Special Seminar
Name: Mr. Arjun Ashoka
Affiliation: Harvard University
Title: “Tabletop Ultrafast Optical Probes of Semiconductors Across Time and Length Scales”
Date & Time: Monday, 10th November 2025 at 11:00 a.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Buidling
Abstract:
Conventional semiconductors have historically been idealized as perfectly periodic structures where Bloch’s theorem has been applied with great success. However, in reality, condensed matter systems often deviate from this periodic framework across several time and length scales, ranging from static, long-range polycrystalline disorder to dynamic, short-range lattice vibrations. The ramifications of this deviation often manifest themselves on the native timescales of electronic and lattice vibrations, i.e., atto to picoseconds. I will discuss how we can extract exact dielectric constants on these timescales, retrieving femtosecond microscopic information in three-dimensions, and demonstrating the unexpected phenomenon of spin-domain formation due to long-range static symmetry disorder. I will also demonstrate how we can push these techniques into the attosecond regime with tabletop optical experiments, visualising the formation of images in the ubiquitous widefield optical microscope. Finally, I will lay out a new experimental scheme to study ultrafast equilibrium thermodynamics in material systems.