Strong Light-Matter Interactions in 2D Materials
Doctoral thesis, 2026
Integrating 2D materials into high-quality optical microcavities opens the door to fascinating many-particle phenomena, including the formation of exciton-polaritons. These are hybrid quasi-particles inheriting properties of both the constituent photons and excitons. The corresponding change in the dispersion relation has a large impact on the optics, dynamics and transport behaviour of the materials.
In this thesis, we aim to microscopically understand the optical response and propagation of exciton-polaritons in transition metal dichalcogenides (TMDs). The theoretical method is based on the density matrix formalism combined with the Hopfield approach. In particular, we investigate how the exciton diffusion changes in the strong coupling regime, i.e. when exciton-polaritons are formed. Furthermore, we study the impact of dark excitons on the optical response of upper and lower polariton branches in absorption spectra of molybdenum- and tungsten-based TMDs, which are known to be direct and indirect semiconductors, respectively. We show how different experimentally accessible quantities, such as temperature or mirror reflectance, can be exploited to tune the optical response of polaritons. By changing the cavity detuning, we vary the polariton energy relative to the unaffected dark excitons in such a way that we open or close specific phonon-driven scattering channels. In a joint theory-experiment, with the group of Christian Schneider (University of Oldenburg), we show that this controlled switching of scattering channels manifests in characteristic sharp changes in the optical spectra of polaritons. These spectral features can be exploited to extract the position of dark excitons. This suggests new possibilities for exploiting polaritons for fingerprinting nanomaterials via their unique exciton landscape. Overall, this work contributed to a better microscopic understanding of optics, dynamics and transport of exciton-polaritons in technologically promising 2D materials.
In this thesis, we aim to microscopically understand the optical response and propagation of exciton-polaritons in transition metal dichalcogenides (TMDs). The theoretical method is based on the density matrix formalism combined with the Hopfield approach. In particular, we investigate how the exciton diffusion changes in the strong coupling regime, i.e. when exciton-polaritons are formed. Furthermore, we study the impact of dark excitons on the optical response of upper and lower polariton branches in absorption spectra of molybdenum- and tungsten-based TMDs, which are known to be direct and indirect semiconductors, respectively. We show how different experimentally accessible quantities, such as temperature or mirror reflectance, can be exploited to tune the optical response of polaritons. By changing the cavity detuning, we vary the polariton energy relative to the unaffected dark excitons in such a way that we open or close specific phonon-driven scattering channels. In a joint theory-experiment, with the group of Christian Schneider (University of Oldenburg), we show that this controlled switching of scattering channels manifests in characteristic sharp changes in the optical spectra of polaritons. These spectral features can be exploited to extract the position of dark excitons. This suggests new possibilities for exploiting polaritons for fingerprinting nanomaterials via their unique exciton landscape. Overall, this work contributed to a better microscopic understanding of optics, dynamics and transport of exciton-polaritons in technologically promising 2D materials.
absorption
2D materials
exciton-polaritons
detuning
diffusion
Author
Beatriz de Amorim Ferreira
Chalmers, Physics, Condensed Matter and Materials Theory
Revealing Dark Exciton Signatures in Polariton Spectra of 2D Materials
ACS Photonics,;Vol. 11(2024)p. 2215-2220
Journal article
Signatures of dark excitons in exciton–polariton optics of transition metal dichalcogenides
2D Materials,;Vol. 10(2023)
Journal article
Microscopic modeling of exciton-polariton diffusion coefficients in atomically thin semiconductors
Physical Review Materials,;Vol. 6(2022)
Journal article
Light is the fastest particle in the universe, while matter makes up everything
we know. But what happens when we mix both together to interact so strongly?
That is the content of this thesis. We study the interaction of light and
matter, which leads to the formation of new particles called exciton-polaritons.
These particles inherit proprieties of both light and matter. Through theoretical
models, we study how these particles propagate in the medium that supports
them and how their optical properties are shaped by different types of excitons,
including optically ”dark” excitons that are normally invisible to light.
Understanding exciton-polaritons could contribute to photonic and quan-
tum devices, shaping the future of technology where light is used as mean of
transporting information faster than we can today.
we know. But what happens when we mix both together to interact so strongly?
That is the content of this thesis. We study the interaction of light and
matter, which leads to the formation of new particles called exciton-polaritons.
These particles inherit proprieties of both light and matter. Through theoretical
models, we study how these particles propagate in the medium that supports
them and how their optical properties are shaped by different types of excitons,
including optically ”dark” excitons that are normally invisible to light.
Understanding exciton-polaritons could contribute to photonic and quan-
tum devices, shaping the future of technology where light is used as mean of
transporting information faster than we can today.
Subject Categories (SSIF 2025)
Atom and Molecular Physics and Optics
Condensed Matter Physics
Areas of Advance
Nanoscience and Nanotechnology
DOI
10.63959/chalmers.dt/5947
ISBN
978-91-8103-490-5
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5947
Publisher
Chalmers