In this talk, I will present two of our recent studies where we have used scattering methods with neutrons and resonant X-rays as probing particles. By performing pixel-power-enabled mapping-styled measurements, which provide data coverage in the three-dimensional reciprocal space plus an extra dimension in energy or real time, we have obtained unprecedented insights into magnetically and charge-ordered systems.

In the first study, we establish the existence of magnon topological “semimetal” bands (with Dirac points) in a spin-1/2 antiferromagnet, Cu3TeO6, which turns out to be surprisingly “classical” in its magnetism because of long-range exchange interactions. The demonstrated topological band structure is new to the zoo of band topology.

In the second study, we take a very close look at the birth of charge density waves (CDW) in a prototypical Peierls CDW material, ZrTe3. We demonstrate a new and rigorous route to differentiate incipient CDW against electronic standing waves, also known as Friedel oscillations (FO). Our result reveals that the CDW formation is actually promoted by self-amplifying FO, and it brings new insights to related phenomena in cuprate high-Tc superconductors.

About the speaker:  Dr. Yuan Li obtained his B.S. degrees from Peking University in 2004 and Ph.D. degree from Stanford University in 2010. From 2010 to 2012, he was a Humboldt Fellow at the Max Planck Institute for Solid State Research, Germany. He is currently an associate professor at the International Center for Quantum Materials, Peking University. Dr. Li’s research interests include phase behaviors and elementary excitations in correlated-electron materials. To determine these fundamental properties, his group uses a broad range of scattering methods including neutron and X-ray scattering at public facilities, as well as in-house Raman spectroscopy.