  Impurities exist inevitably in two-dimensional materials as they
spontaneously adsorb onto the surface during fabrication, usually exerting
detrimental effects on electronic transport. Here, we focus on a special type
of impurities that preferentially adsorb onto the hollow regions of graphene
nanoribbons (GNRs), and study how they affect the quantum transport in GNRs.
Contrary to previous knowledge that random adatoms should localize electrons,
the so-called Anderson localization, noteworthy quantized conductance peaks
(QCPs) are observed at specific electron energies. These QCPs are remarkably
robust against variations in system size, GNR edge, and adatom properties, and
they can reappear at identical energies following an arithmetic sequence of
device width. Further investigation of wavefunction reveals a unique transport
mode at each QCP energy which transmits through disordered GNRs
reflectionlessly, while all the others become fully Anderson localized,
indicating the survival of quantum ballistic transport in the localized regime.
Our findings highlight the potential utility of hollow adatoms as a powerful
tool to manipulate the conductivity of GNRs, and deepen the understanding of
the interplay between impurities and graphene.
