Excitonic Physics of Transition Metal Dichalcogenide Monolayers and Heterostructures

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The optical physics and applications of the transition metal dichalcogenide monolayer are dominated by excitonic and trionic states due to the confinement-enhanced coulomb interactions between electrons and holes. The strongly bound nature of these states means that large wavevector dark excitonic states are stable even at room temperature. Whilst the indirect effect of these states on luminescence and excitonic linewidths is well established the only direct probe of them currently is double resonance Raman scattering. Moire effects observed in homo and heterobilayers of these materials are another hot topic. Here Raman scattering can be used to directly probe the moire vectors and by tuning the excitation source to different electronic resonances it is possible to probe how the different excitonic states interact with the moire structure. In heterobilayers the ability to associate particular Raman peaks with phonons unique to each layer means that Raman scattering can be used to probe the hybridisation of excitons between the two layers. My project will involve the use of resonance Raman scattering and other high resolution laser spectroscopies to study the excitonic, particularly dark excitonic, physics in these extremely important materials. During the project I will study isotopically pure binary materials, quaternary alloys and the effect of strain on the bright and dark excitonic states accessible via resonance Raman scattering.