Quantum Engineering of Majorana Fermions*

The experimental observation of Majorana states in topological superconductors represents a major breakthrough in realizing their applications in topological quantum computing. This has stimulated the search for new possibilities to engineer Majorana states at the nanoscale, in particular using magnetic-superconducting hybrid (MSH) structures in which islands of magnetic adatoms are placed on the surface of s-wave superconductors.

In this talk, I provide several examples for the quantum engineering of Majorana fermions in MSH systems [1,2]. First, I will report the results of a theory-experiment collaboration demonstrating the ability to tune between a topological phase exhibiting chiral Majorana edge modes and a trivial phase in Fe-Re MSH structures using interface engineering [1]. Second, I will show that one can create a topological switch in MSH systems by imprinting magnetic skyrmions, allowing one to write and delete topological phases. Similarly, it is possible to engineer chiral Majorana states of arbitrary shape through the creation of magnetic domain walls. Third, I show that it is possible to continuously tune MSH systems between 2D and 1D topological phases using atomic manipulation, and thus to change the character of the associated Majorana modes. Finally, I will demonstrate that Josephson scanning tunneling spectroscopy is a crucial tool in identifying topological phases [3].

[1] Atomic-Scale Interface Engineering of Majorana Edge Modes in a 2D Magnet-Superconductor Hybrid System, A. Palacio-Morales, E. Mascot, S. Cocklin, H. Kim, S. Rachel, D. K. Morr and R. Wiesendanger, arXiv:1809.04503
[2] Quantized charge transport in chiral Majorana edge modes, S. Rachel, E. Mascot, S. Cocklin, M. Vojta, and D.K. Morr, Phys. Rev. B 96, 195162 (2017).
[3] M. Graham and D.K. Morr, Phys. Rev. B 96, 184501 (2017)