Two-dimensional topological superconductivity in Pb/Co/Si(111)

The examination of supposedly well-known condensed matter systems through the prism of topology has led to the discovery of new quantum phenomena that were previously overlooked. Just like insulators can present topological phases characterized by Dirac edge states, superconductors can exhibit topological phases characterized by Majorana edge states. In particular, one-dimensional topological superconductors are predicted to host zero energy Majorana fermions at their extremities. Zero bias anomalies localized at the edge of proximity induced superconducting wires were recently interpreted as fingerprints of the emergence of topological superconductivity [1,2].

By contrast, two-dimensional (2D) superconductors have a one-dimensional boundary which would naturally lead to propagating Majorana edge states characterized by a Dirac-like dispersion. We have recently observed some hint of dispersive Majorana edge states in a single atomic layer Pb superconductor. This material has strong triplet correlations but is not topological by itself [3]. We will show that by applying a Zeeman field with the help of a buried Co-Si nano-magnet one can provoke a transition to a topological state [4].

In addition to their dispersive edge states, 2D topological superconductors are also supposed to support localized Majorana bound states in their vortex cores. We will show that some recent measurements seem to support this theoretical prediction [5].

References
[1] V. Mourik et al., Science 336, 1003 (2012)
[2] S. Nadj-Perge, et al., Science 346, 602 (2014)
[3] C. Brun et al., Nature Phys. 444, 10 (2014)
[4] G. C. Ménard, et al., Nature Comm, 8, 2040 (2017)
[5] G. C. Ménard, et al., arXiv:1810.09541