Si-Yu Li

Scanning Tunneling Microscopy of the .PI. Magnetism of a Single Carbon Vacancy in Graphene

The pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism with local magnetic moments ~ 1.5 per vacancy1-6. Theoretically, both the electrons and electrons of graphene contribute to the magnetic moment of the defects, and the pi magnetism is characterizing of two spin-split DOS (density-of-states) peaks close to the Dirac point1,6. Since its prediction, many experiments attempt to study this pi magnetism in graphene, whereas, only a notable resonance peak has been observed around the atomic defects6-9, leaving the pi magnetism experimentally so elusive. Here, we report direct experimental evidence of the pi magnetism by using scanning tunnelling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens meV and the two spin-polarized states degenerate into a profound peak at positions with distance of ~ 1 nm away from the monovacancy. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. The effective g-factors geff around the atomic defect is measured to be about 40. Such a giant enhancement of the g-factor is attributed to the strong spin polarization of electron density and large electron-electron interactions near the atomic vacancy.

Detecting giant electron-hole asymmetry in a graphene monolayer generated by strain and charged-defect scattering via Landau level spectroscopy

The electron-hole symmetry in graphene monolayer, which is analogous to the inherent symmetric structure between electrons and positrons of the Universe, plays a crucial role in the chirality and chiral tunneling of massless Dirac fermions. Here we demonstrate that both strain and charged-defect scattering could break this symmetry dramatically in a graphene monolayer. In our experiment, the Fermi velocities of electrons

Energy gaps of atomically precise armchair graphene sidewall nanoribbons

{v}_{F}^{e}

Experimental observation of surface states and Landau levels bending in bilayer graphene

and holes

Spatially resolving unconventional interface Landau quantization in a graphene monolayer-bilayer planar junction

{v}_{F}^{h}

Wide-band-gap wrinkled nanoribbon-like structures in a continuous metallic graphene sheet

are measured directly through Landau level spectroscopy. In strained graphene with lattice deformation and curvature, the

Observation of unconventional splitting of Landau levels in strained graphene

{v}_{F}^{e}

Landau quantization of Dirac fermions in graphene and its multilayers

and

Splitting of Van Hove singularities in slightly twisted bilayer graphene

{v}_{F}^{h}

Magnetic-field-controlled negative differential conductance in scanning tunneling spectroscopy of graphene npn junction resonators

are measured as