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 graphene's 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.

Pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism. Theoretically, the π magnetism induced by the monovacancy in graphene is characteristic of two spin-split density-of-states (DOS) peaks close to the Dirac point. Since its prediction, many experiments have attempted to study this π magnetism in graphene, whereas only a notable resonance peak has been observed around the atomic defects, leaving the π magnetism experimentally elusive. Here, we report direct experimental evidence of π magnetism by using a scanning tunneling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens of meV. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. Unexpectedly, the effective g factor around the atomic defect is measured to be about 40, which is about 20 times larger than the g factor for electron spins.

Theoretical research has predicted that ripple of graphene generates effective gauge field on its low energy electronic structure and could lead to Landau quantization. Here we demonstrate, using a combination of scanning tunneling microscopy and tight-binding approximation, that Landau levels will form when effective pseudomagnetic flux per ripple Φ ~ (h 2 /la)Φ 0 is larger than the flux quantum Φ 0 (here h is the height, l is the width of the ripple, a is the nearest C-C bond length). The strain induced gauge field in the ripple only results in one-dimensional (1D) Landau-level quantization along the ripple. Such 1D Landau quantization does not exist in two-dimensional systems in an external magnetic field. Its existence offers a unique opportunity to realize novel electronic properties in strained graphene.

In strained graphene, lattice deformation can create pseudo-magnetic fields and result in zero-field Landau level-like quantization. In the presence of an external magnetic field, valleypolarized Landau levels are predicted to be observed because the pseudo-magnetic fields are of opposite directions in the K and K′ valleys of graphene. Here, we present experimental spectroscopic measurements by scanning tunneling microscopy of strained graphene on Rh foil.We direct observed valley splitting of the Landau level induced by the coexistence of the pseudo-magnetic fields and external magnetic fields. The observed result paves the way to exploit novel electronic properties in graphene through the combination of the pseudo-magnetic fields and the external magnetic fields. One Sentence Summary:Valley-polarized Landau quantization is realized in strained graphene via combination of pseudo-magnetic fields and external magnetic fields. Main Text:The linear band dispersion of graphene allows the existence of a variety of mechanisms which generate effective gauge fields in the low-energy electronic theory (1-4).Very recently, it has been demonstrated explicitly that a spatially varying lattice distortion in

Here, we report a facile method to generate a high density of atomic-scale defects in graphene on metal foil and show how these defects affect the electronic structures of graphene layers. Our scanning tunneling microscope measurements, complemented by first-principles calculations, reveal that the atomic-scale defects result in both the intervalley and intravalley scattering of graphene. The Fermi velocity is reduced in the vicinity area of the defect due to the enhanced scattering.