Bright excitons with negative-mass electrons

Abstract

Bound electron-hole excitonic states are generally not expected to form with charges of negative effective mass. We identify such excitons in a single layer of the semiconductor WSe2, where they give rise to narrow-band upconverted photoluminescence in the UV, at an energy of 1.66 eV above the first band-edge excitonic transition. Negative band curvature and strong electron-phonon coupling result in a cascaded phonon progression with equidistant peaks in the photoluminescence spectrum, resolvable to ninth order. Ab initio GW-BSE calculations with full electron-hole correlations unmask and explain the admixture of upper conduction-band states to this complex many-body excitation: an optically bright, bound exciton in resonance with the semiconductor continuum. This exciton is responsible for atomic-like quantum-interference phenomena such as electromagnetically induced transparency. Since band curvature can be tuned by pressure or strain, synthesis of exotic quasiparticles such as flat-band excitons with infinite reduced mass becomes feasible.

References in corpus (9)

• Tightly bound excitons in monolayer WSe2
• k.p theory for two-dimensional transition metal dichalcogenide semiconductors
• Probing Excitonic Dark States in Single-layer Tungsten Disulfide
• Electrical Control of Second-Harmonic Generation in a WSe2 Monolayer Transistor
• Intrinsic Transport Properties of Electrons and Holes in Monolayer Transition Metal Dichalcogenides
• Nonlinear Photoluminescence in Atomically Thin Layered WSe2 Arising from Diffusion-Assisted Exciton-Exciton Annihilation
• Twist-angle engineering of excitonic quantum interference and optical nonlinearities in stacked 2D semiconductors
• Efficient phonon cascades in hot photoluminescence of WSe${}_2$ monolayers
• Auger recombination of dark excitons in $\mathrm{W}{\mathrm{S}}_2$ and $\mathrm{WS}{\mathrm{e}}_2$ monolayers

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• Unconventional Excitonic States with Phonon Sidebands in Layered Silicon Diphosphide
• Large exciton binding energies in MnPS${}_3$ as a case study of vdW layered magnet
• Dark exciton-exciton annihilation in monolayer WSe${}_2$
• Optical signature of cascade transitions between moiré interlayer excitons
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• Pump-driven opto-magnetic properties in semiconducting transition-metal dichalcogenides: an analytical model
• Strain-Enabled Giant Second-Order Susceptibility in Monolayer WSe${}_2$
• Microscopic Theory of Exciton-Exciton Annihilation in Two-Dimensional Semiconductors
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