Electronic Transport Behavior of Adatom- and Nanoparticle-Decorated Graphene

To induce a non-negligible spin-orbit coupling in monolayer graphene, for the purposes of realizing the Kane-Mele Hamiltonian, transition metal adatoms have been deposited in dilute amounts by thermal evaporation in situ while holding the device temperature near 4K. Electronic transport studies including measurements such as gate voltage dependent conductivity and mobility, weak localization, high field magnetoresistance (Shubnikov de Haas oscillations), quantum Hall, and nonlocal voltage were performed at low temperature before and after sequential evaporations. Studies of tungsten adatoms are consistent with literature regarding other metal adatoms on graphene but were unsuccessful in producing a spin-orbit signature, at least partially due to lithography residue inhibiting the adatoms’ ability to dope the graphene. Osmium adatoms on graphene behave differently from other adatoms in several ways. While all other measured adatoms donate electrons to graphene, osmium is observed to donate holes to graphene. In addition, tungsten and other adatoms directly affect the scattering potentials by causing a dominant Coulomb-like potential from isolated point charges. Osmium, on the other hand, does not obey this simple model. Separately, a claim was made in a recent study of Bi2Te3 nanoparticles on graphene showing tantalizing evidence of quantization in resistance coinciding with predictions for edge channel conduction. Our attempts to reproduce these observations have not been successful so far