University of Minnesota
School of Physics & Astronomy

Condensed Matter Seminar

Thursday, February 11th 2016
11:15 am:
Speaker: Yongtao Cui, Stanford University
Subject: Visualizing Low Dimensional Electronic States in Complex 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 nanoscal. The first study investigates magnetic 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. The second study examines the canonical “edge state” picture of the quantum Hall (QH) effect in graphene. To our surprise, we find an unconventional edge-bulk correlation in graphene devices: the QH transport plateaus occur before the bulk Landau levels are completely filled. This result has implications in both QH transport analysis as well as understanding of general edge transport behaviors in other 2D topological systems.

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