Experimental evidence for the autonomous Bloch oscillations in single Josephson junctions

The charging effects in single ultrasmall Josephson junctions with area S approximately=0.01 mu m/sup 2/ have been studied at low temperatures, T approximately=50 mK. The junctions were isolated from the electromagnetic environment by high-ohmic metallic resistors with R approximately=500 k Omega inserted into the current and voltage leads. For improvement of the isolation by a factor of two, additional tunnel junctions of the same area were inserted into the current leads. Existence of Bloch oscillations was demonstrated by observation of the self-selective videoresponse of the junction under irradiation by a small amplitude-modulated RF signal. The amplitude of the signal was 2-3 orders smaller than in previous experiments. The amplitude of the response had a linear dependence on the power of the signal, and the DC current position of its peak was proportional to the frequency of the signal with the relation I=+or-2 ef. All these observations can be explained as an interaction of the small external signal with the narrowband Bloch oscillations generated by the junction.<>