Zero photoemission from icosahedral superatoms

Résumé : Photoemission is expected to occur when the photon energy exceeds the binding energy of an electron, with the photoemission yield generally remaining non-zero above this threshold. Yet, it can be suppressed at specific photon energies, a phenomenon known as the Cooper minimum. Although complete suppression represents an extreme limit of this phenomenon, such zero photoemission has previously been reported only for atoms with an outermost s-type orbital and has never been observed in non-atomic systems. Here, we demonstrate the deliberate realization of zero photoemission from Ag12W-, an artificial icosahedral superatom, by observing a vanishing photoemission cross section 0.85 eV above the detachment threshold and reproducing this behavior in theoretical simulations. These simulations predict that zero photoemission can be common in nearly spherical nanoclusters, a prediction we experimentally confirm using Ag12Mo-, an isoelectronic counterpart of Ag12W-. Because superatoms offer systematic control over both size and elemental composition using the periodic table, our findings establish a route toward active control of photoemission in finite-size quantum systems and stimulate further investigations of underexplored physical phenomena such as nondipole effects.