Abstract
Strong correlations between the Hall coefficient , the transition temperature , and the critical current density were established in a series of epitaxial thin films as a function of oxygen deficiency δ. Steady increases in with δ suggest that deoxygenation reduces the density of states which, according to BCS theory, should lead to corresponding decreases in . In contrast, two well-known plateaus occurring at 90 K and 60 K were observed in vs δ. Others have ascribed these plateaus to either electronic phenomena or phase separations. We find that in the 90-K plateau, the critical current density (δ,H=0) decreases with δ and extrapolates toward zero at the edge of the plateau, while the relative-field dependence of (δ,H) and the flux-creep pinning energies are independent of δ. These observations suggest that the phase-separation scenario occurs on the 90-K plateau. However, electronic origins cannot be ruled out at present due to difficulties in determining the equilibrium superconducting properties of oxygen-deficient films.
- Received 18 December 1992
DOI:https://doi.org/10.1103/PhysRevB.47.8986
©1993 American Physical Society