CORRELATIONS BETWEEN THE HALL-COEFFICIENT AND THE SUPERCONDUCTING TRANSPORT-PROPERTIES OF OXYGEN-DEFICIENT YBA2CU3O7-DELTA EPITAXIAL THIN-FILMS

Strong correlations between the Hall coefficient R(H), the transition temperature T(c), and the critical current density J(c) were established in a series of epitaxial YBa2Cu3O7-delta thin films as a function of oxygen deficiency delta. Steady increases in R(H) with delta suggest that deoxygenation reduces the density of states which, according to BCS theory, should lead to corresponding decreases in T(c) . In contrast, two well-known plateaus occurring at 90 K and 60 K were observed in T(c) vs delta. Others have ascribed these plateaus to either electronic phenomena or phase separations. We find that in the 90-K plateau, the critical current density J(c) (delta, H = 0) decreases with 8 and extrapolates toward zero at the edge of the plateau, while the relative-field dependence of J(c)(delta,H) and the flux-creep pinning energies are independent of delta. 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 YBa2Cu3O7-delta films.