Rf-induced dc voltages across unbiased terminals and current-voltage characteristics of microwave-driven high-Tc SQUIDs

Quantized voltage across the unbiased terminals of a bicrystal YBa2Cu3O7 dc SQUID exposed to microwave radiation has been observed at 77 K. Using this voltage as an indication of the microwave power coupled to the junctions, we identified three distinct regions in the I-V curves as the microwave power was tuned, similar to those reported for low-Tc SQUID. Pronounced double period steps were observed when the microwave radiation power was high enough to suppress the dc Josephson current completely. Half-integer steps also appeared as the applied dc-magnetic flux was close to half-integers of flux quanta. The experimental phenomenon was explained based on the resistively shunted Josephson junction model. (author)