Probing the Superconducting Gap of Lead With Ballistic Phonons

123 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.The assumption that quasiparticles are all in thermal equilibrium with the helium-bath leads to erroneous results for temperature dependences of phonon absorption. Instead, we assume that the phonon-imaging experiment creates small regions of raised temperature that contribute non-equilibrium quasiparticles to the system. Accounting for these quasiparticles, we extract consistent values of both the superconducting energy gap parameter and the superconducting phonon absorption coefficient for all phonon-imaging data. Measured values of the energy gap (Delta = 1.32+/-0.07 meV)are consistent with accepted values from tunneling measurements. Phonon imaging experiments do not support the existence of an SDW ground state in Pb.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD