In a paper recently published in Nature Communications, an international team, led by Prof. Kian Ping Loh, The Hong Kong Polytechnic University (PolyU) and National University of Singapore(NUS), for the experimental part and by Dr. Alessandro Stroppa, CNR-SPIN, for the theoretical part, demonstrates, for the first kind, the coexistence of chirality, electric and magnetic orders in a hybrid organic-inorganic perovskite (R/S)-(MPA)2CuCl4 (MPA = β-methylphenethylamine).
An object is chiral if it cannot be superimposed on its mirror image, by any rigid motion of the first time, i.e., translation or proper rotation. This implies that the object does not have any improper symmetry operation, Sn, i.e., neither inversion (S_1), nor mirror (S_2) nor roto-reflection symmetry.
Chiral multiferroics offer remarkable capabilities for controlling quantum devices at multiple levels. However, these materials are rare due to the competing requirements of long-range orders and strict symmetry constraints, imposed by chirality.
By employing Landau symmetry mode analysis, the team introduces a new symmetry mode-based chiral order parameter and investigates the interplay between chirality and ferroic orders, thus proposing a novel mechanism for chirality transfer in hybrid systems. This mechanism involves the coupling of two non-chiral distortions via a new pseudo-scalar order parameter,
where 
represents the ferroelectric momentand 
denotest the ferro-rotational moment of the metal-halide bond-tilt patterm.This order parameter distinguishes crystal handedness, i.e., it differentiates between (R)- and (S)-enantiomer based on its sign. Moreover, the reversal of this descriptor’s sign can be associated with coordinated transitions in ferroelectric distortions, Jahn-Teller antiferro-distortions, and Dzyaloshinskii-Moriya vectors, indicating the mediating role of crystallographic chirality in magnetoelectric correlations.
The project has been partially supported by the Italian Ministry of Research under the PRIN 2022 Grant No 2022F2K7J5 - “Two-dimensional chiral hybrid organic–inorganic perovskites for chiroptoelectronics” PE 3 funded by PNRR Mission 4 Istruzione e Ricerca - Component C2 - Investimento 1.1, Fondo per il Programma Nazionale di Ricerca e Progetti di Rilevante Interesse Nazionale PRIN 2022 – CUP B53D23004130006.
