Nature 433, 395–399 (2005).

It has been drawn to our attention that in our Letter we may have inadvertently underplayed the significance of an earlier experimental study (ref. 11) through an unfortunate choice of wording. Our intention was not to claim the first experimental realization of asymmetric properties in a three-component superlattice (ref. 11 claimed a similar realization), but the first experimental observation of strain-enhanced ferroelectric polarization in such structures.