Physics

The low-frequency magneto-optical absorption spectra of bilayer Bernal graphene are studied within the tight-binding model and gradient approximation. The interlayer interactions strongly affect the electronic properties of the Landau levels (LL's), and thus enrich the optical absorption spectra. According to the characteristics of the wave functions, the low-energy LL's can be divided into two groups. This division results in four kinds of optical absorption peaks with complex optical selection rules. Observing the experimental convergent absorption frequencies close to zero magnetic field might be useful and reliable in determining the values of several hopping integrals. The dependence of the optical absorption spectra on the field strength is investigated in detail, and the results differ considerably from those of monolayer graphene.

The low-frequency magneto-optical properties of bilayer Bernal graphene are studied by the tight-binding model with 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.

Magneto-electronic structures of AB-stacked bulk graphite are investigated by the Peierls tight-binding model, which takes account of all interlayer interactions and field-induced Peierls phases simultaneously. This model is feasible for all π electronic states and capable of drawing the analytic solution for state wave functions. The external magnetic field B0z condenses the planar motion of electrons into Landau levels, and the coupling between layers causes these levels to oscillate along kz. The band edge states are mainly located at the Brillouin zone boundaries, where their frequencies as a function of field are closely related to the atomic hopping integrals. Landau levels are divided into two groups based on the wave function distribution. Besides, wave functions undergo a particular transition between atomic sites in response to kz. From the behavior of energies and wave functions, we can infer the monolayer-like plus bilayer-like features in bulk graphite. The explicit characterization of Landau levels in this work could be applied to clarify and elucidate the experimental measurements on graphene layers.

The low-frequency magneto-absorption spectra of monolayer and bilayer graphene are evaluated within the gradient approximation. On the basis of Peierls tight-binding model, we can draw the wave function distribution over its sublattices and bring them into the calculation of optical spectra. The optical selection rules and the absorption rate can be accurately determined. The interlayer interactions in bilayers effectively alter the Landau level structures and thus the absorption spectra, such as the field dependence of absorption lines and the appearance of double-peaked absorptions.

The magneto-absorption spectra are calculated for the AA- stacked bilayer graphene. Two groups of Landau levels with different symmetry in wave function are found to coexist in the low energy region. The optical transitions between the two groups give rise to two kinds of absorption peaks. The wave- function distribution can clearly characterize individual Landau levels, and further determine the optical selection rules and absorption rates. The AA bilayer has quite different spectral features compared to the AB bilayer and monolayer, as a result from the interlayer interactions and stacking symmetry. Only a single absorption survives below certain critical frequency, while other peaks are paired together and sequentially emerged above this critical energy. With a continuous change in field strength, the excitation channels are switched, associated with the abrupt changes in their frequency.

The Peierl's tight-binding model, with the band Hamiltonian matrix, is used to calculate the magnetoelectronic structure of a monolayergraphite. There are many flat Landau levels and some oscillatory Landau levels. The low Landau-level energies are characterized by a simple relation, not for others. State degeneracy is, respectively, fourfold degenerate and doubly degenerate at low and high energies. The level spacing

The diverse structural and electronic properties of the Si-adsorbed and -substituted monolayer graphene systems are studied by a complete theoretical framework under the first-principles calculations, including the adatom-diversified geometric structures, the Si- and C-dominated energy bands, the spatial charge densities, variations in the spatial charge densities and the atom- and orbital-projected density of states (DOSs). These critical physical quantities are unified together to display a distinct physical and chemical picture in the studying systems. Under the Si-adsorption and Si-substitution effects, the planar geometric structures are still remained mainly owing to the very strong C–C and Si–C bonds on the honeycomb lattices, respectively. The Si-adsorption cases can create free carriers, while the finite- or zero-gap semiconducting behaviors are revealed in various Si-substitution configurations. The developed theoretical framework can be fully generalized to other emergent...