Quasi-two-dimensional electron and hole gases at the head-to-head and tail-to-tail 180^o domain walls in ferroelectric thin films

Many schemes on screening of bound charges and stabilization of head-to-head (HH) and tail-to-tail (TT) 180^o domain walls (DWs) in ferroelectrics have been proposed. Some studies have employed (i) substitutional atoms at one or two HH and TT domain walls in superlattices, (ii) altering defect concentration at the tails in thin films. However, such approaches say nothing regarding the intrinsic critical thickness for the stabilization of the 2D conducting layers for screening of polarization charges, the spatial extend in which the hole and electron gases cover nor the magnitude extend of polarization if the said domain walls would be induced in a slab.
By ab initio means, we show stabilization of such DWs in PbTiO₃ thin films by electrostatic screening from free carriers [1].
Our findings support the existence of an extra source of charge at the domain walls to explain the enhancement of the conductivity observed in some domains walls of perovskite oxides.