  Topological superconductivity emerges in chains or arrays of magnetic atoms
coupled to a superconductor. However, the external controllability of such
systems with gate voltages is detrimental for their future implementation in a
topological quantum computer. Here we showcase the supramolecular assembly of
radical molecules on Pb(111), whose discharge is controlled by the tip of a
scanning tunneling microscope. Charged molecules carry a spin-1/2 state, as
confirmed by observing Yu-Shiba-Rusinov in-gap states by tunneling spectroscopy
at millikelvin temperature. Low energy modes are localized at island boundaries
with a long decay towards the interior, whose spectral signature is consistent
with Majorana zero modes protected by mirror symmetry. Our results open up a
vast playground for the synthesis of gate-tunable organic topological
superconductors.
