Watching Atoms Move with Terahertz Scanning Probe Microscopy

Prof. Tyler L. Cocker from "Department of Physics and Astronomy Michigan State University, USA"

@ Room 212, CCMS/PHYSICS Building

Abstract:

The terahertz range of the electromagnetic spectrum hosts material excitations that are particularly important for nanotechnology, such as the collective motion of charges, spins, and ions. These excitations are often studied with terahertz time-domain spectroscopy, which directly measures the oscillating electric field of a terahertz light pulse and relates it to key material processes through the light-matter interaction. Coherent detection of terahertz fields can even reveal dynamics faster than a terahertz cycle[1,2]. However, conventional terahertz time-domain spectroscopy measurements average the sample response over macroscopic length scales due to the diffraction limit. Experimental techniques have been developed based on scanning probes to improve the spatial resolution of terahertz science[3], as visualized in Figure 1. On the far left of Figure 1, lightwave-driven scanning tunneling microscopy[4-7] reaches the atomic limit by coherently controlling quantum tunneling of electrons between a tip and sample with the oscillating terahertz field. At present, it is the only experimental technique capable of simultaneous atomic spatial resolution and ultrafast temporal resolution. In this talk, I will first introduce the central concepts of lightwave-driven microscopy and then show how it can be used to perform atomic-scale terahertz time-domain spectroscopy[8], visualize electron densities in single molecules[5,7], and even control topological phase transitions in materials.

 

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