Thermal effect of contacts on the current-voltage characteristics of high Tc YBa2Cu3Ox superconductor films

The effect of contact-generated heat on the current-voltage characteristics of thin superconducting films is examined. The generation of heat at the contact creates a transient normal zone adjacent to the interface that propagates into the film and causes the electrical characteristics to be nonlinear and time-dependent. A transient one-dimensional fin-type heat equation is utilized to predict the temperature field, which is evaluated by a finite difference scheme. Specific cases of YBa₂Cu₃O_x films connected via indium leads are considered. Two parameters of importance are introduced: transition time and transition current. The transition time is defined as the time elapsed before a normal zone is created in the superconducting film and the transition current density is the current density that must be reached before a normal zone is created. These parameters are evaluated for three different types of current pulses and for different operating temperatures