  Electrons in graphene have fourfold spin and valley degeneracies owing to the
unique bipartite honeycomb lattice and an extremely weak spin-orbit coupling,
which can support a series of broken symmetry states. Atomic-scale defects in
graphene are expected to lift these degenerate degrees of freedom at the
nanoscale, and hence, lead to rich quantum states, highlighting promising
directions for spintronics and valleytronics. In this article, we mainly review
the recent scanning tunneling microscopy (STM) advances on the spin and/or
valley polarized states induced by an individual atomic-scale defect in
graphene, including a single-carbon vacancy, a nitrogen-atom dopant, and a
hydrogen-atom chemisorption. Lastly, we give a perspective in this field.
