The large integrated luminosity collected by the ATLAS detector during
Run 2 of the LHC provides a huge sample of top quark physics events in
which to study rare Standard Model (SM) processes and probe for the
presence of new physics. New couplings beyond the SM (BSM) could
enhance the rate of very rare top quark processes providing
sensitivity for flavour-changing neutral current (FCNC) or lepton
flavour-violating (LFV) interactions of the top quark. In the SM, both
FCNC and LFV interactions involving the top quark are so small that
any significant measurable cross-section for such a process is an
indication of new physics. The ATLAS experiment has recently reported
the observation of the rare SM 4-top production process which is
sensitive to new physics. Additionally, dedicated searches have been
performed for FCNC couplings of the top quark with a photon, gluon, Z
boson or Higgs boson, as well as LFV couplings to another up-type
quark, a muon and a tau lepton. In this seminar the most recent
results will be presented and the experimental challenges and
systematic uncertainties will be discussed.