Field-dependent resistive transitions in Yba₂Cu₃O_7-δ thin films: Influence of the pseudogap on vortex dynamics

The nature of resistive transition of high-quality crystalline thin films of Yba₂Cu₃O_7-δ has been studied under magnetic fields (H) applied along the c direction over a wide range of doped holes, p, in the CuO₂ planes. The field- and temperature-dependent in-plane resistivity, ρ_ab(T,H), has been analyzed within the thermally assisted flux-flow (TAFF) formalism. The flux activation energy, U(T,H), has been extracted from this analysis. The low-T part of the ρ_ab(T,H) data can be described by an activation energy having the functional form of U(T,H) = (1-t)^m(H₀/H)^-β, where t = T/T_c (reduced temperature), and H₀ is a field scale that primarily determines the magnitude of U(T,H). The temperature exponent, m, shows a systematic variation with p, whereas the field exponent, β, is insensitive to the p values and is close to unity. The H₀, on the other hand, changes rapidly as p is varied. U(T,H) is linked to the pinning potential and consequently on the superconducting condensation energy. Since the normal state pseudogap directly affects superconducting condensation energy, a clear correspondence between H₀ and the PG energy scale, ε_g, is found. Possible implications of these results are discussed.