Fig. 4.

Resonance profiles for (PbTiO₃)_n/(SrTiO₃)_n superlattices through the titanium L₃ edge at (A) q_lateral = +q_{χ_pair} for n = 14 and (B) q_lateral = +q_a-domain = +2π/d_a-domain for n = 4, where d_a-domain ∼ 70 nm. (Upper) The polarization-averaged diffraction intensity (red) for both X-ray helicities, and (Lower) XCD (green). Insets show planar view HR-STEM images of (A) an array of polar cores ordered along [100]_χ (horizontal scale bar: 50 nm) and (B) an array of ferroelectric a domains ordered along [110]_χ (horizontal scale bar: 200 nm). Superlattices with chiral polar arrays exhibit strong XCD in A that is characteristic of the chiral arrangement of electric polarization in the texture. In superlattices with smaller layer thickness, the polarization arranges into periodic a domains only, with no chiral structure and correspondingly negligible XCD.