Quasiparticle recombination in the unconventional superconductor T$_d$-MoTe$_2$

Quasiparticle relaxation and recombination in superconductors can not only elucidate the pairing mechanisms but also set performance limits on superconducting devices, such as kinetic inductance detectors and parametric amplifiers. However, limited probes exist to study quasiparticle dynamics in microscopic samples of atomically thin van der Waals (vdW) materials, which often exhibit superconductivity coexisting with other exotic phases of matter. To this end, we present a novel pump-probe technique to measure the quasiparticle recombination rate in T$_d$-MoTe$_2$, a vdW Weyl semimetal that hosts topological states and unconventional superconductivity. We demonstrate how we use superconducting microwave resonators to break Cooper pairs in micron-scale samples and excite quasiparticles right above the superconducting gap edge. We use this technique to probe quasiparticle dynamics and show time-domain measurements of quasiparticle recombination in T$_d$-MoTe$_2$ as a function of temperature and microwave power. Our results show promise for this technique as a powerful tool to understand the nature of pairing in unconventional superconductors.