  Recent studies in high-harmonic spectroscopy of condensed matter mainly
focused on the bulk of the system under consideration. In this work, we
investigate the response of thin, hexagonal nanoribbons to an intense laser
pulse that is linearly polarized along the ribbon. Such nanoribbons are prime
examples of two-dimensional systems that are bulk-like in one direction and
finite in the other direction. Despite the atomically thin scale in the
direction perpendicular to the linearly polarized driving laser field, the
emitted harmonics are elliptically polarized if an alternating onsite potential
and Haldane hopping is taken into account. For given hoppings, we find a sudden
change of the helicity for a certain harmonic order. The origin of this flip is
traced back to phase differences between the components of Bloch states.
