Infrared transmission and break-junction tunneling studies of the high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}
Infrared and tunneling spectroscopies are invaluable for the study of superconductivity because both techniques proved a sensitive low energy probe of the quasiparticle excitation spectrum. This dissertation deals with the application of these spectroscopies to ultra-thin (d {le} 1000{angstrom}) single crystals of the high temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. An account is given of the methods used to prepare these ultra-thin crystals, as well as the steps taken to ensure that the samples were of high quality. In this regard, the results of a number of different transport measurements are presented. An account is then given of an extensive experimental search for the energy gap performed using the far infrared radiation provided by beamline IR4 of the National Synchrotron Light Source. This search involved infrared transmission measurements on pure, yttrium doped, oxygen deficient, and electron-irradiated specimens of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. the frequency range of the measurements was extended, and a Kramers-Kronig analysis was performed to extract the optical conductivity of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. Neither in the transmission spectra nor in the optical conductivity could be feature be distinguished that could unambiguously be associated with a superconducting energy gap. Next an account is given of the break-junction tunneling experiments. Junctions with barriers both nominally perpendicular and parallel to the copper oxide planes were fabricated. These different configurations resulted in very different tunneling spectra. For c-axis tunneling, a significant zero bias conductance was observed at low temperature, and the conductance had a logarithmic voltage and temperature dependence. The ab-plane conductance approached zero at zero bias and followed G(V) {approximately} V{sup 2} at low bias, peaking at 55mV. the ab-plane tunneling data were deconvolved to extract an effective density of states (DOS).
- Research Organization:
- State Univ. of New York, Stony Brook, NY (United States)
- OSTI ID:
- 114802
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1992
- Country of Publication:
- United States
- Language:
- English
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