Optical Selection Rule of Excitons in Gapped Chiral Fermion Systems

Abstract

We show that the exciton optical selection rule in gapped chiral fermion systems is governed by their winding number $w$, a topological quantity of the Bloch bands. Specifically, in a $C_N$-invariant chiral fermion system, the angular momentum of bright exciton states is given by $w\pm 1+nN$ with $n$ being an integer. We demonstrate our theory by proposing two chiral fermion systems capable of hosting dark $s$-like excitons: gapped surface states of a topological crystalline insulator with $C_4$ rotational symmetry and biased $3R$-stacked MoS${}_2$ bilayers. In the latter case, we show that gating can be used to tune the $s$-like excitons from bright to dark by changing the winding number. Our theory thus provides a pathway to electrical control of optical transitions in two-dimensional material.

8 pages, 4 figures

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• Nonlinear optical selection rules of excitons in monolayer transition metal dichalcogenides
• Half Excitonic Insulator: A Single-Spin Bose-Einstein Condensate
• Optically Probing Tunable Band Topology in Atomic Monolayers
• Strain-induced bound states in transition-metal dichalcogenide bubbles
• Two-photon absorption in two-dimensional materials: The case of hexagonal boron nitride
• Flipping exciton angular momentum with chiral phonons in MoSe${}_2$/WSe${}_2$ heterobilayers
• Absorption and optical selection rules of tunable excitons in biased bilayer graphene
• Topological flat bands without magic angles in massive twisted bilayer graphenes
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• Two limit cases of twisted hBN bilayers and their excitonic response
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• Optically controlled single-valley exciton doublet states with tunable internal spin structures and spin magnetization generation
• Exchange-Driven Intermixing of Bulk and Topological Surface State by Chiral Excitons in Bi2Se3
• Anisotropic linear and non-linear excitonic optical properties of buckled monolayer semiconductors
• Inheritance of the exciton geometric structure from Bloch electrons in two-dimensional layered semiconductors
• Geometric band properties in strained monolayer transition metal dichalcogenides using simple band structures
• Symmetry Classification for Alternating Excitons in Two-Dimensional Altermagnets
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• Brightening odd-parity excitons in transition-metal dichalcogenides: Rashba spin-orbit interaction, skyrmions, and cavity polaritons
• Tunable resonant s-p mixing of excitons in van der Waals heterostructures
• A Quantized Interband Topological Index in Two-Dimensional Systems
• Gauge-invariant optical selection rules for excitons
• Optical selection rules of topological excitons in flat bands