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Phys Rev Lett. 2014 Aug 15;113(7):076802. Epub 2014 Aug 13.

Exciton binding energy and nonhydrogenic Rydberg series in monolayer WS(2).

Author information

1
Departments of Physics and Electrical Engineering, Columbia University, 538 West 120th Street, New York, New York 10027, USA.
2
Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
3
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.

Abstract

We have experimentally determined the energies of the ground and first four excited excitonic states of the fundamental optical transition in monolayer WS_{2}, a model system for the growing class of atomically thin two-dimensional semiconductor crystals. From the spectra, we establish a large exciton binding energy of 0.32 eV and a pronounced deviation from the usual hydrogenic Rydberg series of energy levels of the excitonic states. We explain both of these results using a microscopic theory in which the nonlocal nature of the effective dielectric screening modifies the functional form of the Coulomb interaction. These strong but unconventional electron-hole interactions are expected to be ubiquitous in atomically thin materials.

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