Observation of ac Photocurrent Vortices in Monolayer MoS₂ Using NV Centers

Photocurrents are central to understanding the interaction of light with matter. Although widely used, transport-based detection cannot resolve the spatial distribution of photocurrents and can suffer from low photocarrier collection efficiency. We demonstrate a contact-free method to spatially and temporally resolve photocurrents using nitrogen-vacancy (NV) centers in diamond, and discover that optical excitation of MoS₂ produces photocurrent vortices [1]. We use a near-surface ensemble of NV centers to map the magnetic field profile of photocurrents in a monolayer of MoS₂ transferred onto the diamond surface. By synchronizing pulsed photoexcitation with NV ac magnetometry, we perform a quantum lock-in measurement to resolve time-dependent photocurrent densities as small as 20 nA/µm. Spatiotemporal measurements reveal a photocurrent rise time, which agrees with modeling of the photothermoelectric effect. This work establishes a novel probe for optoelectronic phenomena, ideal for two-dimensional materials, where making contacts is challenging and can alter the intrinsic material properties.

[1] Zhou, B. B.,* Jerger, P. C.,* Lee, K.-H., Fukami, M., Mujid, F., Park, J., and Awschalom, D. D. Phys. Rev. X 10, 011003, 2020.