  It has been found previously that the presence or absence of topological edge
states in the Su-Schrieffer-Heeger (SSH) model has a huge impact on harmonic
generation spectra. More specifically, the yield of harmonics for harmonic
orders that correspond to photon energies below the band gap is many orders of
magnitude different in the trivial and topological phase. It is shown in this
work that this effect is still present if electron-electron interaction is
taken into account, i.e., if a Hubbard term is added to the SSH Hamiltonian. To
that end, finite SSH-Hubbard chains at half filling are considered that are
short enough to be accessible to exact diagonalization but already showing edge
states in the topological phase. We show that the huge difference in the
harmonic yield between the trivial and the topological phase can be reproduced
with few-level models employing only the many-body ground state and a few
excited many-body states.
