  We reveal that strong flexoelectric effect of solids can be induced due to
the signfi?cant charge migration along the strain gradient direction, which
represents a new understanding of the origin of flexoelectricity. Beyond the
linear response theory, we illustrate such charge migration that is driven by
an electric field effect in bent silicon thinfilms. Due to such charge
migration, the variation of atomic charge no longer represents a linear
response to strain gradient and the resulting giant flexoelectric coeffcients
being size dependent cannot be treated as a bulk property. The obtained
flexoelectric coefficients compare well with the typical experimental values as
reported in various ceramics. Our results shed light on elucidating the
discrepancy between theory and experiment,and pave a new way to discover
excellent flexoelectric performance in conventional materials.
