Precision measurement of hf/2e voltage at 63 K with superconducting weak-links under 100-120 GHz irradiation

A constriction of YBCO polycrystalline film, in which a network of grain boundary Josephson weak-links is naturally formed, behaves like a single Josephson element. Under 100-120 GHz irradiation, Shapiro-step like response is observed at voltage V_n=n(hf/2e) which is expected for a single Josephson weak-link. For verification of the Josephson-like effect, precision measurement of hf/2e voltage is made at 63 K by using the weak-link device of YBCO film. The measured values of inter-current-step voltage match the theoretical values with an error of 10 ppm. The result verifies that the frequency of oscillating pair current depends not on the partial potential difference but on the total potential difference between two bank electrodes, and that the HTS weak-links can be used as a precision voltage-reference source in millivolt and nanovolt regions