Date of Award

1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Roy G. Goodrich

Abstract

Magnetization and de Haas - van Alphen (dHvA) measurements have been made on the high temperature superconductor Ba$\sb{0.6}$K$\sb{0.4}$BiO$\sb3$ and the heavy fermion CeB$\sb6$. First ever observations of the dHvA effect in Ba$\sb{0.6}$K$\sb{0.4}$BiO$\sb3$ are reported. Two dHvA spectrometers (pulsed field and field modulation) were used to measure two samples. Four frequencies are found in the field modulation data with the 11.6 kT orbit in good agreement with band structure calculations. The three lowest frequencies were measured with the pulsed field spectrometer. All dHvA measurements were made in the superconducting mixed state. These measurements indicate that Ba$\sb{0.6}$K$\sb{0.4}$BiO$\sb3$ has a Fermi surface. Magnetization measurements on Ba$\sb{0.6}$K$\sb{0.4}$BiO$\sb3$ suggest a superconducting to normal state phase transition of an order greater than two given that both the specific heat and susceptibility discontinuities across T$\sb{c}$ and H$\sb{c2}$ are zero. All thermodynamic critical fields exhibit a positive curvature as the temperature approaches zero. The present measurements suggest that the value of H$\sb{c2}$(T = 0) is higher than previously thought with the possibility that it diverges at zero temperature. Measurements on CeB$\sb6$ at temperatures as low as 25 mK and in fields as high has 50 T reveal that the dHvA frequency of the belly orbit in the (100) direction changes as a function of field, decreasing in frequency with increasing applied field. This is evidence that the Fermi surface of CeB$\sb6$ is polarized. Fermi surface polarization together with the observed magnetic field dependence of the cyclotron mass adequately account for the measured frequency shift. Additionally, the observed frequency shift can be modeled with a form of the Lifshitz-Kosevich equation modified to allow for the effects of strong correlations.

ISBN

9780591723885

Pages

267

DOI

10.31390/gradschool_disstheses.6568

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