| Abstract Scope |
Integrating two-dimensional (2D) materials have widened the spectrum of building blocks for creating hybrid heterostructure systems with unique functionalities and excellent performance. 2D metal halide perovskites are highly attractive as promising candidates for polarization-active chiral materials because their quantum-well-like structure, strong exciton binding energy, and dielectric confinement lead to unique optical properties. The intriguing electronic structure of 2D topological semimetals, representing a novel class of condensed matter, is of fundamental interest because of their exotic quantum nature and potential quantum device applications. Here, we report our recent findings on 2D Weyl-semimetal (WSM) states achieved by a thickness-dependent Dirac- to Weyl-semimetal phase transition in Bi0.96Sb0.04 thin films. The 2D WSM states show novel photo-transport of charge carriers such as topological Lifshitz transition, revealed by a thickness-dependent plasma frequency, and circular photogalvanic effect (CPGE), which are discussed based on the theoretical expectations. We also report unprecedently-high luminescence dissymmetry factor (0.3) at room temperature for single-crystalline 2D (PEA)2PbI4 perovskites. This unusually-strong circularly-polarized photoluminescence (PL) is accompanied by pronounced angular dependence of linearly-polarized PL and photocurrent anisotropy under circularly-polarized excitation, indicating CPGE (nA). |