Terahertz frequency switching in topological Weyl semimetals

I will describe femtosecond-resolution crystallographic measurements probing dynamic switching responses driven by terahertz light pulses in topological Weyl semimetals, focusing on the 2D transition metal dichalcogenide WTe₂. We describe a new mechanism for driving large amplitude interlayer shear oscillations with ~1% strain amplitudes, leading to a topologically distinct metastable phase. We further show that such shear strain serves as an ultrafast, energy-efficient means to induce more robust, well-separated Weyl points or to annihilate all Weyl points of opposite chirality. I will also discuss new efforts investigating other means for manipulating the topological phase diagram and interlayer stacking of this material through the application of pure electric fields and through doping/intercalation as probed by both optical and transport measurements. This work defines new possibilities for ultrafast manipulation of the topological properties of solids and for the development of new types of topological optoelectronic devices.