Spectral range of the ac Josephson effect in [001]-tilt YBa/sub 2/Cu/sub 3/O/sub 7-x/ bicrystal junctions

We have studied the ac Josephson effect in YBa/sub 2/Cu/sub 3/O/sub 7-x/ bicrystal junction by monitoring the voltage dependence of the dc current response /spl Delta/I(V) induced by low-power monochromatic radiation with the frequencies f/sub i/. The intensity of odd-symmetric resonances in the function /spl Delta/I(V) near the voltages V/sub i/=hf/sub i//2e is proportional to the amplitude of Josephson oscillations at the frequency f/sub i/. The resonance intensities have been mapped as a function of the Josephson frequency f/sub i/ in the range from 5 GHz to 5 THz, the junction resistance R/sub n/ in the range from 0.4 to 80 Ohm and junction characteristic voltages I/sub c/R/sub n/ in the range from 5 /spl mu/V to 1.8 mV. The central frequency of the range was scaled with the I/sub c/R/sub n/-product of the junction and it could be shifted from GHz-range to the THz-range by a temperature decrease. The spectral range was limited by an enhanced noise broadening of the Josephson linewidth at low frequencies and by increased dc Joule heating at high frequencies.