Metal–ferroelectric supercrystals with periodically curved metallic layers

Simultaneous manipulation of multiple boundary conditions in nanoscale heterostructures offers a versatile route to stabilizing unusual structures and emergent phases. Here, we show that a stable supercrystal phase comprising a three-dimensional ordering of nanoscale domains with tailored periodicities can be engineered in PbTiO 3 –SrRuO 3 ferroelectric–metal superlattices. A combination of laboratory and synchrotron X-ray diffraction, piezoresponse force microscopy, scanning transmission electron microscopy and phase-field simulations reveals a complex hierarchical domain structure that forms to minimize the elastic and electrostatic energy. Large local deformations of the ferroelectric lattice are accommodated by periodic lattice modulations of the metallic SrRuO 3 layers with curvatures up to 10 7 m −1 . Our results show that multidomain ferroelectric systems can be exploited as versatile templates to induce large curvatures in correlated materials, and present a route for engineering correlated materials with modulated structural and electronic properties that can be controlled using electric fields. Ferroelectric superlattices can present a rich variety of phenomena. Here, in PbTiO 3 /SrRuO 3 superlattices, it is shown that a complex and stable hierarchical supercrystal can form, with the correlated metal of the SrRuO 3 layers showing large curvatures.