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Josephson Junctions and SQUIDs Created by Focused Helium-Ion-Beam Irradiation of Y Ba 2 Cu 3 O 7

Authors: B. Müller, M. Karrer, F. Limberger, M. Becker, B. Schröppel, C.J. Burkhardt, R. Kleiner, E. Goldobin, and D. Koelle

Physical Review Applied volume 11, 044082 (2019)

Abstract: By scanning with a 30keV focused He ion beam (He-FIB) across YBa2Cu3O7 (YBCO) thin-film microbridges, we create Josephson barriers with critical current density jc adjustable by irradiation dose D. The dependence jc(D) yields an exponential decay. At 4.2K, a transition from flux-flow to Josephson behavior occurs when jc decreases below approximately 2MA/cm2. The Josephson junctions exhibit current-voltage characteristics (IVCs) that are well described by the resistively and capacitively shunted junction model, without excess current for characteristic voltages Vc1mV. Devices on MgO and LSAT substrates show nonhysteretic IVCs, while devices on SrTiO3 show a small hysteresis. For all junctions, an approximate scaling Vcj1/2c is found. He-FIB irradiation with a high dose produces barriers with jc=0 and high resistances of 10kΩ to 1GΩ. This provides the possibility to write highly resistive walls or areas into YBCO using a He-FIB. Transmission electron microscopy reveals an amorphous phase within the walls, whereas for lower doses the YBCO stays crystalline. We have also “drawn” superconducting quantum-interference devices (SQUIDs) by using a He-FIB for the definition of the SQUID hole and the junctions. The SQUIDs show high performance, with flux noise <500nΦ0/Hz1/2 in the thermal white-noise limit for a device with 19pH inductance.

DOI: 10.1103/PhysRevApplied.11.044082

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