Emergent Interface Electronic States in Quantum Materials

Low dimensional systems, such as atomically thin materials and material interfaces, offer a rich ground to discover new types of electronic states. Spatially resolved electrical probes provide direct access to these states on the mesoscopic scale, complementing conventional transport techniques. In this talk, I will present two comprehensive studies on 2D electronic states employing Microwave Impedance Microscopy (MIM), a scanning probe technique that senses materials’ capacitance and conductivity on the nanoscale. The first study investigates domain walls in a unique all-in-all-out magnetic insulator, Nd2Ir2O7. Through a combined study of MIM, transport, and X-ray micro-diffraction, we conclusively show that metallic states emerge at the magnetic domain walls when the all-in-all-out magnetic order forms with a concomitant metal-insulator transition occurring in the bulk. This represents a new type of interface electronic states in a both chemically and structurally homogeneous material. In the second part, we use MIM to examine the edge conduction in several 2D topological systems, including the quantum Hall (QH) effect in graphene, the quantum spin Hall (QSH) effect in HgTe quantum wells and monolayer WTe2, and the quantum anomalous Hall (QAH) effect in magnetic TI films. Correlating spatial conductivity profiles with transport measurement provides valuable insights into the underlying physics involved, which is essential to establish the mesoscopic picture for the edge conduction in such systems.