Light scattering studies of heavy fermion and high Tc superconductors

In this thesis, light scattering techniques are used to probe the diverse excitation spectra of heavy fermion and high T c superconductors. Our studies of heavy fermion compounds principally demonstrate the efficacy of using light scattering techniques to probe spin fluctuations and crystal field excitations in metals. For example, light scattering from spin fluctuations in UBe13, UPt3, and URu2Si2 reveals a substantial q=O contribution to the magnetic susceptibility in these compounds. This result demonstrates that a spin-conserving Fermi liquid description of heavy fermion compounds is invalid. Furthermore, the q=O spin relaxation rates we observe in several heavy fermion superconductors differ markedly from those observed in highu-q neutron scattering data, suggesting that intersite magnetic correlations are present in these materials. Additionally, crystal field excitations are evident in CeCu2Si2, and are found to exhibit damping effects which are consistent with theoretical predictions. Finally, an investigation of the phonon spectra of several heavy fermion compounds presents evidence for anomalous magnetoelastic and deformation potential coupling in some heavy fermion compounds. Polarized light scattering studies of YBa2Cu307-5 reveal strong interband electronic scattering which interferes strongly with certain phonons. These interference effects indicate t_he presence of strong electron-phonon coupling in this compound. Below Tc, the electronic continuum exhibits both a loss of spectral weight at low energies, and a broad peak at high energies due to the direct excitation of superconducting quasiparticle pairs above the gap. The observed anisotropy in the Raman matrix elements associated with these superconducting gap excitations lV presents strong evidence for substantial gap anisotropy in YBa2Cu301-B· However, our lowest temperature data also demonstrates the presence of residual electronic scattering well below the expected 2.!\ quasiparticle pair-breaking energy. This result suggests that a continuum of electronic states exists well inside the superconducting gap. The transition to the superconducting state is also reflected in a Raman active phonon which demonstrates interesting quasiparticle self-energy effects below T c·

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Cooper, Stephen Lance

Contributors dc:contributor

• Klein, Miles V.

• light scattering
• heavy fermion
• high Tc superconductors
• excitation spectra
• spin fluctuations
• crystal field excitations

Statement dc:rights

• 1988 Stephen Lance Cooper

Language dc:language

en

Identifier

1565937

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/23925