POLARON DYNAMICS IN LEAD HALIDE PEROVSKITES
We seek to understand the exceptional carrier properties in lead halide perovskites from the viewpoint of polarons, the quasi particles of carriers associated with surrounding lattice distortion. We apply various ultrafast spectroscopic techniques to probe both electron and phonon degrees of freedom in these materials. Our recent discoveries established the role of polaron formation in the unique “crystal-liquid” environment.
Superatom solids are a new class of materials assembled with nanoscale building blocks of superatomic motifs. This synthetic approach allows us to manipulate material structures and their optical, electronic, and magnetic properties. We can tune optical gaps broadly from mid-IR to the visible region, and control the structural dimensions between 0D, 1D, 2D, and 3D. We are studying emergent properties of the materials with optical spectroscopies and scanning-tunneling microscopy.
We use optical pump-probe spectroscopies and time- and angle-resolved photoemission spectroscopy to study carrier dynamics and charge-transfer excitons in two-dimensional van der Waals heterostructures. Of particular interest are momentum conservation in charge transfer and recombination processes and Bose-Einstein condensation of interlayer excitons. We are also interested in the mechanism of defect screening in two-dimensional materials.
Singlet fission is the photo-chemical process where one singlet exciton splits into two triplet excitons. The exciton multiplication process can potentially boost the performance of a single-junction solar cell, a photo detector, and perhaps a multi-electron photocatalyst, but the microscopic understanding of singlet fission is necessary. We use multiple ultrafast spectroscopic techniques to understand the singlet fission rates and to explore the harvesting of triplets from the singlet fission process.
LIGHT-MATTER INTERACTIONS IN WAVEGUIDING SYSTEMS
We study the fundamental interaction of light with matter, and the resulting polariton condensates in low-dimensional wave-guiding systems. In particular, we aim to understand the fundamental scattering processes responsible for polariton condensation and coherent light emission from these one-dimensional systems.
The van der Waals interfaces of molecular donor/acceptor are central to concepts and emerging technologies of light-electricity interconversion. Examples include, among others, solar cells, photodetectors, and light emitting diodes. A salient feature in van der Waals interfaces is the poorly screened Coulomb potential that can give rise to bound electron–hole pairs across the interface, i.e., charge transfer (CT) excitons. We are studying these processes with a range of optical and photoelectron probes.