Nature Nanotech. http://doi.org/5dp (2015)

There are three types of fermions in condensed-matter systems: Dirac, Weyl and Majorana. Whereas Dirac fermions are now commonplace thanks to graphene, and experimental evidence for Weyl fermions is growing stronger, Majorana fermions currently remain as elusive as Ettore Majorana himself. Topological superconductors are predicted to host these quasiparticles, but experimentally realizing topological superconductivity is not trivial. Vlad Pribiag and colleagues may have provided a suitable two-dimensional system for this exotic state.

Using superconducting quantum interference, the authors provide evidence for superconductivity in the edge modes of a semiconductor quantum-well heterostructure. The authors were able to electrically tune from bulk to edge-mode superconductivity, but as the edge-mode regime is only observable when the bulk is highly resistive, they associate this with a two-dimensional topological phase.

Topological superconductivity in such edge states would not only give access to Majorana fermions, but also provide a platform for realizing localized Majorana modes. And as these modes would obey non-Abelian statistics and have topological characteristics, they are the highly sought-after building blocks for a fault-tolerant quantum computer.