Optical transitions between Landau levels: AA-stacked bilayer graphene

Abstract

The low-frequency optical excitations of AA-stacked bilayer graphene are investigated by the tight-binding model. Two groups of asymmetric LLs lead to two kinds of absorption peaks resulting from only intragroup excitations. Each absorption peak obeys a single selection rule similar to that of monolayer graphene. The excitation channel of each peak is changed as the field strength approaches a critical strength. This alteration of the excitation channel is strongly related to the setting of the Fermi level. The peculiar optical properties can be attributed to the characteristics of the LL wave functions of the two LL groups. A detailed comparison of optical properties between AA-stacked and AB-stacked bilayer graphenes is also offered. The compared results demonstrate that the optical properties are strongly dominated by the stacking symmetry. Furthermore, the presented results may be used to discriminate AABG from MG, which can be hardly done by STM

Configuration-enriched magneto-electronic spectra of AAB-stacked trilayer graphene

“…The former and the latter have, respectively, two pairs of linear and parabolic bands. The two isotropic Dirac-cones in the AA-stacked system are magnetically quantized into two groups of LLs with monolayer-like wavefunctions and energy spectrum [76]. Also, the AB-stacked system presents two groups of LLs, with each LL having a single-mode wavefunction in the absence of LL anticrossing [77].…”

Metal-insulator transition and phase separation in doped AA-stacked graphene bilayer

“…If ∆ 0 is small, the value of |µ ′ | ∼ ∆ 0 is also small, and we can omit Θ-functions in the first terms in Eqs. (11) and (12). From these, we derive…”

“…Further, we will demonstrate that the required levels of doping are within current experimental capabilities. Unlike AB-stacked bilayers, the AA-BLG received very modest theoretical attention [8][9][10][11][12][13]. However, advances in fabrication of AA-stacked bilayers and multilayers [7,8] underscore the need for thorough theoretical investigations.…”

“…(11) and Θ-functions by the Fermi distributions in Eq. (12), [f (ε) is the Fermi distribution function]. Then, we derive µ = µ(x, T ) as a function of doping and temperature.…”

Introduction

“…The low-energy band structure consists of several monolayerlike massless Dirac cones [78][79][80]153], which are exactly located at the two valleys K and K′, while the energies of the Dirac points shift away from the Fermi energy due to the vertically projected geometry. The absorption spectrum is, in general, a superposition of monolayer-like spectra, because only the vertical excitations of intra-Dirac-cones are permitted, regardless of the external electric and magnetic fields [153,183]. However, the stacking effect gives rise to an optical gap for the even-layer configurations, which is a forbidden optical transition zone resulting from free carriers in the Dirac cones.…”