Raman and Brillouin Scattering Spectroscopy of Intermediate Valence and Heavy Fermion Compounds

Starting about ten years ago, Raman scattering has been used quite extensively to study the electron-phonon interaction and intraionic 4f multiplet excitations in intermediate valence compounds, mainly of the rare earth chalcogenides /1/. Over the past five years Raman and Brillouin scattering spectroscopies have increasingly been applied to investigate rare earth and actinide intermetallics, which exhibit valence instabilities and heavy fermion (HF) behavior. Both these high resolution, q ≈ O techniques have provided information complementary to neutron scattering investigations. Among the highlights are the study of crystalline-electric-field (CEF) excitations and their interaction with optical phonons in Kondo-like compounds /2/, the observation of intraionic and interconfigurational excitations in intermediate valence (IV) compounds, and the direct spectroscopic identification of the temperature dependence of the fluctuation temperature and the interconfigurational excitation energy /3,4/. Most recent achievements concern the experimental identification of the charge relaxation rates in IV compounds by phonon spectroscopy /5/ and the observation of anomalous electron-phonon coupling of a Raman-active (q ≈ 0) phonon in UPt3 /6,7/, similar to findings in A15 superconductors /8/. Quasielastic scattering due to spin fluctuations could be observed in UPt3 /6,7/ and UBe13 /9,10/. The theoretically predicted diffusive mode due to electron density fluctuations in heavy fermion systems /11/ has been found very recently by Brillouin scattering /12/.