New Mechanism for Strongly Bound Excitons in Gapless Two-Dimensional Structures

Abstract

Common wisdom asserts that bound excitons cannot form in high-dimensional (d>1) metallic structures because of their overwhelming screening and unavoidable resonance with nearby continuous bands. Strikingly, here we illustrate that this prevalent assumption is not quite true. A key ingredient that has been overlooked is that of viable decoherence that thwarts the formation of resonances. As an example of this general mechanism, we focus on an experimentally relevant material and predict bound excitons in twisted bilayer graphene, which is a two-dimensional gapless structure exhibiting metallic screening. The binding energies calculated by first-principles simulations are surprisingly large. The low-energy effective model reveals that these bound states are produced by a unique destructive coherence between two alike subband resonant excitons. In particular, this destructive coherent effect is not sensitive to the screening and dimensionality, and hence may persist as a general mechanism for creating bound excitons in various metallic structures, opening the door for excitonic applications based on metallic structures.

12 pages and 5 figures

References in corpus (6)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Excitonic Effects on the Optical Response of Graphene and Bilayer Graphene
• Truncation of Periodic Image Interactions for Confined Systems
• Optical properties of graphene nanoribbons: the role of many-body effects
• Tunable Excitons in Biased Bilayer Graphene
• Excitonic Effects in the Optical Spectra of Graphene Nanoribbons

Cited by in corpus (9)

• Electronic properties of graphene-based bilayer systems
• θ-Tunable Photoluminescence from Interlayer Excitons in Twisted Bilayer Graphene
• Strongly bound excitons dominate electronic relaxation in resonantly excited twisted bilayer graphene
• Optical absorption of twisted bilayer graphene with interlayer potential asymmetry
• Anisotropic Electron-Hole Excitation and Large Linear Dichroism in Two-Dimensional Ferromagnet CrSBr with In-Plane Magnetization
• Triangular lattice exciton model
• Probing the bright exciton state in twisted bilayer graphene via resonant Raman scattering
• Excitonic effects in twisted bilayer graphene
• The electronic band structures and optical absorption spectra for incommensurate twisted few-layers graphene