Continuity of Ce 4f electronic structure across the quantum critical point: A resonant photoemission study on CeNi1-xCoxGe2

Ce 3d-4f and 4d-4f resonant photoemission spectroscopies have been performed on the heavy-fermion compound CeNi1-xCoxGe2, where the ground-state properties systematically change from the magnetic (0≤x<0.3) to nonmagnetic (0.3<x≤1.0) regime via the quantum critical point (QCP, x=0.3). Co-substitution dependence of the bulk Ce 4f electronic structure shows gradual evolution of Kondo resonance at the Fermi level together with the reduction of the Ce 4f0 final state in agreement with the single impurity Anderson model (SIAM). The SIAM analysis shows that the Kondo temperature and specific-heat coefficient change continuously from the weakly hybridized CeNiGe2 to strongly hybridized CeCoGe2. These indicate that the Ce 4f electronic structure of CeNi1-xCoxGe2 changes continuously through the QCP.