AC response across the metal–insulator transition of YBCO Josephson junctions fabricated with a helium-ion beam

Using focused helium-ion beam irradiation, we fabricated in-plane, high-Tc YBa2Cu3O7−δ Josephson junctions. By varying the dose of the irradiation, we tune the junction barriers from metallic to insulating and investigate how this transition affects microwave-driven dynamics. As the barrier transitions from metallic to insulating, the oscillatory response of the Shapiro steps to the RF power changes dramatically. On either side of the metal–insulator transition, the devices exhibit clean integer Shapiro steps without half-integer features, demonstrating that the current–phase relation is dominated by the first harmonic and that the excess current is minimal. The current–voltage response is well described by the resistively, capacitively shunted junction model assuming a single-harmonic current–phase relation. This behavior indicates well-controlled junction properties suitable for a wide range of superconducting electronics, including detectors, mixers, and high-density integrated circuits.