Charge-order-induced directional enhancement of non-diagonal second-order nonlinear optical tensor components

Abstract

Selective enhancement of non-diagonal second-order NLO tensor components remains largely unexplored. Here, we demonstrate that charge ordering in mixed-valence ions enables chemical tuning of this effect in low-symmetry, non-centrosymmetric crystals. Using Ag₂BiO₃, calculations reveal that periodic Bi³⁺/Bi⁵⁺ ordering prevents local inversion symmetry and enhances non-diagonal tensors. Disrupting this ordering reduces d₂₄, establishing a design principle for photonic applications.