  We design and analyze photo-metamaterials with each meta-atom containing both
photodiode and light-emitting diode. Illumination of the photodiode by the
light-emitting diode gives rise to an additional optical feedback within each
unit cell, which strongly affects resonant properties and nonlinear response of
the meta-atom. In particular, we demonstrate that symmetry breaking occurs upon
a certain threshold magnitude of the incident wave intensity resulting in an
abrupt emergence of second-harmonic generation, which was not originally
available, as well as in the reduced third-harmonic signal.
