Hysteresis of the current-voltage characteristics and electric field effects in bulk YBCO superconductors

Some YBCO ceramics have been found to exhibit hysteresis of the current/voltage, I/V, characteristics, which reveals at a certain current I_f greater than critical current I_c a transition with switch from one branch of the I/V curve to another. In present work, the influence of an electric field at 77 K on hysteresis of I/V curves of ceramic YBCO/Ag and YBCO after hydrogen treatment has been studied. It was established that in strong electric field (120 MV/m) the conductivity increases at current I>I_c, the field effect being observed only in the upper branch of hysteresis loop. The electric field effect in YBCO after hydrogen treatment is reversible. The observed effects are assumed to be associated with a change of grain boundary weak links from S/I/S-to S/N/S-type in the course of hydrogen treatment or addition of silver into ceramics.