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arXiv · 2006.14705

Bright excitons with negative-mass electrons

Kai-Qiang Lin·Chin Shen Ong·Sebastian Bange·Paulo E. Faria Junior·Bo Peng·Jonas D. Ziegler·Jonas Zipfel·Christian Bäuml·Nicola Paradiso·Kenji Watanabe·Takashi Taniguchi·Christoph Strunk·Bartomeu Monserrat·Jaroslav Fabian·Alexey Chernikov·Diana Y. Qiu·Steven G. Louie·John M. Lupton
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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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Kai-Qiang Lin, Chin Shen Ong, Sebastian Bange, Paulo E. Faria Junior, Bo Peng, Jonas D. Ziegler, Jonas Zipfel, Christian Bäuml, Nicola Paradiso, Kenji Watanabe, Takashi Taniguchi, Christoph Strunk, Bartomeu Monserrat, Jaroslav Fabian, Alexey Chernikov, Diana Y. Qiu, Steven G. Louie, John M. Lupton. 2020-06-25. Bright excitons with negative-mass electrons. https://doi.org/10.1038/s41467-021-25499-2

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