  The generalized tight-binding model is developed to investigate the
feature-rich magneto-optical properties of AAB-stacked trilayer graphene. Three
intragroup and six intergroup inter-Landau-level (inter-LL) optical excitations
largely enrich the magneto-absorption peaks. In general, the former are much
higher than the latter, depending on the phases and amplitudes of LL
wavefunctions. The absorption spectra exhibit the single- or twin-peak
structures which are determined by the quantum modes, LL energy spectra and
Fermion distribution. The splitting LLs, with different localization centers
(2/6 and 4/6 positions in a unit cell), can generate very distinct absorption
spectra. There exist extra single peaks because of LL anticrosings. AAB, AAA,
ABA, and ABC stackings quite differ from one another in terms of the inter-LL
category, frequency, intensity, and structure of absorption peaks. The main
characteristics of LL wavefunctions and energy spectra and the Fermi-Dirac
function are responsible for the configuration-enriched magneto-optical
spectra.
