The electrical properties of YBa2Cu3O7−δ thin films of various thicknesses grown upon MgO substrates

Abstract We have studied the vortex-related phase-transition-like behaviour in high quality YBa 2 Cu 3 O 7− δ (YBCO) films of thickness ranging from 10 to 200 nm grown upon MgO substrates using a DC inverted cylindrical magnetron sputtering (ICMS) technique. Good scaling collapse of the current–voltage isotherms from the region near the transition has been observed under an algorithm based on the hypothesis that there is a continuous thermodynamic phase transition such as the one proposed for the transition between a vortex-glass and a vortex-liquid. The scaling works for all film thicknesses, and from zero magnetic field through the fields of the order of 1 T. Even though we have not been able to explore the lower scaling branch of the 10 nm film at higher fields, it is noteworthy that the same algorithm, rather than the one proposed for 2D behaviour, collapses the data. For the 30–200 nm thick films, we observe systematic variation of the scaling exponents z and ν with film thickness and magnetic field; in particular, z increases substantially with decreasing film thickness. For the 10 nm film, the exponents found are similar to those of very thick films. We point out that the magnitudes of zν and the range of temperatures over which good scaling collapse is observed are not consistent with an interpretation based on a continuous thermodynamic phase transition, which clearly fails to capture some important elements of the physics.