Speaker
Description
In multiterminal Josephson junctions (MTJJs), the Andreev bound state energies depend on multiple phase differences, enabling band structure engineering with external flux control. MTJJs are predicted to host non-trivial (non-Hermitian) topological phases and associated Weyl nodes in the synthetic Brillouin zone spanned by these superconducting phases [1,2]. In Ref. [3], spectroscopic measurements were performed on four-terminal Josephson junctions with phase control over all three superconducting phase differences, unveiling the presence of a tri-Andreev molecule, compatible with a topologically non-trivial model.
We predict that reflectionless scattering modes in MTJJs are a source of topological phase boundaries [4]. Our work provides an effective bulk-boundary correspondence by demonstrating a relationship between unity transmission modes and boundaries between topologically trivial and non-trivial regions, like in quantum Hall systems. Further insight into these systems can be provided by quantum geometry, where the so-called quantum weight [5] establishes bounds on the topological gap and existence of flat bands in MTJJs [6].
References
[1] R.-P. Riwar, et. al., Nature Commun. 7, 1 (2016)
[2] D. C. Ohnmacht, et. al., Phys. Rev. Lett. 134, 156601 (2025)
[3] T. Antonelli, et. al., Phys. Rev. X 15, 031066 (2025)
[4] D. C. Ohnmacht, et. al., arXiv:2503.10874 (2025)
[5] Y. Onishi and L. Fu, Phys. Rev. X 14, 011052 (2024)
[6] D. C. Ohnmacht, et. al. (in preparation)