Using Ultrashort Light Pulses to Probe and Control Quasiparticle Dynamics in Topological Materials*

Low energy excitations can shed light on the interplay between different degrees of freedom in complex materials. Ultrashort optical and terahertz (THz) pulses can be used to both drive and probe these excitations. This is particularly useful in topological materials, since coupling these excitations to light can potentially enable control of their properties. Here, the use of ultrafast THz spectroscopy to separately probe the dynamics of surface and bulk carriers and drive nonlinear phonon dynamics in the topological insulator Bi₂Se₃ will be discussed. We will also describe recent experiments using nonlinear optical techniques to examine quasiparticle dynamics in the Weyl semimetals WTe₂ and TaAs.