Spectral range of the ac Josephson effect in [001]-tilt YBa2Cu3O7-x bicrystal junctions

We have studied the ac Josephson effect in YBa₂Cu₃O_7-x bicrystal junction by monitoring the voltage dependence of the dc current response ΔI(V) induced by low-power monochromatic radiation with the frequencies f_i. The intensity of odd-symmetric resonances in the function ΔI(V) near the voltages V_i=hf_i/2e is proportional to the amplitude of Josephson oscillations at the frequency f_i. The resonance intensities have been mapped as a function of the Josephson frequency f_i in the range from 5 GHz to 5 THz, the junction resistance R_n in the range from 0.4 to 80 Ohm and junction characteristic voltages I_cR_n in the range from 5 μV to 1.8 mV. The central frequency of the range was scaled with the I_cR_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.