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Title: Are end states of magnetic atom chains on superconductors Majorana modes
Plain: Chains of iron atoms on superconducting lead show zero-energy states at their ends that were proposed as Majorana modes, but ordinary bound states can look similar, and the identification is unsettled.
Precise: STM on Fe atomic chains on Pb(110) (Nadj-Perge et al., Science 346, 602, 2014, doi:10.1126/science.1259327) and on later chains assembled atom by atom on superconductors shows zero-bias features at chain ends. Determine whether these are Majorana zero modes of a topological band of hybridized Yu-Shiba-Rusinov states (bound states induced by magnetic atoms in a superconductor). Required: a resolved bulk topological gap larger than the end-mode splitting, splitting that decays exponentially with chain length, and zero-bias conductance $2e^{2}/h$ in the strong-coupling tunnelling limit. An answer is yes or no for a specified chain system.
Settled by: Length-dependent spectroscopy on atom-by-atom assembled chains showing exponential decay of end-mode splitting with a resolved topological gap.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: Trivial interpretations of the end states are not excluded as of 2026, to this survey's knowledge.
Posed since: 2014