Light-Matter Interactions in Transition-Metal Dichalcogenides
Gogna, Rahul
2021
Abstract
Transition Metal Dichalcogenides (TMDCs) have recently become a very popular topic of research due to their wide range of novel optical properties. Many of these materials feature excitons with large oscillator strengths and binding energies, making them an attractive choice as a material for exploring exciton-polariton physics. TMDCs are also very versatile, and can be combined with each other to form arbitrary combinations of materials that can have interesting, tunable properties that change depending on how the heterostructures are constructed. In this thesis, we will look at several different projects concerning light-matter coupling in TMDCs. First, we numerically calculate the properties of photonic crystals designed to exhibit guided-mode resonances for the purposes of achieving strong coupling with evanescently coupled group VI TMDC monolayers. We detail the optimization of these devices, and show that particular attention needs to be paid to the thickness of the device to ensure maximum exciton-photon coupling. We also demonstrate that the in-plane patterning makes these devices suitable for on-chip integration, and that they have more interesting dispersion properties compared to standard optical cavities. These numerical results of strong coupling are corroborated by experimental results which show that this type of platform can indeed support polaritons at both cryogenic and room temperatures, making this the first demonstration of all-dielectric photonic crystal polaritons created with TMDCs. This is followed by numerical results detailing a dual-band photonic cavity designed to have independently tunable resonances, for coupling to multiple different emitters in a single layer of active material, in contrast to standard types of cavities whose modes are not independently tunable. The cavity combines a traditional Fabry-Perot type cavity with a guided-mode resonance type cavity, and the two modes both have electric field distributions that strongly couple to the active material at the center of the cavity, a result which is generally not possible with standard optical cavities. Then, we present experimental results showing highly valley-polarized emission from hBN encapsulated MoSe2/WSe2 heterobilayers. The emission has two prominent peaks, one of which has the standard optical selection rule and one of which has a flipped optical selection rule, and both exhibit high valley polarization. These results are presented alongside some numerical calculations about the electronic and optical properties of TMDC heterobilayers. Finally, we present experimental results, supported by numerical calculations, which demonstrate for the first time that the group VII material ReS2 is capable of supporting self-hybridized polaritons, which manifest as a splitting of the exciton absorption. The high background index of the material results in an effective optical cavity that is formed by the ReS2/Air and ReS2/substrate (Au or Sapphire) interfaces. We fully characterize the polarization resolved absorption, and present transfer matrix calculations which are in excellent agreement with the experimental results, making this the first demonstration of self-hybridized polaritons in group VII materials.Deep Blue DOI
Subjects
Transition Metal Dichalcogenides Polaritons
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