Spatiotemporal Mapping of Photocurrent in a Monolayer Semiconductor Using a Diamond Quantum Sensor

TL;DR

This paper presents a contact-free, high-sensitivity method using diamond quantum sensors to spatially map photocurrents in monolayer semiconductors, revealing vortex patterns and thermal dynamics.

Contribution

It introduces a novel quantum sensing technique to spatially resolve photocurrents in 2D materials without contact, enhancing understanding of optoelectronic phenomena.

Findings

Detected photocurrent vortices indicating Nernst effect

Achieved sensitivity to alternating current densities as low as 20 nA/μm

Mapped thermal and magnetic dynamics of photocurrent evolution

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.