Synchronization in stacked array of the Josephson junctions in Bi₂Sr₂CaCu₂O_8+δ

Intrinsic stacked array of Josephson junctions will find potential application as voltage standard or HTSC Josephson spectral detector if internal Josephson oscillations in different layers can be synchronized under electromagnetic radiation. In our experiments we studied synchronization is stacked array of Josephson oscillations contained up to 2500 junctions in Bi₂Sr₂CaCu₂O_8+δ. Phase locking of the internal Josephson oscillation in array to externally applied microwave radiation was manifested by observation of the collective Shapiro steps. Synchronization of all junctions in array was possible in the vortex glass state in high magnetic fields and vortex liquid state on the B-Tc-axis vortex phase diagram in frequency range 80-140 GHz. In those regions damping is significantly enhanced and hysteresis on I-V characteristics collapsed. Observations deny major opinion that intrinsic Josephson junctions in Bi₂Sr₂CaCu₂O_8+δ are always underdamped. We interpret our results as a reflecting the pancake vortex disorder and fluctuations in CuO₂ layers