Correlations between the Hall coefficient and the superconducting transport properties of oxygen-deficient ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ epitaxial thin films

Strong correlations between the Hall coefficient ${\mathit{R}}_{\mathit{H}}$, the transition temperature ${\mathit{T}}_{\mathit{c}}$, and the critical current density ${\mathit{J}}_{\mathit{c}}$ were established in a series of epitaxial ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ thin films as a function of oxygen deficiency δ. Steady increases in ${\mathit{R}}_{\mathit{H}}$ with δ suggest that deoxygenation reduces the density of states which, according to BCS theory, should lead to corresponding decreases in ${\mathit{T}}_{\mathit{c}}$. In contrast, two well-known plateaus occurring at 90 K and 60 K were observed in ${\mathit{T}}_{\mathit{c}}$ 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 ${\mathit{J}}_{\mathit{c}}$(δ,H=0) decreases with δ and extrapolates toward zero at the edge of the plateau, while the relative-field dependence of ${\mathit{J}}_{\mathit{c}}$(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 ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ films.