Magnetic Imaging of Emergent Phenomena in Topological Quantum Materials

Using topology to classify electronic states of quantum matters, physicists have developed new concepts of topological orders and topological phases such as topological insulators and semimetals. In topological magnets, the topological properties are tied to the order parameters. Boundaries such as domain walls, surfaces or edges host topological boundary states that dictate their electronic properties and functionalities. Therefore, it is imperative to visualize the magnetic configuration of these mesoscopic objects in order to understand the fundamental mechanisms of emergent functionalities. The long-term vision of this project is to explore the control and manipulation of these topological boundary states for novel applications in low-power and quantum electronics. To achieve these goals, the PI and his students have set up a one-of-a-kind cryogenic magnetic force microscope (MFM) with superior sensitivity (single atomic layer) and high spatial resolution. The cryogenic MFM can perform magnetic imaging in a wide temperature range with high magnetic field and high voltage while measuring in-situ transport. With the prior DOE support, the PI and his students have explored and discovered many interesting phenomena in several topological magnets, such as visualizing curvilinear domain walls in antiferromagnets, surface metamagnetic transitions and skyrmion lattice at room temperature. Building upon these prior successes, the PI and his students will explore a plethora of exciting topological or emergent quantum phenomena that can be tuned or modulated by external magnetic and/or electric fields in several topological magnets. Combining magnetic imaging and complementary techniques, the PI and his students will investigate topological spin texture, surface magnetism and transitions in antiferromagnets, the topological correlated physics in kagome magnets, and the quantum transport of chiral edge states in magnetic topological insulators. In addition, the PI and his students will build a next-generation MFM for magnetic imaging in millikelvin temperature and very high magnetic field, which will enable exploration of the topological and quantum phenomena at the quantum limit. The outcome of the proposed research will not only advance the fundamental understanding of intriguing topological phenomena such as two-dimensional magnetism on surface or domain walls, chiral edge states and chiral spin texture, but will also have impact on spintronics, quantum interconnect, and energy-efficient applications.