Optical transitions between Landau levels: AA-stacked bilayer graphene

TL;DR

This paper investigates the low-frequency optical excitations in AA-stacked bilayer graphene using a tight-binding model, revealing unique absorption peaks and their dependence on magnetic field strength and Fermi level, with comparisons to AB-stacked graphene.

Contribution

It provides a detailed analysis of optical transitions and selection rules in AA-stacked bilayer graphene, highlighting the influence of stacking symmetry on optical properties.

Findings

Two groups of asymmetric Landau levels lead to distinct absorption peaks.

Absorption peaks follow monolayer-like selection rules.

Optical properties differ significantly between AA- and AB-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.