Absence of Kondo effect in CeNiGe3 revealed by coherent phonon dynamics

Cerium-based intermetallic CeNiGe3 has been generally believed to be a heavy-fermion material with Kondo behavior at low temperatures. Using femtosecond-resolved coherent phonon spectroscopy, we present a temperature-dependent dynamic investigation of the bosonic quasiparticles in CeNiGe3. Our data do not agree with the heavy-fermion expectation and instead show that the phonon stiffening from room temperature down to 5 K can be well explained by the anharmonic effect in the absence of a Kondo mechanism. Furthermore, the coherent lattice vibration located at similar to 7.9 THz exhibits a mode splitting at T+ approximate to 105 K, which is close to the energy scale of the first excited crystal field splitting of the Ce 4 f level. We argue that an orbital crossover may account for this intriguing observation.