Multimodal scanning-probe quantum sensing of quantum materials

Spin-defect-based quantum microscopy has recently made transformative advances in cutting-edge scientific research and technological innovation. The high sensitivity, high spatial resolution and excellent measurement modalities of quantum spin defects open up a range of opportunities at the forefront of condensed-matter physics research. Many of the advantages of this approach result from the quantum mechanical nature of the sensors, which offer functionalities that are not available with their classical counterparts. In this Review, we provide an overview of progress on scanning-probe nitrogen-vacancy quantum sensing research and its application to investigating the physics of emergent quantum materials with nanoscale spatial resolution. We also discuss quantum sensing platforms built on more recently discovered spin defects in one-dimensional and two-dimensional materials beyond nitrogen-vacancy centres. We conclude with an outlook on future directions and opportunities for these rapidly advancing quantum sensing technologies.