  In frequently studied two-band models for solid-state high-harmonic
generation, interband harmonics in principle can range from the minimum to the
maximum bandgap. However, it is known that a laser-intensity dependent cutoff
exists that may be well below the maximum bandgap unless the laser intensity is
so high that the electrons explore the entire Brillouin zone. We show that this
laser-intensity dependent cutoff is formed by destructive interference of the
emission of electrons starting at different initial states in the Brillouin
zone. The calculations in this work are for Su-Schrieffer-Heeger chains but our
findings apply to other two-band systems as well. Only when the sampling of the
Brillouin zone is fine enough or, equivalently, a finite chain is long enough
in position space, the destructive interference is complete and forms the
cutoff. For coarser sampling and shorter chains all harmonics between minimum
and maximum bandgap are emitted. A time-frequency analysis shows how certain
trajectories are responsible for the formation of the cutoff.
