Abstract
The detection of photocurrents is central to understanding and harnessing the interaction of light with matter. Although widely used, transport-based detection averages over spatial distributions and can suffer from low photocarrier collection efficiency. Here, we introduce a contact-free method to spatially resolve local photocurrent densities using a proximal quantum magnetometer. We interface monolayer MoS2 with a near-surface ensemble of nitrogen-vacancy centers in diamond and map the generated photothermal current distribution through its magnetic field profile. By synchronizing the photoexcitation with dynamical decoupling of the sensor spin, we extend the sensor's quantum coherence and achieve sensitivities to alternating current densities as small as 20 nA per micron. Our spatiotemporal measurements reveal that the photocurrent circulates as vortices, manifesting the Nernst effect, and rises with a timescale indicative of the system's thermal properties. Our method establishes an unprecedented probe for optoelectronic phenomena, ideally suited to the emerging class of two-dimensional materials, and stimulates applications towards large-area photodetectors and stick-on sources of magnetic fields for quantum control.
Highlights
The extraordinary features of two-dimensional van der Waals systems have opened new directions for tailoring the interaction of light with matter, with the potential to impact technologies for imaging, communications, and energy harvesting
With wide phase-space applicability and potential nanoscale spatial resolution, NV magnetometry has emerged as a premier tool for probing current distributions in materials [13], revealing insights on the structure of vortices in highTc superconductors [20,21] and the effect of microscopic inhomogeneity on transport in graphene [22] and nanowires [23]
Combining spatial and temporal resolution, we characterize the spatial dependence of the temporal response of photothermoelectric effect (PTE) photocurrents in MoS2, showing it to be driven by thermal diffusion
Summary
The extraordinary features of two-dimensional van der Waals systems have opened new directions for tailoring the interaction of light with matter, with the potential to impact technologies for imaging, communications, and energy harvesting. With wide phase-space applicability and potential nanoscale spatial resolution, NV magnetometry has emerged as a premier tool for probing current distributions in materials [13], revealing insights on the structure of vortices in highTc superconductors [20,21] and the effect of microscopic inhomogeneity on transport in graphene [22] and nanowires [23]. These demonstrations all probed direct current (dc) flow and were limited in sensitivity by the inhomogeneous dephasing time TÃ2 of the NV center. Combining spatial and temporal resolution, we characterize the spatial dependence of the temporal response of PTE photocurrents in MoS2, showing it to be driven by thermal diffusion
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