C.P. Chang

Magneto-optical selection rules in bilayer Bernal graphene

The low-frequency magneto-optical properties of bilayer Bernal graphene are studied by the tight-binding model with the four most important interlayer interactions taken into account. Since the main features of the wave functions are well-depicted, the Landau levels can be divided into two groups based on the characteristics of the wave functions. These Landau levels lead to four categories of absorption peaks in the optical absorption spectra. Such absorption peaks own complex optical selection rules, and these rules can be reasonably explained by the characteristics of the wave functions. In addition, twin-peak structures, regular frequency-dependent absorption rates, and complex field-dependent frequencies are also obtained in this work. The main features of the absorption peaks are very different from those in monolayer graphene and have their origin in the interlayer interactions.

Effects of Transverse Electric Fields on Quasi-Landau Levels in Zigzag Graphene Nanoribbons

The magnetoelectronic properties of one-dimensional zigzag graphene nanoribbons are investigated using the Peierls tight-binding model with uniform magnetic and electric fields. They are mainly determined by external fields and quantum confinement effects. Magnetic fields lead to quasi-Landau levels (QLLs), enhance partial flat bands, and result in Landau wave functions. Electric fields significantly distort dispersionless QLLs, change the band symmetry, induce more band-edge states, split partial flat bands, and drastically alter the distribution of wave functions. The density of states directly reflects the main features of energy bands, such as the numbers, frequencies, heights, and divergence forms of prominent peaks, which can be confirmed experimentally. Magneto-optical absorption spectra are predicted to be markedly changed under the influence of external electric fields.

Electronic and optical properties in graphane

We develop the tight-binding model to study electronic and optical properties of graphane. The strong chemical bondings among the carbon and hydrogen atoms induce a special band structure and thus lead to the rich optical excitations. The absorption spectrum hardly depends on the direction of electric polarization. It exhibits a lot of shoulder structures and absorption peaks, which arise from the extreme points and the saddle points of the parabolic bands, respectively. The threshold optical excitations, only associated with the and orbitals of the carbon atoms, are revealed in a shoulder structure at 3.5 eV. The first symmetric absorption peak, appearing at 11 eV, corresponds to energy bands due to the considerable hybridization of carbon orbitals and H 1s orbitals. Also, some absorption peaks at higher frequencies indicate the bonding of and orbitals. These results are in sharp contrast to those of the graphene systems.