GHz Irradiation Research Articles

Observation of the AC Josephson effect up to THz frequencies in YBCO/PBCO/YBCO ramp-type Josephson junctions

We present the response to 100 GHz irradiation of high- T c Josephson junction devices for mixer/detector applications in the (sub-) mm wave range. These devices consist of a YBCO/PBCO/YBCO ramp-type junction combined with a planar logarithmic periodic antenna. The critical current and the first two Shapiro steps modulate with 100 GHz power according to the resistively shunted junction (RSJ) model. At 10 K clear Shapiro steps have been observed up to a voltage of about 7.5 mV. This corresponds to phase locking of 3.6 THz AC Josephson oscillations by the 36th harmonic of the 100 GHz signal. The number of observed steps is currently limited by the available power, but they are present up to voltages strongly exceeding the I c R n product of the junction at all temperatures.

Observation of a devil's staircase on a GdMo 6Se 8 Josephson junction

We present the first observation of a devil's staircase on a microwave irradiated Josephson junction. A crack type junction prepared from the bulk polycrystalline magnetic superconductor GdMo 6Se 8 was used. The observations were done at a temperature of 1.3 K under 9.5 GHz irradiation. The results confirm the presence of a quasiperiodic route to chaos in real Josephson junctions predicted by former analog and digital simulations.