Josephson nano-junctions fabricated with a focused He-ion beam

• Applicant: Dr. Edward Goldobin
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 424544156

• Final Report Year: 2024

Final Report Abstract

He-ion microscope (HIM) turned out to be a unique tool for modifying the properties of cuprate superconductors, such as YBCO, on the nanoscale using focused He-ion beam (He-FIB). Using HIM we were able to fabricate a number of circuit elements such as barrier Josephson junctions (bJJs) , constriction Josephson junctions (cJJs), resistors, define the boundaries, walls and holes — all only using He-FIB in one technological step. More advanced circuits such as nano-SQUIDs or Josephson diodes with record parameters were demonstrated. The resolution (minimum feature size) achievable using this technique is defined by the He-FIB spot size (diameter), which is typically 6 . . . 10 nm depending on HIM settings. However, writing boundaries, walls and holes with high irradiation dose causes amorphization in the YBCO, which results in mechanical stress and spoils the resolution up to ∼ 100 nm. Apart from studying physical processes that take place within irradiated regions (TEM, local XRD, time evolution and healing) we demonstrated two advanced devices. First, we demonstrated the Josephson diode with record parameters (asymmetry, size, operation temperature, thermodynamic efficiency) fully written by He-FIB. Second, we demonstrated the miniaturization limits by fabricating cJJs and two-cJJ-nano-SQUIDs with the nominal constriction size ∼ 10 nm exhibiting excellent figures of merit.

Publications

• Fractional positional jumps in stochastic systems with tilted periodic double-well potentials. Physical Review B, 110(5).
  Žonda, Martin; Belzig, Wolfgang; Goldobin, Edward & Novotný, Tomáš
  
• Temporal evolution of electric transport properties of YBa2 Cu3 O7−δ Josephson junctions pro duced by focused-helium-ion-beam irradiation. Physical Review Applied, 21(1).
  Karrer, M.; Wurster, K.; Linek, J.; Meichsner, M.; Kleiner, R.; Goldobin, E. & Koelle, D.
  
• THz Properties of He-FIB YBa2Cu3O7-x Josephson Junctions. IEEE Transactions on Applied Superconductivity, 34(3), 1-5.
  Pröpper, M.; Hanisch, D.; Schmid, C.; Ritter, P. J.; Neumann, M.; Goldobin, E.; Koelle, D.; Kleiner, R.; Schilling, M. & Hampel, B.
  
• YBa2 Cu3 O7 Josephson diode operating as a high-efficiency ratchet
  Christoph Schmid, Alireza Jozani, Reinhold Kleiner, Dieter Koelle & Edward Goldobin