Shapiro Steps in I-V Curves of Josephson Point Contacts Made of Ba–Y–Cu–O Ceramics

Using BaYCuO ceramics having Tc(zero)=86K, point-contact Josephson devices have been fabricated. The devices were made of lead-ceramics and ceramics-ceramics point-contacts. X band radio frequency power was applied to the devices to measure rf induced voltage steps (Shapiro-steps) in I–V curves. Clear Shapiro-steps were observed at 4.2K in the lead-ceramics devices. By using the ceramics-ceramics devices Shapiro-steps were observed at 77K (in liquid nitrogen). The observed step-voltage V O and applied frequency f satisfied the relation V O =n(h/2e)f, where h and e are respectively, the Planck constant and electron charge and n is an integer.