Quantum-impurity relaxometry of magnons in thin films: role of chirality

Quantum impurity (QI) relaxometry - measuring the relaxation rate of an impurity spin due to its coupling with magnetic noise - has recently emerged as a sensitive, local, and non-invasive technique for probing condensed matter systems including magnetic materials. Chirality plays a central role in developing a predictive theoretical model for QI-relaxometry of magnons in thin films where the QI (e.g. Nitrogen-vacancy (NV) center) and magnons act as the sensor and generator of chiral magnetic noise, respectively. Here, we present this theory highlighting the role of chirality and show that our theory 1) is in excellent quantitative agreement with recent NV-relaxometry experiments, and 2) predicts crossover between the two NV ESR relaxation rates as a key signature of the chiral coupling between the NV and magnons which is corroborated by new experiments on Nickel thin films interfaced with NV QI.