Nonlinear Phononics in Hybrid Lead Halide Perovskites

The microscopic origin of the surprising performance of hybrid lead halide perovskite (LHP) semiconductors for optoelectronic devices is still under debate. It has been suggested that their highly polarizable and anharmonic lattice might beneficially govern their optoelectronic properties in the form of dynamic charge carrier screening. To study the LHP’s ultrafast lattice response when subjected to a transient electric field, we employ intense, close to single-cycle, THz fields exceeding 1.5 MV/cm. By probing the THz induced Kerr effect, we witness the nonlinear excitation of coherent phonons of the inorganic cage in CsPbBr₃ and in the hybrid MAPbBr₃ in their low-temperature orthorhombic phase. We discuss different possible nonlinear photonic and phononic excitation pathways and their implications on dynamic charge carrier screening. Identifying the dominating polarizable and/or anharmonic phonon modes might unveil a fundamental mechanism how lattice dynamics enable charge carrier protection, even in more exotic electronic phases.