AC Response Across the Metal Insulator Transition of YBCO Josephson Junctions Fabricated with a Helium Ion Beam
Using focused helium ion beam (FHIB) irradiation, we fabricated in-plane, high-Tc YBCO Josephson junctions. By varying the dose of the irradiation, we tune the junction barriers from metallic (SNS) to insulating (SIS) 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.