Many-Body Effects on Exciton Dynamics and Nonlinear Optics in Low-Dimensional Materials

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 two different frontiers related to the first principles understanding of exciton dynamics. Firstly, we will explore the relationship between exciton dispersion and exciton-phonon interactions and how this can be used to understand transient microscopy experiments and the thermalization dynamics of high energy excitons in the continuum. Secondly, we will look at many-body effects in nonlinear optical response going beyond the perturbative regime. We present first principles calculations of high harmonic generation in 2D materials including many-body effects in the form of electron-hole correlations. We show that many-body effects are especially important to accurately reproduce spectral features in the perpendicular response, which reflect a complex interplay of electron-hole interactions (or exciton effects) in tandem with the many-body renormalization and Berry curvature of the independent quasiparticle bandstructure.