  We present infrared transmission spectroscopy study of the inter-Landau-level
excitations in quasi-neutral epitaxial graphene nanoribbon arrays. We observed
a substantial deviation in energy of the $L_{0(-1)}$$\to$$L_{1(0)}$ transition
from the characteristic square root magnetic-field dependence of
two-dimensional graphene. This deviation arises from the formation of
upper-hybrid mode between the Landau level transition and the plasmon
resonance. In the quantum regime the hybrid mode exhibits a distinct dispersion
relation, markedly different from that expected for conventional
two-dimensional systems and highly doped graphene.
