– based heterostructure

The demand for ever-smaller devices has been approaching the fundamental limits of ultrathin ferroelectric films. In the low-thickness regime, maintaining a large, stable and switchable ferroelectric polarization relies on the control of the strain state, thickness, interface termination and electrostatic conditions. Achieving a robust polarization or a controlled domain state remains, however, challenging. Imperfect charge screening at interfaces results in non-cancellation of internal fields that can in extreme case annihilate ferroelectricity. Taking (BaTiO₃-SrRuO₃) capacitor-like heterostructures as a model system, we directly access the polarization and the domain state during the film deposition using optical second harmonic generation [1]. We observe a previously elusive impact of the evolving electrostatic environment on the BaTiO₃ domain state simultaneously with the growth. The initial phase of the top-electrode deposition is accompanied by temporary enhancement of built-in fields in the ferroelectric layer resulting in 180° domain formation. We discuss ways to manipulate the depolarizing field and control the polarization during the growth as it presents a possible route towards a novel class of oxide-electronic devices. [1] G. De Luca et al. (in press). Nat. Commun.