Würzburg ToCoTronics Colloquium

Magnetic chains on s-wave superconductors evoke so-called Shiba bands inside the gap of the substrate. If these bands experience sufficiently strong spin-orbit coupling and overlap with the Fermi energy, a topologically nontrivial minigap can open up which may protect zero energy Majorana bound states localized at the chains two ends. We study artificial spin chains, built atom-by-atom [1], with respect to such phenomena. By variation of substrate and adatom species and interatomic distances in the chain [2-5], we adjust the energies of the multi-orbital Yu-Shiba-Rusinov states induced by the adatoms [2,3], their hybridizations [4], as well as the
chains’ spin structures [5]. This enables us to tailor the multi-orbital Shiba bands formed by hybridizing Yu-Shiba-Rusinov states such that topologically nontrivial minigaps open [6] and precursors of Majorana bound states appear [7]. Due to a narrow energetical width of the topological minigaps in the systems that have been studied to date, the two components of the Majorana precursors from the two chain ends strongly hybridize, such that a desired protection by the topological minigap is not realized. In this talk, I will review our work, present our most recent strategies in order to increase the width of the topological minigap [8-10], and show experimental methods we developed to decide on the topologically trivial or non-trivial nature of close-to-zero-energy end states. I acknowledge funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) via the Cluster of Excellence ’Advanced Imaging of Matter’ (EXC 2056-project ID 390715994) and via the SFB-925-project 170620586.

References
1. D.-J. Choi, N. Lorente, J. Wiebe, K. von Bergmann, A. F. Otte, and A. J. Heinrich,
Rev. Mod. Phys. 91, 041001 (2019).
2. L. Schneider, M. Steinbrecher L. Rózsa, J. Bouaziz, K. Palotás, M. dos Santos Dias, S. Lounis,
J. Wiebe, and R. Wiesendanger, npj Quantum Materials 4, 42 (2019).
3. L. Schneider, S. Brinker, M. Steinbrecher, J. Hermenau, Th. Posske, M. dos Santos Dias,
S. Lounis, R. Wiesendanger, and J. Wiebe, Nature Commun. 11, 4707 (2020).
4. P. Beck, L. Schneider, L. Rózsa, K. Palotás, A. Lászlóffy, L. Szunyogh, J. Wiebe,
and R. Wiesendanger, Nature Commun. 12, 2040 (2021).
5. L. Schneider, P. Beck, J. Wiebe, and R. Wiesendanger,
Science Advances 7, eabd7302 (2021).
6. L. Schneider, P. Beck, T. Posske, D. Crawford, E. Mascot, S. Rachel, R. Wiesendanger,
and J. Wiebe, Nature Physics 17, 943 (2021).
7. L. Schneider, P. Beck, J. Neuhaus-Steinmetz, T. Posske, J. Wiebe, and R. Wiesendanger,
Nature Nanotechnology 17, 384 (2022).
8. P. Beck, L. Schneider, L. Bachmann, J. Wiebe, and R. Wiesendanger,
Phys. Rev. Materials 6, 024801 (2022).
9. P. Beck, L. Schneider, R. Wiesendanger, and J. Wiebe,
arXiv:2205.10062 [cond-mat.supr-con] (2022).
10. P. Beck, L. Schneider, R. Wiesendanger, and J. Wiebe,
arXiv:2205.10073 [cond-mat.supr-con] (2022).

This talk is also broadcasted via zoom. To enter the meeting, follow the link:
https://uni-wuerzburg.zoom.us/j/63035236463?pwd=U1FXWDJpS3JNajk4cFhoNjRDMSsvUT09