Condensed Matter/Materials & Biological Physics Seminar with Diana Qiu on Many-Body Effects on Optical Excitations

In low-dimensional and nanostructured materials, the optical response is dominated by correlated electron-hole pairs---or excitons---bound together by the Coulomb interaction. Understanding the energetics and dynamics of these excitons is essential for diverse applications across optoelectronics, quantum information and sensing, as well as energy harvesting and conversion. By now, it is well-established that these large excitonic effects in low dimensional materials are a combined consequence of quantum confinement and inhomogeneous screening. However, many challenges remain in understanding their dynamical processes, especially when it comes to correlating complex experimental signatures with underlying physical phenomena through the use of quantitatively predictive theories. In this talk, I will discuss how excitons in low-dimensional and nanostructured materials, such as monolayer transition metal dichalcogenides and layered perovskites, differ from typical bulk materials. In particular, we will look at how symmetry and dimensionality manifest in the exciton bandstructure and how those features affect exciton diffusion and transport. Another challenge in understanding excitonic behavior is in complex materials, where excitons can correlate independent-particle states across wide energy and length scales. I will discuss new methods we have developed to simulate core-level excitations associated with  x-ray absorption spectra and resonant excitons in topological insulators that can bulk and topological surface states.