Title: Space – The ‘Final’ Frontier

Exploring electron dynamics in the spatial dimensions

 

Abstract: Since the early days of studying electron dynamics in solid state systems, experimental capabilities have taken great strides – from generating ultrafast pulses across wide swaths of the electromagnetic spectrum (THz to X-Rays), to squeezing electron bunches into sub-picosecond packets, to resolving electron dynamics through photoemitted electrons. With these technologies, achieving high temporal resolution, spectral resolution and momentum resolution has become a relatively straightforward process. These technologies also have the potential for high spatial resolution, birthing techniques such as 4D Electron Microscopy, time-resolved scanning tunnelling microscopy, ultrafast electron microscopy/diffraction and time-resolved photoemission microscopy (TR PEEM). Each with its own advantages, and challenges, the full potential of these capabilities in accessing the spatial dimensions is only just beginning to be explored.

Of these, TR PEEM is uniquely capable of resolving electron dynamics simultaneously in space, time, energy and momentum. By combining the temporal resolution afforded by traditional pump-probe techniques with the spatial resolution afforded by low energy electron microscopy, TR-PEEM allows the visualization of electron transport and dynamics in solid state systems at the nano-, femto-scale. In this talk, I will discuss our recent results in imaging electron dynamics in semiconductor structures. In a type-II heterostructure, we image the highly non-equilibrium distribution of electrons in space and energy at the instant of photoexcitation, and thereafter, make a movie of their redistribution in space as they move towards equilibrium. In a p-doped GaAs semiconductor, we image the electron dynamics within a photoexcitation spot – a region inaccessible with optical experiments, wherein we see unexpected and complex non-equilibrium behaviour. 

Time permitting, I will end with a brief overview of other activities of my group at the newly established Okinawa Institute of Science and Technology (OIST) in Okinawa, Japan.