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Excitonic Instability in Quantum Spin Hall Insulators TlX (X = As, Sb, Bi)
Dongyue Sun1, Yushuo Xu1, Liang-An Qin1
1School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
Researchers identified quantum spin Hall insulators (QSHIs) as promising candidates for excitonic insulators (EIs). This novel EI state, driven by bright excitons, offers an optically accessible signature for detection and a new paradigm of topological EI.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Mechanics
Background:
- Excitonic insulators (EIs) are rare macroscopic quantum phases of matter.
- Realizing EIs has been a significant challenge in condensed matter physics.
- Quantum spin Hall insulators (QSHIs) possess unique electronic properties.
Purpose of the Study:
- To propose and verify QSHIs as viable platforms for achieving excitonic instability.
- To explore the role of quasiparticle (QP) corrections in EI formation.
- To identify novel signatures for detecting EI states.
Main Methods:
- First-principles calculations.
- Many-body perturbation theory.
- Analysis of electronic band structures and exciton properties.
Main Results:
- QSHIs exhibit an atypical inverse QP correction, decoupling band gap and exciton binding energy.
- TlX compounds (X = As, Sb, Bi) were identified as QSHIs with exciton binding energy exceeding the QP band gap.
- A novel EI state composed of bright excitons with negative formation energy and high oscillator strength was discovered.
Conclusions:
- QSHIs provide a promising route to realizing excitonic insulators.
- The identified EI state offers an optically accessible signature for detection.
- The study unveils a new paradigm of bright topological excitonic insulators.
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