Observation of room temperature excitons in an atomically thin topological insulator

Abstract

Optical spectroscopy of ultimately thin materials has significantly enhanced our understanding of collective excitations in low-dimensional semiconductors. This is particularly reflected by the rich physics of excitons in atomically thin crystals which uniquely arises from the interplay of strong Coulomb correlation, spin-orbit coupling (SOC), and lattice geometry. Here we extend the field by reporting the observation of room temperature excitons in a material of non-trivial global topology. We study the fundamental optical excitation spectrum of a single layer of bismuth atoms epitaxially grown on a SiC substrate (hereafter bismuthene or Bi/SiC) which has been established as a large-gap, two-dimensional (2D) quantum spin Hall (QSH) insulator. Strongly developed optical resonances are observed to emerge around the direct gap at the K and K' points of the Brillouin zone, indicating the formation of bound excitons with considerable oscillator strength. These experimental findings are corroborated, concerning both the character of the excitonic resonances as well as their energy scale, by ab-initio \emph{GW} and Bethe-Salpeter equation calculations, confirming strong Coulomb interaction effects in these optical excitations. Our observations provide the first evidence of excitons in a 2D QSH insulator at room temperature, with excitonic and topological physics deriving from the very same electronic structure.

References in corpus (11)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Valley polarization in MoS2 monolayers by optical pumping
• Observation of giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
• Observation of the Quantum Spin Hall Effect up to 100 Kelvin in a Monolayer Crystal
• Many-body perturbation theory calculations using the yambo code
• Exciton condensation and charge fractionalization in a topological insulator film
• {\it Ab--initio} finite temperature excitons
• Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB6
• Excitons and Optical Absorption on the Surface of a Strong Topological Insulator with a Magnetic Energy Gap
• Exciton topology and condensation in a model quantum spin Hall insulator
• Chiral Topological Excitons in a Chern Band Insulator

Cited by in corpus (9)

• Roadmap for Photonics with 2D Materials
• 2024 roadmap on 2D topological insulators
• Optically controlled single-valley exciton doublet states with tunable internal spin structures and spin magnetization generation
• Emergent bright excitons with Rashba spin-orbit coupling in atomic monolayers
• Dual topological insulator with mirror symmetry protected helical edge states
• Tunable resonant s-p mixing of excitons in van der Waals heterostructures
• Interface engineering of van der Waals heterostructures towards energy-efficient quantum devices operating at high temperatures
• Topologically tunable polaritons based on two-dimensional crystals in a photonic lattice
• Variational and field-theoretical approach to exciton-exciton interactions and biexcitons in semiconductors