Noncentrosymmetric and Chiral 2D Quantum Materials Through Screw Dislocations and Structural Tuning

Rationally controlling the structures of two-dimensional (2D) layered materials allows us to tune the electronic structures and quantum states of matter, discover new physical properties, thus enable new applications. We show how the phase, layer stacking and thus physical properties of 2D MX₂ materials can be influenced by screw dislocations. Noncentrymmetry of these MX₂ materials and 2D Ruddlesden-Popper (RP) lead halide perovskites could be enabled at the monolayer and bulk crystal structure level by structural tuning and screw dislocations. Furthermore, chiral microplates of MX₂ and 2D RP perovskites can be produced via a screw dislocation growth mechanism and the resulting chiroptical properties of individual chiral objects are studied using fluorescence detected circular dichroism (FDCD) microscopy and other polarized spectroscopic/nonlinear optical techniques. Moreover, we achieved systematic interlayer twisting of MX₂ spiral layers grown via screw dislocations due to mismatched geometry between Euclidean crystal lattices and non-Euclidean (curved) surfaces to form moiré superlattices, which could lead to novel quantum phenomena. The ability to enable and control noncentrosymmetry, chirality, and twisting of 2D materials open up new dimensions of quantum materials for the study of nonlinear and chiral optical properties, valleytronics and twistronics.