Investigations of the in-plane anisotropy and the critical behaviour of 10degrees-tilted YBa2Cu3O7-delta films grown upon (106) SrTiO3 substrates

We describe the electrical properties of 10 degrees-tilted YBa2Cu3O7-delta (YBCO) films grown epitaxially upon as-received (106) SrTiO3 substrates. (1 06) substrates which have been annealed at sufficiently high temperatures m ay exhibit a regular "step-and-terrace" surface structure, while un-anneale d substrates (UAS) have more irregular terracing. We show that both the nor mal state and the superconducting properties of films grown upon UAS films vary considerably from the reported properties of films grown upon annealed substrates (AS films). The normal state in-plane anisotropies of UAS films are close to that of a near-perfect single crystal, while the in-plane ani sotropy falls smoothly towards unity as the temperature is lowered through the superconducting regime. The critical currents of UAS films are lower th an those of AS films. The superconducting behaviour of UAS films is consist ent with a reduced density of extended defects including anti-phase boundar ies, defects to which many of the properties of AS films have been attribut ed. We have also studied the properties of the phase-transition-like electr ical behaviour found in UAS films, and observed good scaling collapse of th e data under an algorithm based on a continuous thermodynamic phase transit ion such as that between a vortex liquid and a vortex glass. We find that t he transition temperature, T-t, and the scaling exponents v and z do not de pend upon the direction of the measurement current, but that the scaling is not "universal" since the exponents depend upon magnetic field and upon fi lm thickness. The values of the exponents are far higher than might be expe cted from a continuous thermodynamic phase transition. The scaling of data for the track of a film which has been etched shows that both the exponents and the scaling functions are strongly influenced by chemical treatment. ( C) 1999 Elsevier Science B.V. All rights reserved.