Science http://doi.org/wdr (2014)

The Majorana fermion — the hypothetical particle that is its own antiparticle — remains as controversial and elusive as its namesake. The search for Majorana fermions in the form of quasiparticle bound states in condensed-matter systems, fuelled by their possible use as topological qubits, has been underway for some time now. In 2012, the first sightings were reported in a semiconductor nanowire in contact with a superconducting electrode. But the initial excitement was tempered by the possibility that the signal was actually due to the Kondo effect or disorder.

Stevan Nadj-Perge and colleagues took the hunt for Majorana fermions to new territory: a chain of iron atoms on a superconducting lead surface. The ferromagnetic interaction between the atoms, and the strong spin–orbit coupling of the superconductor, provide the necessary ingredients for topological superconductivity. The enhanced resolution of scanning tunnelling microscopy measurements allowed the team to extract strong evidence for the existence of Majorana fermions. But whether the search is now finally over remains to be seen.