ac Josephson effect in superconducting all‐Nb thin‐film nanobridges up to 693 GHz

All‐niobium thin‐film nanobridges were fabricated with bridge sizes of 40‐nm length, 50‐nm width, and 100‐nm thickness. We investigated the performance of the nanobridges by monitoring Shapiro steps induced on the current‐voltage curves by an optically pumped far‐infrared laser. These steps have been observed up to 693 GHz (433 μm). This is a twofold increase over that previously reported on thin‐film nanobridges.