Lead halide perovskites (LHPs) constitute a vast and highly diverse library of energy materials, which can be tailored by their organic cation composition, halide alloying, dimensionality, or chiral ligands to the specific needs of contemporary optoelectronic devices. So far, to optimize material properties, the material science community mainly focused on changing the static design of the perovskite lattice by tuning the chemical composition or morphology. Meanwhile, the full potential for dynamic phonon-driven ultrafast material control, as successfully applied for oxide perovskites, has not been exploited yet.

The advent of high-field terahertz (THz) sources enabled coherent control of fundamental low energy excitations, such as phonons. Recently, nonlinear driving schemes have extend these methods of contemporary IR-spectroscopy even to non-IR-active modes. Here, we employ these driving schemes to obtain coherent control over LHP lattice modes via the THz-induced Kerr effect (TKE). In 3D bulk LHPs, we find the TKE to be dominated by coherent octahedral twist modes, which are coupled to the electronic bandgap and the strong nonlinear THz polarizability [1]. After establishing coherent lattice control in lead bromides APbBr3 with either purely inorganic (A=Cs) or organic (A=MA, Methylammonium) A-site cations, we move to more complex stoichiometries hosting up to four cation species (Cs, MA, Guanidinium, and Formamidinium). For a specific mixing ratio of four cations, we counterintuitively find that the lattice coherence is restored and even doubled in time compared to the MAPbBr3 parent compound [2]. These dynamic lattice properties are accompanied by a stabilization of the cubic phase down to 80 K, higher photoluminescence, increased electron mobility, and thus indicate a delicate interplay of the static and dynamic lattice contributions to optoelectronic performance.

To investigate the impact of confinement and dimensionality of these lattice dynamics and their coherences, we extend our studies to 2D-layered Ruddlesden-Popper (PEA)₂MA_n-1PbnI_3n+1 compounds with n=1,2,3 inorganic octahedra layers forming periodic multiple quantum wells, separated by phenethylamine (PEA) organic spacer molecules [3]. Already at room temperature, we strikingly witness enhanced lattice coherences with a clear dependence on the degree of confinement. By the mode-selective azimuthal symmetry of the TKE, we identify simultaneous IR- and Raman-activity of specific inorganic cage modes, representing fingerprints of hidden inversion symmetry breaking despite the globally centrosymmetric crystal structure [3]. This transient or local breaking of inversion symmetry might contribute to previous indications of the Rashba-Dresselhaus effect, paving the way for spintronic applications in quasi-2D LHPs. Eventually, we further reduce the dimensionality to chain-like (1D) hybrid metal halide structures given by α-Ethylbenzylamine lead bromide compounds, which additionally open our studies to chiral properties.