Exciton Transport & Diffusion
Understanding the dynamics and dissociation of photoexcited states is crucial for energy harvesting and conversion and applications of optoelectronic devices. Recent advances in spatially-resolved transient absorption microscopy have allowed researchers to observe exciton diffusion in real-time. The theoretical picture, however, is complicated by the fact that many different processes, such as recombination and exciton-phonon and exciton-exciton scattering, contribute to exciton diffusion. Our group is interested in developing ab initio approaches to study exciton diffusion, transport and dissociation.
- Nonanalyticity, Valley Quantum Phases, and Lightlike Exciton Dispersion in Monolayer Transition Metal Dichalcogenides: Theory and First-Principles Calculations
- Signatures of Dimensionality and Symmetry in Exciton Band Structure: Consequences for Exciton Dynamics and Transport
Many important photo-processes and experiments of interest involve ultrafast and high-intensity pulses of light that fall well outside the regime of linear response. Such experiments are often difficult to interpret in the absence of reliable, ab initio theory. Our group develops ab initio time-dependent methods based on non-equilibrium Green’s function approaches to study excited state dynamics, explore nonlinear optical processes and search for novel, field-driven phases.
Heterojunctions, Interfaces and Substrates
The research excitement surrounding layered van der Waals materials lies in part in the ability to peel-off, stack, and manipulate single layers, leading to an endless variety of possible structures and the possibility of tuning materials properties and phases through different stacking, twisting and proximity effects.
- Screening and Many-Body Effects in Two-Dimensional Crystal: Monolayer MoS2
- Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
- Environmental Screening Effects in 2D Materials: Renormalization of the Bandgap, Electronic Structure, and Optical Spectra of Few-Layer Black Phosphorus
Another pathway for engineering optical excitations is through the introduction and control of structural/chemical defects. We found that the electron-hole interaction can result in hybridization of the defect and bulk states, and tuning the defect energy levels can be used to control the degree of hybridization. These defects have potential applications for quantum information, sensing and single-photon emission.
- The role of chalcogen vacancies for atomic defect emission in MoS2
- Rational Passivation of Sulfur Vacancy Defects in Two-Dimensional Transition Metal Dichalcogenides