Single spin quantum sensing of magnon hydrodynamics in atomically thin CrCl3"

The study of magnon transport is crucial for the development of spintronic devices, where magnon transport in atomically thin “van der Waals” has recently attracted particular interest, owing to new opportunities arising from the versatility and purity of these novel magnetic systems. Interestingly, signatures of a novel magnon transport regime were recently observed [1], where strong magnon-magnon interactions lead to hydrodynamic behavior analogous to sound waves in fluids. This regime features a collective magnon sound mode at low energies that was theoretically predicted [2], but remains experimentally underexplored due to a lack of suitable experimental tools.

Here, we employ single spin magnetometry using scanning nitrogen-vacancy (NV) centers in diamond [3] to address magnon hydrodynamics in bilayers of CrCl3. Using NV decoherence imaging [4], we confirm the previously observed scaling of the NV spin decoherence rate, 1/T2, with the applied magnetic field as a characteristic signature of magnon hydrodynamics. Furthermore, we address a key fingerprint of magnon hydrodynamics in the scaling of 1/T2 with distance from the sample, where our preliminary data tentatively confirm theoretical expectations. Our measurements also reveal nanoscale spatial inhomogeneities in the spin noise amplitude on CrCl3, suggesting an influence of disorder and sample homogeneity on hydrodynamic magnon modes. These observations provide further insight into the nature of hydrodynamic magnon transport, ultimately paving the way for the development of novel magnon-based devices.

[1] R. Xue et al., arXiv:2403.01057

[2] J. F. Rodriguez-Nieva et al., PRB 105, 174412

[3] P. Maletinsky et al., Nature Nano. 7, 320 ; N. Hedrich et al., Phys. Rev. Appl. 14, 064007

[4] J. Rovny et al., Nature Rev. Phys. 2024