Observing Atomic Collapse Resonances in Artificial Nuclei on Graphene

TL;DR

This study reports the experimental observation of atomic collapse resonances in artificial nuclei created on graphene, confirming theoretical predictions about relativistic quantum effects in a condensed matter system.

Contribution

First direct observation of atomic collapse resonances in artificial nuclei on graphene, demonstrating relativistic quantum phenomena in a controllable solid-state platform.

Findings

Resonances observed around charged calcium dimer clusters on graphene.

Energy and spatial profiles of the collapse states measured with STM.

Unexpected behavior when the states are occupied by electrons.

Abstract

Relativistic quantum mechanics predicts that when the charge of a superheavy atomic nucleus surpasses a certain threshold, the resulting strong Coulomb field causes an unusual atomic collapse state; this state exhibits an electron wave function component that falls toward the nucleus, as well as a positron component that escapes to infinity. In graphene, where charge carriers behave as massless relativistic particles, it has been predicted that highly charged impurities should exhibit resonances corresponding to these atomic collapse states. We have observed the formation of such resonances around artificial nuclei (clusters of charged calcium dimers) fabricated on gated graphene devices via atomic manipulation with a scanning tunneling microscope. The energy and spatial dependence of the atomic collapse state measured with scanning tunneling microscopy revealed unexpected behavior when occupied by electrons.