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Novel Josephson junctions

Novel high-Tc step-edge Josephson junctions for biomagnetometers

Ar+ ion beam etching and negative photoresist nLOF2020 were used for the preparation of 45o steps on (001) MgO substrates. The step was covered by a double buffer layer: a bottom 10-nm-thick non-superconducting YBa2Cu3O7-x (YBCO) film as a “seed” layer that was covered by a 30-nm-thick SrTiO3 film as a “blocking” layer. High-resolution transmission electron microscopy images show two 45o [100]-tilted grain boundaries in the top YBCO layer: one at the top corner of the step and other at the lower corner of the step. The top YBCO layer has a thickness of 200 nm, a superconducting transition temperature Tc of 93 K and a critical current density of 5 MA/cm2 at 77 K. The 2-µm-wide Josephson junctions have normal state resistance Rn=20 ohm and IcRn product 800 µV at 77 K. Magnetic field resolution of high-Tc SQUID biomagnetometers 2 fT/rt(Hz) at 77 K was achieved.

Copyright: M. FaleyHigh-Tc step-edge Josephson junction on MgO substrate.

  1. M. I. Faley, Patent US 9666783 B2 granted 30.05.2017.
  2. M. I. Faley et al., Superconductor Science and Technology 30, 083001 (2017).
  3. M. I. Faley et al., IEEE Transactions on Applied Superconductivity 28 (4) 1600505 (2018).

Josephson junctions between d-wave and s-wave superconductors

Josephson junctions between d-wave superconductor YBa2Cu3O7-x (YBCO) and s-wave superconductor Nb were realized. The normal conducting Au barrier between Nb and YBCO served also as a diffusion barrier for oxygen ions. In π-loops based on such junctions the positive [100] and negative [010] lobes of thin film of YBCO are connected by Nb film. Exactly half quantum of magnetic flux is appeared due to the spontaneously induced persistent currents in such pi-loop. Such π-loops are intended for implementation in self-biased superconducting flux qubits that have potentially longer coherence time because they are naturally decoupled from perturbations produced by the environment: their double-well energy potential is symmetrized by integration in the qubit a pi-junction instead of using a conventional inductance with an external current sources.

Copyright: M. FaleySEM image of YBCO-Au-Nb Josephson edge junction produced at PGI-5 FZJ.

  1. Novel JosephsonH. Hilgenkamp et al., Nature 422, 50, (2003).
  2. M. I. Faley et al., ASC'2018 (2018).