Fig. 4: Rashba splitting revealed by two-photon photoluminescence excitation (TP-PLE) on exfoliated ferroelectric (BA)2(MA)Pb2Br7 (nā=ā2) film with and without striped domains.

a One-photon PL emission spectrum acquired on the surface of nā=ā2 Br-RPP film. b TP-PLE spectra of nā=ā2 Br-RPP film in three different regions: a domain-free area, domain A and domain B, as indicated by the respective inlet images. The positions of the exciton energy (EX), Rashba splitting energy (4ER) and energy of maximum PL intensity (EMax) are designated on the spectra.