New strategies for the mutual synchronization of very large Josephson junction networks
Final Report Abstract
The aim of the original project was to investigate new strategies for the mutual synchronization of very large Josephson junction networks, with the objective to significantly advance submm wavelength radiation sources based on phase-synchronized Josephson junctions (JJs). The sources should consist of large 1D or 2D JJ arrays, with high output power and tunability. The arrays were based on either SNS JJs ("S" = superconductor, "N" = normal metal), SN bilayers consisting of MoN (S layer) and Cu (N layer), or YBa2Cu3O7 (YBCO) JJs created by focused helium ion beam patterning (HIM) or focused neon ion beam patterning (NIM). We started with large Nb/NbSi/ Nb junction-based arrays containing up to about 1600 JJs. Low-temperature scanning laser microscopy showed that standing electromagnetic waves built up along these arrays. A detailed data analysis revealed that the standing waves are formed by surface plasmon–type electromagnetic waves propagating at the electrode-substrate interface, demonstrating that surface waves provide an effective mechanism for longrange coupling and phase-locking of large junction arrays. With respect to SN bilayers, lithographically pre-structured MoN/Cu microbridges were further nano-structured by HIM and electrically characterized. The bilayers were expected to show excellent electric JJ characteristics, once patterned on the nanoscale. We indeed found promising electrical properties. The preliminary results also showed that the HIM patterning into JJs has critical issues, like a swelling of the substrate introduced by the ion beam. The issue was solved by replacing HIM by NIM. These common activities stopped in 2022. The study of YBCO based junctions created by HIM was centered in Tübingen throughout the project. After some optimization we were able to produce JJs with junction characteristics (IcR products) that are good enough to facilitate a high frequency emitter up to THz frequencies. In parallel we made first attempts to create large arrays of YBCO based JJs. These attempts were not successful. We thus went back to investigate the mutual synchronization of two HIM-patterned JJs. We found that the introduction a HIM-written resistive and inductive element in parallel to the junctions induces an almost textbook-like synchronization up to THz frequencies. The scheme can be generalized to larger arrays.
Publications
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Direct Visualization of Phase-Locking of Large Josephson Junction Arrays by Surface Electromagnetic Waves. Physical Review Applied, 14(2).
Galin, M.A.; Rudau, F.; Borodianskyi, E.A.; Kurin, V.V.; Koelle, D.; Kleiner, R.; Krasnov, V.M. & Klushin, A.M.
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Terahertz emission from mutually synchronized standalone Bi2Sr2CaCu2O8+x intrinsic-Josephson-junction stacks. Physical Review Applied, 22(4).
Wieland, Raphael; Kizilaslan, Olcay; Kinev, Nickolay; Dorsch, Eric; Guénon, Stefan; Song, Ziyu; Wei, Zihan; Wang, Huabing; Wu, Peiheng; Koelle, Dieter; Koshelets, Valery P. & Kleiner, Reinhold
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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.
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YBa2Cu3O7 Josephson diode operating as a high-efficiency ratchet.
C. Schmid, A. Jozani, R. Kleiner, D. Koelle & E. Goldobin
