How Excitons Met Topology

by Ryo Mori (University of Tokyo)

Thursday 29 Feb 2024, 11:00 → 12:00 America/Los_Angeles

48/2-224 - Madrone (SLAC)

 

 The exciton, a bound state of an electron and a hole, is a fundamental quasiparticle induced by coherent light-matter interactions in semiconductors. Such Coulomb-bound states have gained significant interest due to their critical roles in both fundamental science and technological applications. Concurrently, recent advancements in the study of topological phases of matter have shed light on new routes in materials science, leading to the discovery of unique phases and properties, such as spin-polarized surface states in topological insulators. One of the ultimate frontiers in these fields is to create excitonic states coupled with topological quasiparticles, to leverage both topological effects and excitonic correlations simultaneously. However, numerous questions remain, particularly regarding whether excitonic states can be induced in the presence of topological invariants, how these properties manifest in the material’s electronic structures, and what properties of the topological states persist. In this talk, I will present our recent work[1], which reports the direct observation of excitonic states in a topological insulator measured by ultrafast angle-resolved photoemission spectroscopy. This work reveals the conditions under which excitonic states can be driven in topological insulators, as well as the unique excitonic signatures that emerge in topological states and the topological signatures induced in the excitonic states. Future directions for exploring and manipulating the excitonic topological states will also be discussed. This research opens up a new platform for probing exciton-mediated states in topological materials and investigating their potential applications.  
 

see:   R. Mori  et al., Nature 614, 249 (2023)

Slides     Zoom recording.   (the seminar begins at 00:16:30)

 

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