Title: Directing Energy Transport at the Nanoscale
Abstract: Spatial direction of energy flow in 2D materials is critical for developing next-generation optoelectronic and thermoelectric applications. However, low-dimensional systems are prone to nanoscale morphological disruptions, such as material edges and localized strain, which can strongly modify charge and heat transport. I investigate this interplay between intrinsic and extrinsic behavior in a model system, anisotropic black phosphorus (BP), with photoemission electron microscopy (PEEM) and ultrafast transmission electron microscopy (UEM) to determine morphological modification of the electronic structure and coherent acoustic phonon propagation with nanoscale resolution. Using PEEM, I show that the optical selection rules of BP are modified at flake edges, resulting in a rotated transition dipole moment. With UEM, I demonstrate that the anisotropy-driven mixing of longitudinal and transverse acoustic phonon modes results in a strongly reduced group velocity of coherent acoustic phonons. These results demonstrate that in-plane broken symmetry can be developed as a novel handle for spatially-selective optical excitation and directional control of heat transport in 2D systems.
Bio: Prakriti P Joshi is a postdoctoral fellow at the Fritz Haber Institute of the Max Planck Society in the group of Professor Sebastian Maehrlein. She was previously a Kadanoff-Rice postdoctoral fellow in the group of Professor Sarah King at the University of Chicago and completed her PhD in Chemical Physics at Columbia University under the supervision of Professor Xiaoyang Zhu. Her research interests lie in controlling phonons, or solid-state vibrations, with spatial resolutions pushing the few-unit cell and atomistic limit to direct heat, charge, and ion transport for energy harvesting and storage applications.
Host: Susanna Widicus Weaver