2026-09-21T18:27:36Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/23925 2023-07-10 col_2142_8859 col_2142_5131 com_2142_8858 com_2142_234 com_2142_5130

Cooper, Stephen Lance Klein, Miles V. 2011-05-17T17:56:29Z 2011-05-17T17:56:29Z 10000-01-01 1988 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· Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-05-17T17:56:29Z No. of bitstreams: 1 1988_cooper.pdf: 13071942 bytes, checksum: 4f4b6229fc067031650087eed24c7553 (MD5) Made available in DSpace on 2011-05-17T17:56:29Z (GMT). No. of bitstreams: 1 1988_cooper.pdf: 13071942 bytes, checksum: 4f4b6229fc067031650087eed24c7553 (MD5) Previous issue date: 1988 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-05-17T17:56:29Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:15:57-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis Thesis U of I Only 1565937 http://hdl.handle.net/2142/23925 en 1988 Stephen Lance Cooper light scattering heavy fermion high Tc superconductors excitation spectra spin fluctuations crystal field excitations Light scattering studies of heavy fermion and high Tc superconductors Dissertation / Thesis text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.