Fabrication of Josephson junctions with nano-injectors and investigation of fractional flux quanta.
Final Report Abstract
Creating controllable and tunable phase discontinuities in Josephson junctions using nano-injectors is a powerful and flexible tool for designing new types of Josephson junctions and systems with desired and functional properties. Technologically, the fabrication of such nano-injectors was successful down to sizes 500 nm and the junction width 800 nm. Simultaneously, some limiting factors such as (a) trapping of parasitic Abrikosov vortices in the JJ between injectors, (b) small critical current of injector nano-wires and (c) sensitivity to small defects in the region between injectors, where the current density has maximum, appeared. Therefore, further decrease of the injector sizes makes not much sense presently. On experimental side, we showed that nano-injector pairs indeed create well localized phase discontinuities and demonstrated ϕ Josephson junctions based on this idea. Such junction can also be used in quantum circuits as it has very low damping in comparison with the original generation of ϕ junctions based in junction with specially tailored ferromagnetic interlayer. As an example, we have demonstrated experimentally the macroscopic quantum tunneling of the phase from both wells (ground states) states of ϕ Josephson junction. On the other hand, the creation and investigation of multi-fractional-vortex systems (in longer junctions) turns to be rather difficult and less reproducible. Even the ϕ JJ of moderate length has rather small margins. In this sense, the alternative systems like 0-π SQUIDs or 3 junction 0-0-π SQUIDs are more promising for applications in terms of margins as our first theoretical estimations show. They will also benefit from the possibility to phase-shift them using tiny current injectors.
Publications
- “Fractional vortex in asymmetric 0-π long Josephson junctions”, Phys. Rev. B 87, 224501 (2013)
E. Goldobin, R. Kleiner, D. Koelle
(See online at https://doi.org/10.1103/PhysRevB.87.224501) - “Josephson junctions with tunable current-phase relation”, Phys. Rev. B 90, 184502 (2014)
A. Lipman, R.G. Mints, R. Kleiner, D. Koelle, E. Goldobin
(See online at https://doi.org/10.1103/PhysRevB.90.184502) - “Tunable ±ϕ , ϕ0 and ϕ0 ± ϕ Josephson junction”, Phys. Rev. B 91, 214511 (2015)
E. Goldobin, D. Koelle, R. Kleiner
(See online at https://doi.org/10.1103/PhysRevB.91.214511) - “Effective model for a short Josephson junction with a phase discontinuity”, Phys. Rev. B 93, 134514 (2016)
E. Goldobin, S. Mironov, A. Buzdin, R. G. Mints, D. Koelle, and R. Kleiner
(See online at https://doi.org/10.1103/PhysRevB.93.134514) - “Model I -V curves and figures of merit of underdamped deterministic Josephson ratchets”, Phys. Rev. E 94, 032203 (2016)
E. Goldobin, R. Menditto, D. Koelle and R. Kleiner
(See online at https://doi.org/10.1103/PhysRevE.94.032203) - “Phase retrapping in a ϕ Josephson junction: Onset of the butterfly effect”, Phys. Rev. B 93, 174506 (2016)
R. Menditto, H. Sickinger, M. Weides, H. Kohlstedt, M. Žonda, T. Novotný, D. Koelle, R. Kleiner, and E. Goldobin
(See online at https://doi.org/10.1103/PhysRevB.93.174506) - “Tunable ϕ Josephson junction ratchet”, Phys. Rev. E 94, 042202 (2016)
R. Menditto, H. Sickinger, M. Weides, H. Kohlstedt, D. Koelle, R. Kleiner and E. Goldobin
(See online at https://doi.org/10.1103/PhysRevE.94.042202) - “Anomalous Josephson effect controlled by an Abrikosov vortex”, Phys. Rev. B 96, 214515 (2017)
S. Mironov, E. Goldobin, D. Koelle, R. Kleiner, Ph. Tamarat, B. Lounis, and A. Buzdin
(See online at https://doi.org/10.1103/PhysRevB.96.214515) - “Evidence of macroscopic quantum tunneling from both wells in a ϕ Josephson junction”, Phys. Rev. B 98, 024509 (2018)
R. Menditto, M. Merker, M. Siegel, D. Koelle, R. Kleiner, and E. Goldobin
(See online at https://doi.org/10.1103/PhysRevB.98.024509)
