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"For insightful experiments on the electrodynamic response of topological insulators and the discovery of the topological magneto-electric effect."Background:
Liang Wu, Ph.D., received his undergraduate degree in physics from Nanjing University (China) in 2010 and his Ph.D. in physics in 2015 from Johns Hopkins University (Baltimore, Md.). For his thesis research, he worked with Peter Armitage, Ph.D., to study low-energy electrodynamics of the surface states of three-dimensional topological insulators using time-domain terahertz spectroscopy. He observed the topological phase transition in (Bi1-xInx)2Se3 as well as cyclotron resonances and electron-phonon coupling in the bulk-insulating topological insulator Cu0.02Bi2Se3. Dr. Wu also observed quantized Faraday and Kerr rotation in the units of the fine structure constant in the topological insulator Bi2Se3. This result is consistent with half-integer quantized Hall conductance on each surface, and therefore provides evidence for long-sought axion electrodynamics and the topological magneto-electric effect. This experiment provides a measure of the fine structure constant based on a topological invariant in a solid-state context. This work on quantized rotation also showed how can optics observe quantized Hall conductance without involving the edge states. Since December 2015, Dr. Wu has been working with Joe Orenstein, Ph.D., as a postdoctoral researcher at the University of California, Berkeley. He continues to develop and use novel optical and terahertz tools to reveal new phenomena in quantum materials, including Weyl semimetals, pnictide superconductors, quantum antiferromagnets, and spin liquids. Most recently, Dr Wu discovered a giant anisotropic nonlinear optical response in transition metal monopnictide Weyl semimetals.