Spatiotemporal mapping of photocurrent in 2D materials using diamond quantum sensors

Photocurrents are conventionally detected by counting the charge that flows between two contacts, but electrical detection cannot resolve the path that photocurrents travel within a material. Here, we leverage nitrogen-vacancy (NV) center magnetometers to resolve the spatial distribution of photocurrent flow in a 2D material by measuring the magnetic field profile produced by the photocurrents [1]. We reveal that photocurrent in monolayer MoS₂ circulates as a micron-scale vortex under an external magnetic field due to a strong photo-Nernst effect. By synchronizing dynamical decoupling of the sensor spin with pulsed photoexcitation, we significantly enhance sensitivity and resolve current densities as small as 20 nA/μm. Importantly, our pulsed approach allows probing of the temporal dynamics of photocurrent generation with sub-microsecond resolution. This combined spatiotemporal resolution is invaluable for understanding how novel photocurrent generation mechanisms and local variations control the flow of photocurrent in next-generation optoelectronic devices.

[1] B. B. Zhou et al., arXiv:1903.09287 (2019).

In collaboration with P. C. Jerger, K.-H. Lee, M. Fukami, F. Mujid, J. Park, and D. D. Awschalom.