π-Loops With ds Josephson Junctions

• Published in: IEEE transactions on applied superconductivity 2019-08, Vol.29 (5), p.1-5
• Main Authors: Faley, M. I., Reith, P., Stolyarov, V. S., Golovchanskiy, I. A., Golubov, A. A., Hilgenkamp, H., Dunin-Borkowski, R. E.
• Format: Article
• Language: English
• Subjects: Coils; Critical current density; Current voltage characteristics; High-temperature superconductors; Josephson junctions; Magnetic field measurement; Magnetic fields; Magnetic flux; Magnetic resonance imaging; Mutual coupling; quantum computing; scanning probe microscopy; Substrates; Superconducting magnets; Superconducting quantum interference devices; superconducting quantum interference devices (SQUIDs); YBCO superconductors; Yttrium barium copper oxide
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2019.2892078

We fabricated Josephson junctions (JJs) between the d-wave superconductor (SC) YBa 2 Cu 3 O 7 -x (YBCO) and the swave SC Nb (ds-JJs) on graphoepitaxially buffered MgO substrates, studied ds-JJs at temperatures down to 30 mK and employed these JJs in π-loops. Current-voltage characteristics of dsJJs oriented along the [100] axis of YBCO exhibited up to a factor of 200 higher critical current densities than ds-JJs oriented along the [110] axis of YBCO. The critical current I and the IcRn product of [100]-oriented 3 μm wide ds-JJs are ~70 μA and ~200 μV, respectively, at 4.2 K. Rectangular arrays of up to 40 000 π-loops based on such ds-JJs were investigated using a low temperature scanning superconducting quantum interference device (SQUID) microscope. We observed ordering of spontaneously generated half integer magnetic flux quanta in the π-loops correlated with minute spurious background magnetic fields, as well as with configurations and mutual coupling of the π-loops. We manipulated the magnetic states of the π-loops by the local application of magnetic fields using nearby planar coils. This paper paves the way for the use of π-loops in computations that are based on annealing processes.