi surface variation cannot be understood even though the overall electronic structure is roughly explained, indicating the importance of strong correlation effects.