Exciton dynamics, lifetimes and scattering are directly related to the exciton dispersion, or bandstructure. While electron and phonon bandstructures are well understood and can be easily calculated from first principles, the exciton bandstructure is commonly conflated with the underlying electronic bandstructure, where the exciton dispersion is assumed to follow the same dispersion as the electron and hole bands from which it is composed (i.e., the effective mass model). Here, we present a general theory of exciton bandstructure within both ab initio and model Hamiltonian approaches. We show that contrary to common assumption, the exciton bandstructure contains non-analytical discontinuities -- a feature which is impossible to obtain from the electronic bandstructure alone. These discontinuities are purely quantum phenomena, arising from the exchange scattering of electron-hole pairs. We show that the degree of these discontinuities depends on materials' symmetry and dimensionality, with jump discontinuities occurring in 3D and different orders of removable discontinuities in 2D and 1D. We connect these unexpected features to the early stages of exciton dynamics, which shows remarkable correspondence with recent experimental observations and suggests that the measured diffusion patterns are influenced by the underlying exciton bandstructure.
Two-dimensional (2D) monolayer phosphorene, a 2D system with quasi-one-dimensional (quasi-1D) excitons, provides a unique 2D platform for investigating the dynamics of excitons in reduced dimensions and fundamental many-body interactions. However, on the other hand, the quasi-1D excitonic nature can limit the luminescence quantum yield significantly. Here, we report exciton brightening in monolayer phosphorene achieved via the dimensionality modification of excitons from quasi-1D to zero-dimensional (0D), through the transference of monolayer phosphorene samples onto defect-rich oxide substrat…
With the example of hexagonal boron nitride, we demonstrate how the character of electron-hole (e-h) pairs in van der Waals bound low-dimensional systems is driven by layer stacking. Four types of excitons appear, with either a two- or three-dimensional spatial extension. Electron and hole distributions are either overlapping or exhibit a charge-transfer nature. We discuss under which structural and symmetry conditions they appear and they are either dark or bright. This analysis provides the key elements to identify, predict, and possibly tailor the character of e-h pairs in van der Waals mat…
Dimensionality-Dependent Exciton Dispersion in a Single-Band Mott Insulator
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；School of Physics, Zhejiang University（浙江大学物理学院）；State Key Laboratory of Silicon and Advanced Semiconductor Materials, Zhejiang University（浙江大学硅酸盐先进半导体材料国家重点实验室）；School of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices, Renmin University of China（中国人民大学物理学院及光电功能材料与微纳器件北京市重点实验室）；Key Laboratory of Quantum State Construction and Manipulation (Ministry of Education), Renmin University of China（中国人民大学量子态构建与操控教育部重点实验室）；International Center for Quantum Materials, and Electron Microscopy Laboratory, School of Physics, Peking University（北京大学物理学院国际量子材料中心及电子显微镜实验室）；Department of Physics, Fuzhou University（福州大学物理系）
The tunability of the bandgap, absorption and emission energies, photoluminescence (PL) quantum yield, exciton transport, and energy transfer in transition metal dichalcogenide (TMD) monolayers provides a new class of functions for a wide range of ultrathin photonic devices. Recent strain-engineering approaches have enabled us to tune some of these properties, yet dynamic control at the nanoscale with real-time and -space characterizations remains a challenge. Here, we demonstrate a dynamic nano-mechanical strain-engineering of naturally-formed wrinkles in a WSe2 monolayer, with real-time inve…
The interplay between dimensionality and anisotropicity leads to intriguing optoelectronic properties and exciton dynamics in low dimensional semiconductors. In this study we use nanostructured phosphorene as a prototypical example to unfold such complex physics and develop a general first-principles framework to study exciton dynamics in low dimensional systems. Specifically we derived the radiative lifetime and light emission intensity from 2D to 0D systems based on many-body perturbation theory, and investigated the dimensionality and anisotropicity effects on radiative recombination lifeti…
Engineering Excitons through Polymorphism and Dimensional Confinement in Low-Dimensional Tellurium
Federal University of Goi\'as, Institute of Physics, Campus Samambaia, 74960600 Goi\ ania, Brazil；Institute of Physics, Computational Materials Laboratory, University of Bras \' i lia, Bras \' i lia, 70910-900, Brazil
Layered van der Waals (vdW) magnetic materials have attracted significant research interest to date. In this work, we employ the first-principles many-body perturbation theory to calculate excited-state properties of a prototype vdW magnet, chromium trichloride (CrCl3), covering monolayer, bilayer, and bulk structures. Unlike usual non-magnetic vdW semiconductors, in which many-electron interactions and excited states are sensitive to dimensionality, many-electron interactions are always enhanced and dominate quasiparticle energies and optical responses of both two-dimensional and bulk CrCl3. …
Twisted light carries a well-defined orbital angular momentum (OAM) per photon. The quantum number l of its OAM can be arbitrarily set, making it an excellent light source to realize high-dimensional quantum entanglement and ultra-wide bandwidth optical communication structures. To develop solid-state optoelectronic systems compatible with such promising light sources, a timely challenging task is to efficiently and coherently transfer the optical OAM of light to certain solid-state optoelectronic materials. Among the state-of-the-art emergent materials, atomically thin monolayer transition me…
