Scanning tunneling spectroscopy and Dirac point resonances due to a single Co adatom on gated graphene

Abstract

Based on the standard tight-binding model of the graphene $\pi$-band electronic structure, the extended Hückel model for the adsorbate and graphene carbon atoms, and spin splittings estimated from density functional theory (DFT), the Dirac point resonances due to a single cobalt atom on graphene are studied. The relaxed geometry of the magnetic adsorbate and the graphene is calculated using DFT. The system shows strong spin polarization in the vicinity of the graphene Dirac point energy for all values of the gate voltage, due to the spin-splitting of Co 3d orbitals. We also model the differential conductance spectra for this system that have been measured in the scanning tunneling microscopy (STM) experiments of Brar {\em et al.} [Nat. Phys. {\bf 7}, 43 (2011)]. We interpret the experimentally observed behavior of the S-peak in the STM differential conductance spectrum as evidence of tunneling between the STM tip and a cobalt-induced Dirac point resonant state of the graphene, via a Co 3d orbital. The cobalt ionization state which is determined by the energy position of the resonance can be tuned by gate voltage, similar to that seen in the experiment.

12 pages, 4 figures

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• Induced exchange and spin-orbit effects by proximity in graphene on Ni and Co
• Voltage-controlled spin injection with an endohedral fullerene CoC${}_{60}$ dimer
• Spin-spin correlations of magnetic impurities in graphene
• Indirect exchange interaction between magnetic adatoms in graphene
• Coulomb bound states and resonances due to groups of Ca dimers adsorbed on suspended graphene
• Valley filters, accumulators, and switches induced in graphene quantum dots by lines of adsorbed hydrogen atoms
• The graphene sheet versus the 2DEG: a relativistic Fano spin-filter via STM and AFM tips