Transport signatures of Kondo physics and quantum criticality in graphene with magnetic impurities
Localized magnetic moments have been predicted to develop in graphene samples with vacancies or adsorbates. The interplay between such magnetic impurities and graphene's Dirac quasiparticles leads to remarkable many-body phenomena, which have so far proved elusive to experimental efforts. In this article, we study the thermodynamic, spectral and transport signatures of quantum criticality and Kondo physics of a dilute ensemble of atomic impurities in graphene. We consider vacancies and adatoms that either break or preserve graphene's $C_{3v}$ and inversion symmetries. In a neutral graphene sample, all cases display symmetry-dependent quantum criticality, leading to enhanced impurity scattering for asymmetric impurities, in a manner analogous to bound-state formation by nonmagnetic resonant scatterers. Kondo correlations emerge only in the presence of a back gate, with estimated Kondo temperatures well within the experimentally accessible domain for all impurity types. For symmetry-breaking impurities at charge neutrality, quantum criticality is signaled by $T^{-2}$ resistivity scaling, leading to full insulating behavior at low temperatures, while low-temperature resistivity plateaus appear both in the non-critical and Kondo regimes. By contrast, the resitivity contribution from symmetric vacancies and hollow-site adsorbates vanishes at charge neutrality and for arbitrary back gate voltages, respectively. This implies that local probing methods are required for the detection of both Kondo and quantum critical signatures in these symmetry-preserving cases.