Vortex-related phase-transition-like behavior in the electrical properties of c-axis normal and vicinal YBa2Cu3O7-Φ films

We examine the electrical transport behavior close to vortex "phase-transition-like" region in YBa 2 Cu 3 O 7 - Φ films that have their c axes tilted from the film plane normal by angles of 0°, 5°, 10°, and 15°. The I-V isotherms for all films collapse accurately under the vortex-glass scaling algorithm, for magnetic fields of 0.01-1 T applied at angles θ of 0° to 90° with respect to the c axis. The critical exponent v lies in the range 1.3-1.7 for all films, field strengths and field orientations. The critical exponent z is magnetic-field strength dependent in all films and for B∥c is considerably larger for the group of tilted films than for the 0° film. z varies with magnetic-field angle in an opposite sense in the 0° film and in the group of tilted films. The "transition" temperatures, T t (B,θ), are broadly described by the expression (T c -T t )/T t (e θ B) β , where e θ = [cos 2 (θ)+e 2 sin 2 (θ)] 1 / 2 and e=(m a b /m c ) 1 / 2 . However, β≅½, for the 0° film while β1 for the group of tilted films. Thus, we find that the tilted films have a number of common behaviors that are quite distinct from those of the 0° film, indicating a dependence of the "phase-transition-like" behavior on film structure. The high and variable values of z and the lack of "universality" between film types does not allow an interpretation of the accurate I-V collapses as being evidence for a continuous equilibrium phase transition such as one between a vortex liquid and a vortex glass and we consider models based on flux creep and inhomogenous pinning due to defects.