IMSE Seminar with Hanyu Zhu on Chiral Phonon-Spin Dynamics in Hexagonal Lattices
The static structure-property relationship is central to materials science. What happens to the properties when the structure keeps evolving? In many cases, the mechanical and electronic properties are determined by the instantaneous lattice structure, but this may not always be true. In particular, a qualitative distinction can be made by atomic motions called “chiral phonons,” which breaks time-reversal symmetry on average, and would in principle affect all properties protected by such symmetry. The presence of chiral phonons is simply guaranteed by multi-fold rotational symmetry, and thus is rather common in materials. In this talk, I will first introduce the concept of chiral phonons in two-dimensional (2D) materials, which have promising applications in nanoscale electronics, optoelectronics and spintronics because they can be free from defects in the atomically thin limit. The chiral phonons are optically controllable and exhibit chiral interaction with charged carriers with spin-valley locking in transition metal dichalcogenide semiconductors. I will then introduce our discovery of coherent coupling, or quantum cooperativity, between phonons and magnons in 2D antiferromagnets that leads to nontrivial topology. Finally, I will discuss more generally the coupling between chiral phonons and spins with recent experimental findings. Together, these phenomena demonstrate a new paradigm of dynamic structural-property relationship in quantum materials.
Dr. Zhu is an assistant professor of Materials Science and NanoEngineering. He earned his B.S. in Mathematics and Physics at Tsinghua University in China, where he got into the field of nanomaterials. He obtained his Ph.D. in Applied Science and Technology at the University of California at Berkeley for studying electromechanics of atomically thin crystals, and then stayed for one and half a year as a post-doctoral researcher developing novel optical spectroscopy for phonons, the quantized lattice vibration. Dr. Zhu started his Emerging Quantum and Ultrafast Activity Laboratory (EQUAL) in the Department of Materials Science and NanoEngineering at Rice University in July 2018.