  Massless Dirac fermions have been observed in various materials such as
graphene and topological insulators in recent years, thus offering a
solid-state platform to study relativistic quantum phenomena. Single quantum
dots (QDs) and coupled QDs formed with massless Dirac fermions can be viewed as
artificial relativistic atoms and molecules, respectively. Such structures
offer a unique platform to study atomic and molecular physics in the
ultra-relativistic regime. Here, we use a scanning tunneling microscope to
create and probe single and coupled electrostatically defined graphene QDs to
unravel the unique magnetic field responses of artificial relativistic
nanostructures. Giant orbital Zeeman splitting and orbital magnetic moment are
observed in single graphene QDs. While for coupled graphene QDs, Aharonov Bohm
oscillations and strong Van Vleck paramagnetic shift are observed. Such
properties of artificial relativistic atoms and molecules can be leveraged for
novel magnetic field sensing modalities.
