Dr. Keji Lai, University of Texas atAustin
Microwave Microscopy of Topological Acoustics
Abstract: Topological phononics offers numerous opportunities in manipulating elastic waves that can propagate in solids without being back-scattered. Due to the lack of nanoscale imaging tools that aid the system design, however, spatially resolved acoustic metamaterial studies have been mostly demonstrated in systems operating at kilohertz to megahertz frequencies. In this talk, I will discuss the visualization of gigahertz valley Hall and spin Hall effects in nanoelectromechanical membranes. Propagation of elastic wave through phononic crystals is directly observed by microwave microscopy with unprecedented sensitivity (sub-100fm) and spatial resolution (sub-100nm). The topologically protected edge states are vividly seen in both real space and momentum space. The robust transport is evident from the wave transmission across local disorder and around sharp corners, as well as the power distribution into multiple edge channels. Our work paves the way to exploit topological physics in integrated acousto-electronic systems for classical and quantum information processing in the microwave regime.
Bio:
Professional Preparation:
- Tsinghua University Electrical Engineering B.S. 2001
- Princeton University Electrical Engineering Ph.D. 2006
- Stanford University Applied Physics Postdoc 2006 – 2011
- Stanford University Applied Physics Research scientist 2011 – 2012
Appointments:
- Professor: Physics, University of Texas at Austin 2024 – Present
- Associate Professor: Physics, University of Texas at Austin 2018 – 2024
- Assistant Professor: Physics, University of Texas at Austin 2012 – 2018
Awards:
- Gordon and Betty Moore Foundation Experimental Physics Investigator 2023 – 2028
- Trull Centennial Professorship in Physics, University of Texas at Austin 2022 – 2025
- Presidential Early Career Awards for Scientists and Engineers (PECASE) 2016
- International Union of Pure and Applied Physics (IUPAP) C10 Young Scientist Prize in the Structure and Dynamics of Condensed Matter 2015
- Department of Energy EARLY CAREER Award 2013
- King Abdullah University of Science and Technology (KAUST) Global Research Partnership Postdoctoral Research Fellowship at Stanford University 2008 – 2011
- Karel Urbanek Postdoctoral Fellowship, Stanford University 2006 – 2008
Selected Publications (~ 100 publications, ~ 11,000 citations, h-index: 49):
- D. Lee, Y. Jiang, X. Zhang, S. Jahanbani, C. Wen, Q. Zhang, AT C. Johnson, K. Lai, “Klein tunneling of gigahertz elastic waves in nanoelectromechanical metamaterials”, Device 2, 100474 (2024).
- Q. Zhang, D. Lee, L. Zheng, X. Ma, S. I. Meyer, L. He, H. Ye, Z. Gong, B. Zhen, K. Lai, A.T. Johnson, “Gigahertz topological valley Hall effect in nanoelectromechanical phononic crystals”, Nature Electron. 5, 157 (2022).
- X. Ma, F. Zhang, Z. Chu, J. Hao, X. Chen, J. Quan, Z. Huang, X. Wang, X. Li, Y. Yan, K. Zhu, and K. Lai, “Superior photo-carrier diffusion dynamics in organic-inorganic hybrid perovskites revealed by spatiotemporal conductivity imaging”, Nature Commun. 12, 5009 (2021).
- Z. Chu, L. Zheng, and K. Lai, “Microwave Microscopy and Its Applications”, Annual Review of Materials Research 50, 105 (2020).
- Z. Chu, C.-Y. Wang, J. Quan, C. Zhang, C. Lei, A. Han, X. Ma, H.-L. Tang, D. Abeysinghe, M. Staab, X. Zhang, A. H MacDonald, V.Tung, X. Li, C.-K. Shih, and K. Lai, “Unveiling defect-mediated carrier dynamics in monolayer semiconductors by spatiotemporal microwave imaging”, Proc. Natl. Acad. Sci. 117, 13908 (2020).
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