Qimiao Si I Topology and Electron Correlations

Electrons in a crystal behave as waves that interfere with one another. Accordingly, an electronic system can have non-trivial properties when viewed through the lens of topology. At the same time, the electrons also exist as charged particles that repel one another, which raises the question of whether strong electrostatic interactions can cooperate with the wave nature of the electrons to produce correlated topological matter. For insulators, the answer is long known in affirmative as exemplified by the fractional quantum Hall effect. In the case of metallic systems, however, the question is open and pressing. 

In this talk, I will describe the route we have taken from certain canonical correlation physics to metallic topology. I’ll show how correlation effects in the form of Kondo interactions produce emergent excitations that are subjected to the constraints of crystalline symmetry, leading to Weyl-Kondo semimetals [1,2]. The materials realization [2,3] and experimental observations [2] will also be summarized. Some implications about topology and correlation physics in general will be discussed.

[1] H.-H. Lai, S. E. Grefe et al., PNAS 115, 93 (2018). https://doi.org/10.1073/pnas.1715851115

[2] S. Dzsaber et al., PNAS 118, e2013386118 (2021). https://doi.org/10.1073/pnas.2013386118

[3] L. Chen et al, Nature Physics 18, 1341 (2022). https://doi.org/10.1038/s41567-022-01743-4