Abstract
Photocurrents are central to understanding and harnessing the interaction of light with matter. Here, we introduce a contact-free method to spatially resolve photocurrent distributions using proximal quantum magnetometers. We interface monolayer 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 pulsed photoexcitation with dynamical decoupling of the sensor spin, we extend the sensor’s quantum coherence and resolve time-dependent, two-dimensional current densities as small as , with a projected sensitivity of . Our spatially resolved measurements reveal that optical excitation can generate micron-sized photocurrent vortices in , manifesting a photo-Nernst effect exceeding that of gate-tuned graphene at comparable magnetic fields. We further probe the rise time of the photocurrents and show that thermal diffusion determines its spatial variation. These spatiotemporal capabilities establish an optically accessed, local probe for optoelectronic phenomena, ideally suited to the emerging class of two-dimensional materials, for which making contacts is challenging and can alter the intrinsic material properties.
3 More- Received 26 July 2019
- Revised 14 October 2019
DOI:https://doi.org/10.1103/PhysRevX.10.011003
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Shining light on a material can cause an electric current to flow. This photocurrent is integral to the operation of digital cameras, solar cells, and fiber-optic communication systems. Conventionally, photocurrents are detected by counting the number of charges that flow between two contacts, but electrical detection cannot resolve the path that the photocurrent travels within a material. Here, we demonstrate a novel technique to resolve how photocurrents flow within a material by detecting their local magnetic field. Our demonstration uses highly sensitive, atomic-scale magnetometers to map the distribution of photocurrent flow within a three-atom-thick semiconductor.
Nitrogen-vacancy (NV) centers in diamond are defects whose spins can be used as sensitive magnetometers. Here, we transfer a monolayer semiconductor onto a diamond chip containing a near-surface ensemble of NV centers. We perform a sensing sequence on the NVs and synchronize this sequence with pulsed photoexcitation to detect the local magnetic fields produced by photocurrents in the . We reveal that the photocurrent circulates around the excitation spot because of the Nernst effect, an electrical field that is due to an external magnetic field. We achieve sensitivities to current densities as low as 20 nA/m, comparable to state-of-the-art superconducting quantum interference devices, and investigate the temporal dynamics of photocurrent generation.
Spatially resolved measurements of photocurrent distributions are important for understanding how local variations, such as defects and grain boundaries, affect the flow of current in photosensitive devices. Our technique can characterize the local optoelectronic properties of diverse materials, including monolayer semiconductors and their heterostructures.