Josephson junctions and SQUIDs created by focused helium-ion-beam irradiation of YBa2Cu3O7

Josephson junctions and SQUIDs created by focused helium-ion-beam irradiation of YBa2Cu3O7
Müller B, Karrer M, Limberger F, Becker M, Schröppel B, Burkhardt CJ, Kleiner R, Goldobin E, Koelle D
Phys. Rev. Applied accepted

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 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 non-hysteretic IVCs, while devices on SrTiO3 show a small hysteresis. For all junctions an approximate scaling Vcj1/2c is found. He-FIB irradiation with high dose produces barriers with jc=0 and high resistances of 10kΩ1GΩ. 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 definition of the SQUID hole and the junctions. The SQUIDs show high performance, with flux noise $