The concept of Berry curvature - a geometric property of quantum wavefunctions - has revolutionized our understanding of condensed matter physics. In Weyl semimetals, points of singular Berry curvature (Weyl nodes) act as magnetic monopoles in momentum space, leading to exotic transport phenomena. While the standard Type-I Weyl semimetal predicts a robust, quantized Anomalous Hall Effect (AHE) that is only determined by the separation of Weyl nodes, the reality in complex materials can be far more surprising.
This talk will explore the realization of the "Type-II" Weyl semimetal phase, where the Weyl cone is strongly tilted. I will first introduce the general framework of Berry curvature and how it can be visualized as a magnetic field in momentum space. I will then detail our recent experimental work on the magnetic topological material MnBi2-xSbxTe4. By carefully tuning the doping levels, we can scan the Fermi level across the energy landscape. Instead of the expected plateau, we observe a striking "heartbeat" pattern in the AHE. I will explain how this signature arises from the unique geometry of the Type-II Weyl nodes, where the electron and hole pockets overlap, and the Berry curvature field diverges. This work establishes the "heartbeat" as a distinct fingerprint of Type-II Weyl physics and demonstrates the sensitivity of anomalous transport to the details of band topology.
Prof. Jiun-Haw Chu works in experimental condensed matter physics. His primary research goals are directed towards the discovery and understanding of novel collective behaviors in quantum materials. Prof. Chu obtained his B.S. degree in Electronics Engineering from National Chiao Tung University in 2004, and his Ph.D. degree in Applied Physics from Stanford University in 2012. He did his postdoctoral research at the University of California, Berkeley and Stanford University. In 2016 he joined the faculty of the University of Washington, where he is now a Professor of Physics. Prof. Chu received a Young Investigator Award from the Air Force Office of Scientific Research and a Moore Fellowship in Material Synthesis in 2017, was named a Sloan Research Fellow and a Packard Fellow in Science and Engineering in 2018, and received a Presidential Early Career Award for Scientists and Engineers in 2019. He is also a recipient of the Moore Experimental Physics Investigator Award in 2025.