Colloquium – Yu Li – The Pursuit of Emergent Phenomena in Quantum Materials

Speaker: Dr. Yu Li (Argonne National Laboratory)

Title: The Pursuit of Emergent Phenomena in Quantum Materials- a Perspective from Interaction, Geometry and Symmetry

Abstract:

Discovering and investigating emergent phenomena in quantum materials is an exciting and challenging endeavor, requiring careful consideration and treatment of the large number of degrees of freedom inherent in condensed matter. In this presentation, I will discuss three disparate materials which exemplify how electron correlations, geometry and symmetry affect the static and dynamical electronic and magnetic properties of solids. First, I will discuss LiFeAs, which exhibits the cooperative quantum electronic state of superconductivity. Here, the magnetic excitations, thought to be critical to the mechanism of superconductivity, exhibit exotic orbital differentiation due to the multi-orbital nature and the presence of Hund’s coupling. Second, I will discuss how geometry, in this case a pentagonal environment which frustrates long-range magnetic order in Bi2Fe4O9, leads to short-range magnetic order which is remarkably tunable. Finally, I will introduce how symmetry leads to topological electronic and magnetic properties in Cr11Ge19. Here a topological Hall effect revealed that skyrmions and anti-skyrmions may arise due to the competition between magnetic dipolar interactions and the Dzyaloshinskii-Moriya interaction on a non-centrosymmetric lattice. These results have demonstrated the success of these strategies in discovering emergent phenomena, and are inspiring further experimental efforts that combine interaction, geometry and symmetry in quantum materials