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 protects 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 YuShiba 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 these topological minigaps, the two components of the Majorana precursors from the two chain ends strongly hybridize, such that the desired protection by the topological minigap is not realized. In this talk, I will present our most recent experimental strategies in order to increase the width of the topological minigap [8-10] which will eventually lead to isolated and topologically protected Majorana bound 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.

[1] D.-J. Choi, N. Lorente, J. Wiebe, K. von Bergmann, A. F. Otte, 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, 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, J. Wiebe, Nature
Commun. 11, 4707 (2020).
[4] P. Beck, L. Schneider, L. Rózsa, K. Palotás, A. Lászlóffy, L. Szunyogh, J. Wiebe, R. Wiesendanger, Nature Commun. 12, 2040 (2021).
[5] L. Schneider, P. Beck, J. Wiebe, R. Wiesendanger, Science Advances 7, eabd7302 (2021).
[6] L. Schneider, P. Beck, T. Posske, D. Crawford, E. Mascot, S. Rachel, R. Wiesendanger, J. Wiebe, Nat. Phys. 17, 943 (2021).
[7] L. Schneider, P. Beck, J. Neuhaus-Steinmetz, T. Posske, J. Wiebe, R. Wiesendanger, Nature Nanotechnology 17, 384 (2022).
[8] P. Beck, L. Schneider, L. Bachmann, J. Wiebe, R. Wiesendanger, Phys. Rev. Materials 6, 024801 (2022).
[9] P. Beck, L. Schneider, R. Wiesendanger, J. Wiebe, arXiv:2205.10062 [cond-mat.supr-con] (2022).
[10] P. Beck, L. Schneider, R. Wiesendanger, J. Wiebe, arXiv:2205.10073 [cond-mat.supr-con] (2022.)