We report measurements of the Eg optical phonon in V3Ge, V3Si, and Nb3Sb, and of the T2g optical phonon in Nb3Sb measured from 9 to 400 K. The Eg optical phonon in V3Ge has an anomalous width, shape, and temperature dependence, similar to that seen in V3Si and Nb3Sn. Both the Eg and T2g optical phonons in Nb3Sb, on the other hand, show no anomalous behavior and can be understood in terms of simple anharmonic interactions. We point out the existence of a linear correlation between the magnetic susceptibility and the Eg phonon linewidth for V3Si, V3Ge, and Nb3Sn. Scaling arguments show that the Eg phonon linewidth of these three compounds exhibits very similar temperature dependences, with the remaining small differences yielding information concerning the distribution of the joint electronic density of states with respect to the Fermi level. These anomalies are attributed to coupling of the Eg phonon to interband electronic transitions between the flat bands emanating from the 12 level. A simple model of the interaction quantitatively reproduces the temperature dependence of the Eg phonon linewidth. © 1983 The American Physical Society.

The results of a Raman scattering study of single-crystal UBe13 are presented and discussed. These results are compared with spectra from the isostructural compounds MBe13 (M=La, Ce, Th), within the temperature range 3T350 K. Ten phonons are observed in UBe13, displaying symmetries 2A1g+4Eg+4T2g, consistent with predictions using the space- and site-group symmetries previously determined for this compound [space group Oh6 (Fm3c)]. In addition, electronic scattering is evident in our spectra, exhibiting the symmetry of the purely antisymmetric representation, T1g. Evidence suggests that this scattering results from localized excitations of the 5f electrons. Various interpretations of this scattering are discussed. © 1987 The American Physical Society.

The vibrational and crystal-field excitation spectrum is examined in CeCu2Si2 using polarized Raman scattering. These results are compared to spectra from the isostructural compounds RCu2Si2 (R=La,Gd,Yb) in the temperature range 2T390 K. The observed vibrational spectrum of CeCu2Si2 consists partly of a B1g and an A1g mode involving only Cu and Si atoms, respectively. Two Eg modes, involving both Cu and Si atoms, are also seen. An additional A1g phonon peak is observed, in defiance of the phonon spectrum allowed by the space-group symmetry of CeCu2Si2. This peak is believed due to disorder and is attributed to an A1g breathing mode of Cu atoms sitting at Si sites. Electronic crystal-field excitations are also evident in our spectra, displaying a broad peak centered roughly at 290 cm-1. This excitation is observed only in the purely antisymmetric A2g (depolarized) spectrum, and is seen to narrow and intensify with decreasing temperature. No other crystal-field transition is observed. The temperature dependence of the crystal-field excitation linewidth is discussed. © 1986 The American Physical Society.

Raman-scattering measurements on Nb3Sn and V3Si show new peaks in the superconducting state close in energy to the superconducting gap 2". These are attributed to direct electronic Raman scattering by pairs of superconducting quasiparticles. A theory is presented which fits the data well and provides evidence for anisotropy of the gap (20% in Nb3Sn) and of the matrix element for electronic Raman scattering. © 1983 The American Physical Society.

We have performed polarized Raman scattering experiments on single-crystal samples of UPt3 in the temperature range 5 KT340 K. Four of the five Raman-allowed phonons have been observed, and their symmetries identified. None of these phonons is seen to demonstrate any anomalous behavior, contrary to previous Raman scattering results. Additionally, quasielastic scattering from spin fluctuations has been observed, having the symmetry of the antisymmetric representation, A2g, and displaying a slightly temperature-dependent half width at half maximum. The energy scale of this scattering is consistent with results reported earlier by both neutron scattering at q1 A-1 and Raman scattering at q=0 (where q, is the momentum transfer) suggesting that the spin-fluctuation relaxation is q-independent. © 1988 The American Physical Society.

Raman scattering experiments on single-crystal UBe13 have been performed at temperatures 2≤T≤300 K. We observe Raman-active optical phonos consistent, in number and symmetry, with those allowed by the space and site group symmetries previously determined for UBe13 (space group O6hFm3c). Certain phonon modes are seen to have strongly anomalous behaviour with decreasing temperature. We have, in addition, observed inelastic scattering from magnetic excitations, which we identify as spin fluctuations. The temperature dependence of these excitations is discussed. © 1985.

Polarized light scattering measurements of some heavy fermion superconductors are presented and discussed. Light scattering affords a unique opportunity to study both the f electrons, which are thought to participate in the formation of the superconducting state, and the lattice excitations, which can demonstrate strong electron-phonon interactions and elastic anomalies in these compounds. These points are illustrated by presenting the results of light scattering experiments on single crystal samples of CeCu2Si2, UBe13, UPt3, and URu2Si2. © 1987.