Defect-mediated spin relaxation and dephasing in graphene.

A principal motivation to develop graphene for future devices has been its promise for quantum spintronics. Hyperfine and spin-orbit interactions are expected to be negligible in single-layer graphene. Spin transport experiments, on the other hand, show that graphene's spin relaxation is orders of magnitude faster than predicted. We present a quantum interference measurement that disentangles sources of magnetic and nonmagnetic decoherence in graphene. Magnetic defects are shown to be the primary cause of spin relaxation, masking any potential effects of spin-orbit interaction.

Real-time imaging of K atoms on graphite: interactions and diffusion.

Scanning tunneling microscopy (STM) at liquid helium temperature is used to image potassium adsorbed on graphite at low coverage (≈0.02 monolayer). Single atoms appear as protrusions on STM topographs. A statistical analysis of the position of the atoms demonstrates repulsion between adsorbates, which is quantified by comparison with molecular dynamics simulations. This gives access to the dipole moment of a single adsorbate, found to be 10.5±1 D. Time-lapse imaging shows that long-range order is broken by thermally activated diffusion, with a 30 meV barrier to hopping between graphite lattice sites.