title: Observing atomic collapse resonances in artificial nuclei on graphene.
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.
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.forename: Dillon
authors.initials: D
authors.lastname: Wong
authors.forename: Andrey V
authors.initials: AV
authors.lastname: Shytov
authors.forename: Victor W
authors.initials: VW
authors.lastname: Brar
authors.forename: Sangkook
authors.initials: S
authors.lastname: Choi
authors.forename: Qiong
authors.initials: Q
authors.lastname: Wu
authors.forename: Hsin-Zon
authors.initials: HZ
authors.lastname: Tsai
authors.forename: William
authors.initials: W
authors.lastname: Regan
authors.forename: Alex
authors.initials: A
authors.lastname: Zettl
authors.forename: Roland K
authors.initials: RK
authors.lastname: Kawakami
authors.forename: Steven G
authors.initials: SG
authors.lastname: Louie
authors.forename: Leonid S
authors.initials: LS
authors.lastname: Levitov
authors.forename: Michael F
authors.initials: MF
authors.lastname: Crommie