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.

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• Twist-angle engineering of excitonic quantum interference and optical nonlinearities in stacked 2D semiconductors
• 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
• Leaky exciton condensates in transition metal dichalcogenide moiré bilayers
• A comprehensive study of complex non-adiabatic exciton dynamics in MoSi${}_2$N${}_4$
• Monolayer C${}_{60}$ networks: A first-principles perspective
• Probing excitons with time-resolved momentum microscopy
• Exchange-Driven Intermixing of Bulk and Topological Surface State by Chiral Excitons in Bi2Se3
• Shaping Exciton Polarization Dynamics in 2D Semiconductors by Tailored Ultrafast Pulses
• Excitons and trions with negative effective masses in two-dimensional semiconductors
• Electronic structure of fullerene nanoribbons
• Robust polaritons in magnetic monolayers of CrI3
• Band-spin-valley coupled exciton physics in antiferromagnetic MnPS${}_3$
• 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
• Excitonic effects in the photocarriers dynamics of two-dimensional materials