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. Hanyu Zhu is an assistant professor of Materials Science and NanoEngineering at Rice University. He earned his B.S. in Mathematics and Physics in Tsinghua University in China, when he got into the field of nanomaterials. He obtained his Ph.D. in Applied Science and Technology in the University of California at Berkeley for studying electromechanics of atomically thin crystals. After the postdoctoral research at Berkeley developing novel optical spectroscopy for phonons, he started the Emerging Quantum and Ultrafast materials Lab in 2018, with a focus on quantum control of low dimensional and correlated materials. In 2019 he received the ORAU Ralph E. Powe Junior Faculty Enhancement Award. From 2020 he held jointly appointment in the department of Physics and Astronomy, and became part of the Rice Center for Quantum Materials, as well as the Rice Quantum Initiative.