Observing Atomic Collapse in Graphene

Relativistic quantum mechanics predicts that super-heavy atoms possess unique properties not shared by ordinary atoms. In particular, a very strong electric field around the nucleus should result in ``atomic collapse,'' with an electron component falling onto the nucleus and a positron component escaping to infinity. Predicted by Dirac 80 years ago, atomic collapse has thus far remained experimentally out of reach using accelerator-based techniques. Here we report the observation of atomic collapse on gated graphene devices. The energy and spatial dependence of the atomic collapse state was measured using scanning tunneling microscopy (STM).