  The shift current is part of the second-order optical response of materials
with a close connection to topology. Here we report a sign inversion in the
band-edge shift photoconductivity of the Haldane model when the system
undergoes a topological phase transition. This result is obtained following two
complementary schemes. On one hand, we derive an analytical expression for the
band-edge shift current in a two-band tight-binding model showing that the sign
reversal is driven by the mass term. On the other hand, we perform a numerical
evaluation on a continuum version of the Haldane model. This approach allows us
to include off-diagonal matrix elements of the position operator, which are
discarded in tight-binding models but can contribute significantly to the shift
current. Explicit evaluation of the shift current shows that while the model
predictions remain accurate in the deep tight-binding regime, significant
deviations arise for shallow potential landscapes. Notably, the sign reversal
across the topological phase transition is observed in all regimes, implying it
is a robust effect that could be observable in a wide range of topological
insulators.
