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 GW and Bethe-Salpeter equation calculations, confirming strong Coulomb interaction effects in these optical excitations. Our observations provide evidence of excitons in a 2D QSH insulator at room temperature, with excitonic and topological physics deriving from the very same electronic structure.

2024 roadmap on 2D topological insulators

“…1.4 eV at the K/K ′ -points of its hexagonal Brillouin zone, similar to that found in other 2D semiconductors and thus providing a platform for exciton formation. Indeed, the room-temperature optical response measured by laser-modulated photo-reflectivity reveals two prominent resonances that could be unambiguously identified as excitation into bound electron-hole pairs with an excitonic binding energy of about 0.15 eV [79] (see figure 9). This first observation of excitons in a QSHI raises the question to what extent their properties are affected by the topological nature of the underlying band structure, potentially laying the foundation for novel 'topological valleytronics' .…”

Investigating the Corrosion Resistance of Different SiC Crystal Types: From Energy Sectors to Advanced Applications

“…Over the past few decades, with the rapid advancement of semiconductor technology, silicon carbide (SiC) has emerged as one of the most promising semiconductor materials. − As a third-generation semiconductor material, SiC has garnered a significant amount of attention due to its exceptional physical, chemical, and electronic properties. Its notable features include high thermal conductivity, high electron mobility, high critical electric field strength, and excellent stability under high-temperature, high-pressure, and radiation conditions. − These properties make SiC an ideal choice for high-frequency, high-power electronic devices and applications in extreme environments . The chemical stability of SiC, particularly its corrosion resistance in acidic and basic environments, is a key factor in its widespread application in various industrial sectors.…”

Topologically Protected Photovoltaics in Bi Nanoribbons

“…Topological insulators (TIs), on the other hand, have garnered significant attention in recent years due to their potential for use in spintronic devices, among other more fundamental reasons . However, there has been relatively little study of TIs from an optical perspective. − Only recently, for instance, the exciton spectrum in Bi 2 Se 3 was shown to exhibit topological properties …”