CAREER: Imaging Light-Matter Interactions in Quantum Materials with Nanoscale Quantum Sensors

The conversion of light into electricity, known as photocurrent, is the basis for devices such as photodetectors and solar cells. Applications for these devices include imaging, optical communication, and renewable energy. Enhancing their performance relies on understanding new mechanisms to efficiently generate these photocurrents and how these currents travel within the material.

The team will spatially image the flow of photocurrents inside materials and determine how nanoscale variations affect its generation and transport. These measurements will be made by a noninvasive sensor that uses the quantum properties of an atomic-scale defect in diamond. The sensor will be placed near the material samples to sense weak magnetic fields generated by such photocurrents.

The principal investigator will create hands-on demonstrations and videos to stimulate curiosity in quantum phenomena. These activities will foster intrinsic motivations for students, including from under-represented groups, to pursue education and careers in science and technology. Coursework will emphasize interdisciplinary concepts in quantum information science that encompass materials research, computer science, and engineering.

Electrical measurements based on scanning a focused laser beam, known as scanning photocurrent microscopy, provide powerful real-space views of photocurrent generation; however, the actual path travelled by the photocarriers in the interior of the material is concealed. This missing viewpoint is important to clarify the distinction between bulk and boundary, as well as to understand how local electric, magnetic, and structural variations affect the scattering and relaxation of photocarriers.

To address this challenge, this project develops spatially-resolved magnetometry using the electronic spin of the nitrogen-vacancy center in diamond. Based on confocal microscopy, the technique readily integrates photoexcitation and optical readout of the sensor spin to map stray magnetic fields from photocurrent flow. These magnetic field maps are used to extract the amplitude and direction of photocurrent flow in two-dimensional materials and thin bulk samples.

High sensitivity is achieved by synchronizing pulsed photoexcitation with coherent manipulation of the quantum sensor spin, while high spatial resolution is achieved by scanning a diamond-based atomic force microscope probe. The fundamental understanding of topology, symmetry, and valley polarization pursued here impacts the development of photodetectors, novel information processing devices, and higher efficiency photovoltaics.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.