You are here

Professor David Cooke, Department of Physics, McGill University

Event Date: 
Monday, January 14, 2019 - 3:30pm to 4:30pm

Measurement and Control of Electron Dynamics Using THz Pulses

Phase-locked, few-cycle pulses of THz light are powerful tools for both probing and driving ultrafast dynamics of low energy excitations in condensed matter. As an example of THz pulses as a time-resolved probe, I discuss recent multi-THz spectroscopy experiments on the widely researched hybrid organometallic halide perovskites. These solution processable materials have been successfully applied to a variety of optoelectronic devices, most notably high efficiency photovoltaics achieving up to 22% power conversion efficiency in the lab (comparable to silicon). Their long carrier lifetimes and relative insensitivity of their electronic transport properties to the presence of impurities have been puzzling when considering their similarities to other direct band gap semiconductors like GaAs. This led to a proposal that charge carriers exist as large polarons, protected against scattering by their correlation to polar lattice vibrations. In this talk, I show ultrafast THz measurements provide direct evidence for the existence of polarons in these materials, resolving the quantum dynamics of their formation.

In addition, strong field THz pulses can now be used to control the motion of charged particles on sub-cycle time scales. Along these lines, I will discuss our recent work on sub-cycle THz field emission of femtosecond electron wave packets from metal nanotips. We show that through field-assisted tunneling directly from the metal’s Fermi level, impressive electron bunch charges up to 106/shot are emitted on a sub-cycle time scale. These electrons are subsequently accelerated in the local THz field in the vicinity of the nanotip to keV energies over 100 nm length scales. We discuss possible applications as a source for single shot ultrafast electron diffraction and as a test bed for high field physics.

David G. Cooke received his Ph. D. in Physics in 2006 from the University of Alberta under the supervision of Prof. Frank Hegmann, focused on ultrafast THz spectroscopy applied to semiconductors and their nanostructures. He went on to do a postdoc in the group of Prof. Peter Uhd Jepsen at the Technical University of Denmark in 2007. There he was an H. C. Oersteds postdoctoral fellow (2007 – 2009), and later he joined the faculty at DTU as an assistant (2009) and then associate professor (2010). In 2011 he joined the Dept. of Physics at McGill University, Montreal as an assistant professor and is now a tenured associate professor at McGill. His research interests are in the ultrafast conductivity dynamics in novel materials, intense THz field interactions in matter and the development of new technologies for the manipulation of THz light. In 2018, he was awarded a Fessenden professorship to develop particle accelerators based on strong field THz pulses. He has served as sub-committee chair for the OSA conference CLEO and is an associate editor of Optics Express.

Event Location: 
McMaster
Location Details: 
ABB-162