We report a comprehensive infrared magnetospectroscopy study of a CeRu4Sb1212 compound revealing quasiparticles with a heavy effective mass m*, with a detailed analysis of optical constants in fields up to 17 T. We find that the applied magnetic field strongly affects the low-energy excitations in the system. In particular, the magnitude of m*≃70 mb (mb is the quasiparticle band mass) at 10 K is suppressed by as much as 25% at 17 T. This effect is in quantitative agreement with the mean-field solution of the periodic Anderson model augmented with a Zeeman term.

@article{
  title = {Heavy Fermion Fluid in High Magnetic Fields: An Infrared Study of CeRu$_4$Sb$_{12}$},
  author = {Dordevic, S. V. and Beach, K. S. D. and Takeda, N. and Wang, Y. J. and Maple, M. B. and Basov, D. N.},
  journal = {Physical Review Letters},
  volume = {96},
  issue = {1},
  pages = {017403},
  numpages = {4},
  year = {2006},
  month = {Jan},
  publisher = {American Physical Society},
  doi = {10.1103/PhysRevLett.96.017403},
  url = {https://link.aps.org/doi/10.1103/PhysRevLett.96.017403}
}