Intrinsic AC Shunting in [100]-Tilt Bicrystal YBa2Cu3O $_{7 - x}$ Josephson Junctions

[100]-tilt YBa2Cu3O7-x bicrystal Josephson junctions are good candidates to realize high values of characteristic voltages IcRn, which are expected due to large energy gaps in high-Tc materials. Here, we report on detailed electrical characterization of [100]-tilt YBa2Cu3O7-x bicrystal Josephson junctions, which have the maximal IcRn-values up to 9.4 mV, for resistances Rn in the range from 0.9 to 400Ω. The I-V curves have been fitted well to those of the RSJ model with ac-coupled resistive shunts Re. The first derivatives dV/dI versus V have demonstrated a reproducible set of resonances of two types. Numerical simulations of the dV/dI versus V for Josephson junctions coupled with external THz RLC-resonators have been made and both types of resonances have been fitted. A form of the I-V curves and resonances in the first derivatives dV/dI versus V have been attributed to intrinsic broadband and frequency-selective losses, due to interaction of Josephson oscillations with transverse and longitudinal IR-active phonons in YBa2Cu3O7-x electrodes