Proximity-Induced Magnetism and Interface Coupling in Topological Heterostructures

Whether used as a platform for novel quantum transport or ultra-efficient spintronics, heterostructures incorporating topologically nontrivial materials are among the most exciting playgrounds in condensed matter physics. In these systems, interfacial symmetry breaking has played a prominent role in achieving the desired functionalities. Heterostructures interfacing superconductors with a quantum anomalous hall insulator (QAHI) have been reported to exhibit signatures of Majorana fermions, while two-dimensional systems with strong spin-orbit interactions have long been suspected of harboring skyrmions at interfaces with perpendicular magnetic materials. Magnetic proximity effects have been prominently used across topologically trivial/nontrivial material interfaces to open gaps in the surface states of topological insulators or to induce topological transitions. A proper understanding of magnetic proximity effects at topologically nontrivial interfaces hinges critically on our ability to precisely isolate the properties of the interface from the bulk of the system. By decomposing the magnetic and electronic properties on a layer-by-layer and element-resolved basis, new quantum material systems may be robustly understood and designed. In this talk, I will discuss our recent progress in applying polarized neutron reflectometry in concert with X-ray scattering, spectroscopy and electron microscopy to uniquely identify modeling solutions in the complex and challenging parameter space of topological insulator [(Bi,Sb)₂Te₃, MnBi₂Te₄], topological crystalline insulator (SnTe), and Dirac semimetal-based heterostructures (Cd₃As₂). We will examine approaches for accurately identifying magnetic proximity effects and other forms of magnetic interface coupling. We will conclude with a discussion on the future of ultra-sensitive probes of magnetic interfaces, with a particular focus on highly multiplexing neutron instrumentation.