Atom-by-Atom Fabricated Magnet-Superconductor Hybrid Systems as Ideal Platforms for Realizing Topological Superconductivity and Associated Majorana Zero Modes

One of the major challenges for the future of quantum computation is the drastic reduction of the error rate associated with quantum decoherence phenomena. Robust topological qubits, as realized by Majorana states, may ultimately provide a solution and constitute a new direction of topological quantum computation. However, an unambiguous identification of Majorana states requires well defined model-type platforms.

We make use of STM-based single atom manipulation techniques in order to fabricate well-defined defect-free 1D atomic chains of magnetic adatoms (Mn, Fe, Co) on s-wave superconductors (Re, Ta, Nb) with high spin-orbit coupling [1-10]. The spin structure of these low-dimensional adatom arrays is characterized by spin-polarized STM [4,11], while scanning tunneling spectroscopy reveals the evolution of the spatially and energetically resolved local density of states as well as the emergence of zero-energy bound states at both chain ends above a critical chain length [1,7]. In order to confirm the interpretation of the zero-energy states as Majorana quasiparticles, we use Bogoliubov quasiparticle interference (QPI) mapping of the 1D magnet-superconductor hybrid systems for directly probing the non-trivial band structure of the topological phases as well as the bulk-boundary correspondence [5]. Such experiments constitute the ultimate test and rigorous proof for the existence of topologically non-trivial zero-energy modes [6,7]. We will focus on recent experiments which aim at optimizing the magnitude of the topological gap and therefore the robustness of Majorana modes by heterostructure engineering involving superconducting substrates with high T_c and interfacial thin films exhibiting large spin-orbit coupling.      

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