Terahertz nonlinear and parametric dynamics in quantum materials

Coherent terahertz pulses are a powerful probe of low-energy electrodynamics in quantum materials. This includes materials such as superconductors and charge density wave materials since ~0.1-10 THz is the appropriate energy scale to access electrodynamic signatures associated with condensate responses. In this contribution, we focus on coherent coherent terahertz dynamics in the putative excitonic insulator tantalum nickel selenide (TNS). We observe a broad reflectivity enhancement (~0.5 - 7 THz) that serves as a reporter of a condensate-like behavior in TNS which is difficult to otherwise detect. More broadly, our results highlight that nonlinear terahertz techniques enable characterization of subtle interactions in quantum materials. In particular, quantum materials can exhibit strong nonlinear and parametric light-matter interactions that encode information the many-body interactions.