Excitons in van der Waals heterostructures: The important role of dielectric screening

By S. Latini, T. Olsen, Kristian Sommer Thygesen. 2015

223 citations recorded by the source corpus.

The existence of strongly bound excitons is one of the hallmarks of the newly discovered atomically thin semi-conductors. While it is understood that the large binding energy is mainly due to the weak dielectric screening in two dimensions (2D), a systematic investigation of the role of screening on 2D excitons is still lacking. Here we provide a critical assessment of a widely used 2D hydrogenic exciton model which assumes a dielectric function of the form {\epsilon}(q) = 1 + 2{\pi}{\alpha}q, and we develop a quasi-2D model with a much broader applicability. Within the quasi-2D picture, electrons and holes are described as in-plane point charges with a finite extension in the perpendicular direction and their interaction is screened by a dielectric function with a non-linear q-dependence which is computed ab-initio. The screened interaction is used in a generalized Mott-Wannier model to calculate exciton binding energies in both isolated and supported 2D materials. For isolated 2D materials, the quasi-2D treatment yields results almost identical to those of the strict 2D model and both are in good agreement with ab-initio many-body calculations. On the other hand, for more complex structures such as supported layers or layers embedded in a van der Waals heterostructure, the size of the exciton in reciprocal space extends well beyond the linear regime of the dielectric function and a quasi-2D description has to replace the 2D one. Our methodology has the merit of providing a seamless connection between the strict 2D limit of isolated monolayer materials and the more bulk-like screening characteristics of supported 2D materials or van der Waals heterostructures.

Subfields: Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/588b2b2d181c6219c0c1d3bd4cc314c6e21510bb

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In Materials Chemistry

Citations in the corpus

The Computational 2D Materials Database: high-throughput modeling and discovery of atomically thin crystals (2018, background): “In general, calculations of electronic excitations of 2D materials converge rather slowly with respect to k-points due to the non-analytic behavior of the dielectric function in the vicinity of q = 0 [119, 137, 138].”