Ke-Ke Bai

Creating one-dimensional nanoscale periodic ripples in a continuous mosaic graphene monolayer.

In previous studies, it has proved difficult to realize periodic graphene ripples with wavelengths of a few nanometers. Here we show that one-dimensional (1D) periodic graphene ripples with wavelengths from 2 nm to tens of nanometers can be implemented in the intrinsic areas of a continuous mosaic (locally N-doped) graphene monolayer by simultaneously using both the thermal strain engineering and the anisotropic surface stress of the Cu substrate. Our result indicates that the constraint imposed at the boundaries between the intrinsic and the N-doped regions play a vital role in creating these 1D ripples. We also demonstrate that the observed rippling modes are beyond the descriptions of continuum mechanics due to the decoupling of graphenes bending and tensional deformations. Scanning tunneling spectroscopy measurements indicate that the nanorippling generates a periodic electronic superlattice and opens a zero-energy gap of about 130 meV in graphene. This result may pave a facile way for tailoring the structures and electronic properties of graphene.

Strain-induced one-dimensional Landau level quantization in corrugated graphene

Theoretical research has predicted that ripples of graphene generates effective gauge field on its low energy electronic structure and could lead to zero-energy flat bands, which are the analog of Landau levels in real magnetic fields. Here we demonstrate, using a combination of scanning tunneling microscopy and tight-binding approximation, that the zero-energy Landau levels with vanishing Fermi velocities will form when the effective pseudomagnetic flux per ripple is larger than the flux quantum. Our analysis indicates that the effective gauge field of the ripples results in zero-energy flat bands in one direction but not in another. The Fermi velocities in the perpendicular direction of the ripples are not renormalized at all. The condition to generate the ripples is also discussed according to classical thin-film elasticity theory.

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

Electronic structures of graphene layers on a metal foil: The effect of atomic-scale defects

{v}_{F}^{e}

Direct probing of the stacking order and electronic spectrum of rhombohedral trilayer graphene with scanning tunneling microscopy

and holes

Massless Dirac fermions trapping in a quasi-one-dimensional npn junction of a continuous graphene monolayer

{v}_{F}^{h}

Generating atomically sharp p−n junctions in graphene and testing quantum electron optics on the nanoscale

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

Modulating the Electronic Properties of Graphene by Self-Organized Sulfur Identical Nanoclusters and Atomic Superlattices Confined at an Interface

{v}_{F}^{e}

Observation of unconventional splitting of Landau levels in strained graphene

and