In 2017, experimental evidence for one-dimensional chiral Majorana fermions was shown in a topological insulator device, but has been difficult to replicate. Now, Morteza Kayyalha and co-workers have completed a comprehensive study to ascertain why.
It turns out that the interface between the topological insulator and the superconducting layer is crucial. The authors measured devices where the transport signatures and interface characteristics could be extracted at the same time. The transport signatures previously associated with the chiral Majorana states existed whenever there was a transparent interface between the topological insulator and the superconductor. This strong coupling at the interface allows the superconductor to act as a short, modifying the transport properties from the theoretical predictions.
This doesn’t rule out the possibility that the old experiments observed chiral Majorana modes, but it certainly shows that more evidence is needed.
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Abergel, D. Majorana transparency. Nat. Phys. 16, 123 (2020). https://doi.org/10.1038/s41567-020-0801-4