Focused electron beam damaged YBCO Josephson junctions for THz device applications

We investigate the high-frequency properties of focused electron beam (FEB) damaged Josephson junctions for THz device applications. The FEB damaged YBCO junctions exhibit the resistively shunted junction (RSJ)-like current-voltage (I-V) curve and the microwave-induced Shapiro steps for all operation temperatures. At 4.2 K, the junctions exhibited the microwave-induced Shapiro steps up to 3 mV in dV/dI-V curves suggesting that the junctions can respond up to about 1.5 THz. To estimate the high frequency performance of the junctions, direct irradiation by a far infrared (FIR) laser at 0.76 THz is carried out and the clear first Shapiro step is observed for the junctions with I/sub C/R/sub N/ product of about 2 mV and at the operation temperature of 6 K.