Josephson Junctions and SQUIDs Created by Focused Helium-Ion-Beam Irradiation of YBa 2Cu3O7
Abstract
By scanning with a 30 -keV focused He ion beam (He -FIB) across YBa 2Cu3O7 (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 4.2 K , a transition from flux-flow to Josephson behavior occurs when jc decreases below approximately 2 MA /c m2 . 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 Vc≲1 mV . Devices on Mg O and LSAT substrates show nonhysteretic IVCs, while devices on SrTi O 3 show a small hysteresis. For all junctions, an approximate scaling Vc∝jc1 /2 is found. He -FIB irradiation with a high dose produces barriers with jc=0 and high resistances of 10 k Ω to 1 G Ω . 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 <500 n Φ0/H z1 /2 in the thermal white-noise limit for a device with 19 pH inductance.
- Publication:
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Physical Review Applied
- Pub Date:
- April 2019
- DOI:
- 10.1103/PhysRevApplied.11.044082
- arXiv:
- arXiv:1901.08039
- Bibcode:
- 2019PhRvP..11d4082M
- Keywords:
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- Condensed Matter - Superconductivity
- E-Print:
- Phys. Rev. Applied 11, 044082 (2019)