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

Abstract We describe the electrical properties of 10°-tilted YBa 2 Cu 3 O 7− δ (YBCO) films grown epitaxially upon as-received (106) SrTiO 3 substrates. (106) substrates which have been annealed at sufficiently high temperatures may exhibit a regular “step-and-terrace” surface structure, while un-annealed substrates (UAS) have more irregular terracing. We show that both the normal 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 anisotropy falls smoothly towards unity as the temperature is lowered through the superconducting regime. The critical currents of UAS films are lower than those of AS films. The superconducting behaviour of UAS films is consistent with a reduced density of extended defects including anti-phase boundaries, defects to which many of the properties of AS films have been attributed. We have also studied the properties of the phase-transition-like electrical behaviour found in UAS films, and observed good scaling collapse of the data under an algorithm based on a continuous thermodynamic phase transition such as that between a vortex liquid and a vortex glass. We find that the transition temperature, T t , and the scaling exponents ν and z do not depend upon the direction of the measurement current, but that the scaling is not “universal” since the exponents depend upon magnetic field and upon film thickness. The values of the exponents are far higher than might be expected 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.