Contact resistance characteristics of high temperature superconducting bulk. Part IV

The authors have measured contact resistances between two bulk YBCO superconductor blocks for the application to a persistent current switch (PCS). In order to reduce a contact resistance, we deposited indium and silver on the sample surfaces. The resistance was reduced by increasing the thickness of the deposited metal layers, but it saturated when the thickness reached a certain level. The saturation thickness was much smaller in indium than silver. Such a difference is understandable by considering the hardness of these two metals. The resistance was also reduced by increasing the mechanical load. Overloading however caused the adhesion of metal layers, resulting in the peeling off of the deposited layers when the switch was opened. Additionally, the contact area of the switch was analyzed with finite element method (FEM). This analysis result may lead to the elucidation of a contact mechanism with the contact surfaces deposited metal.