Polar-discontinuity-induced stability of spontaneous polarization in ultrathin perovskite films

Abstract

The critical thickness for ferroelectricity arising from the depolarization field seriously hinders the progress of device miniaturization. Herein, we demonstrate that the polar-discontinuity-induced electronic reconstruction is capable to screen the depolarization field and stabilizes the polarization state in ultrathin ferroelectric films. In this work, the asymmetric Ba(Mg1/3Nb2/3)O3 (BMN) was inserted between the ferroelectric PbTiO3 (PTO) and the substrate SrTiO3 (STO) to create the polar discontinuity. First-principles calculations show that the two-dimensional electron gas (2DEG) and the two-dimensional hole gas (2DHG) are generated in the heterostructure PbTiO3/Ba(Mg1/3Nb2/3)O3/SrTiO3 (PTO/BMN/STO), which will screen the depolarization field. Consequently, the polarization value of PTO still maintains at 20 μC/cm2 (~25%) even when its thickness is only 1.5 unit cells. Moreover, the positions of the 2DEG and 2DHG, as well as the orientation of the spontaneous polarization, could be tuned by changing the configuration of BMN. The universality of this strategy in stabilizing spontaneous polarization is also confirmed in BaTiO3/Ba(Mg1/3Nb2/3)O3/SrTiO3 (BTO/BMN/STO) case. This work sheds a light on how to miniaturize the device with stable spontaneous polarization.