A Mathematical Double‐Matrix Switchable Homochiral Ferroelectric

Homochiral ferroelectrics have attracted increasing attention in recent years because of their distinctive chiroptical effects in contrast to ordinary ferroelectrics. Moreover, they provide a great opportunity to show mathematically switchable matrix elements between non‐zero and zero values in both second‐order nonlinear optical susceptibility χ(2) and piezoelectric d matrices to realize the dual on/off switching of second‐harmonic generation circular dichroism (SHG‐CD) and piezoelectric responses, which, however, has never been reported. Herein, for the first time, we reported homochiral metal halide ferroelectrics (R‐/S‐BTA)2CdBr4 (BTA = 3‐bromo‐2‐hydroxypropyltrimethylammonium), which exhibits a 432F2 ferroelectric phase transition at 362 K, accompanied by the switchable matrix elements between non‐zero (for point group 2) and zero (for point group 432) values in both χ(2) and d matrices. They show strong SHG‐CD effects with an anisotropy factor up to 1.28, far exceeding that of other chiral ferroelectrics. Notably, the 432F2 phase transition enables (R‐/S‐BTA)2CdBr4 to show the unprecedented dual on/off switching of SHG‐CD and piezoelectric response between the SHG‐CD/piezoelectric active state in the ferroelectric phase and SHG‐CD/piezoelectric inactive state in the paraelectric phase. Our findings shed light on the exploration of mathematical double‐matrix switchable chiral ferroelectrics with SHG‐CD and piezoelectric response switching.