  The moir\'e of twisted graphene bilayers can generate flat bands in which
charge carriers do not posses enough kinetic energy to escape Coulomb
interactions with each other leading to the formation of novel strongly
correlated electronic states. This exceptionally rich physics relies on the
precise arrangement between the layers.We survey published Scanning Tunnelling
Microscope (STM) measurements to prove that near the magic angle, native
heterostrain, the relative deformations between the layers, dominates twist in
determining the flat bands. This is demonstrated at large doping where
electronic correlations have a weak effect and where we also show that
tip-induced strain can have a strong influence. In the opposite situation of
low doping, we find that electronic correlation further normalize the flat
bands in a way that strongly depends on experimental details.

Mesoscale and Nanoscale Physics