Investigation of the electrical dissipation properties of in-plane alignedalpha-axis YBCO films grown on (100) LaSrGaO4 substrates

a-axis YBa2Cu3O7-delta (YBCO) films have been grown on tetragonal (100) LaS rGaO4 (LSGO) substrates over a PrBa2Cu3O7-delta (PBCO) template layer, usin g inverted cylindrical magnetron (ICM) sputtering. Detailed X-ray diffracti on studies showed that more than 98% of the grains are in-plane aligned wit h the substrate axes. We have studied the vortex-related phase-transition-l ike behaviour in these films from dc electrical measurements made with the transport current along the b- and c-axes, and in magnetic fields up to 1 T . Good scaling collapse of the current-voltage isotherms for a wide range o f temperatures about the transition is observed when using an algorithm bas ed upon a continuous thermodynamic phase transition such as that between a vortex-liquid and a vortex-glass. We note that the critical scaling exponen ts are by no means "universal" as expected by some authors and that the exp onent z is far higher than expected from analogies with spin-glass systems. The wide range of temperature over which collapse occurs and the very high values of z make the usual association of z and z nu with a length and a t ime scale implausible. Importantly, the observed "transition" temperature, T-t, differs appreciably between the two transport current directions for t he same magnetic field and field angle. These observations cast doubt on an interpretation for the vortex-related behaviour based on a continuous ther modynamic phase transition such as that between a vortex-liquid and a vorte x-glass and alternative possibilities must be explored. (C) 2000 Elsevier S cience B.V. All rights reserved.