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DTSTART;TZID=America/New_York:20221102T090000
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UID:10001137-1667379600-1667383200@cmsa.fas.harvard.edu
SUMMARY:Optical axion electrodynamics
DESCRIPTION:Topological Quantum Matter Seminar \nSpeaker: Junyeong Ahn (Harvard) \nTitle: Optical axion electrodynamics \nAbstract: Electromagnetic fields in a magneto-electric medium behave in close analogy to photons coupled to the hypothetical elementary particle\, the axion. This emergent axion electrodynamics is expected to provide novel ways to detect and control material properties with electromagnetic fields. Despite having been studied intensively for over a decade\, its theoretical understanding remains mostly confined to the static limit. Formulating axion electrodynamics at general optical frequencies requires resolving the difficulty of calculating optical magneto-electric coupling in periodic systems and demands a proper generalization of the axion field. In this talk\, I will introduce a theory of optical axion electrodynamics that allows for a simple quantitative analysis. Then\, I will move on to discuss the issue of the Kerr effect in axion antiferromagnets\, refuting the conventional wisdom that the Kerr effect is a measure of the net magnetic moment. Finally\, I will apply our theory to a topological antiferromagnet MnBi2Te4. \nReferences:\n[1] Theory of Optical Axion Electrodynamics\, J. Ahn\, S.Y. Xu\, A.Vishwanath\, arXiv:2205.06843
URL:https://cmsa.fas.harvard.edu/event/tqms_1122/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Topological Quantum Matter Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Topological-Seminar-11.2.22.png
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DTSTART;TZID=America/New_York:20221102T124500
DTEND;TZID=America/New_York:20221102T134500
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CREATED:20230817T174336Z
LAST-MODIFIED:20240121T174258Z
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SUMMARY:Doping and inverting Mott insulators on semiconductor moire superlattices
DESCRIPTION:Speaker: Liang Fu (MIT) \n\n\nTitle: Doping and inverting Mott insulators on semiconductor moire superlattices \nAbstract: Semiconductor bilayer heterostructures provide a remarkable platform for simulating Hubbard models on an emergent lattice defined by moire potential minima. As a hallmark of Hubbard model physics\, the Mott insulator state with local magnetic moments has been observed at half filling of moire band. In this talk\, I will describe new phases of matter that grow out of the canonical 120-degree antiferromagnetic Mott insulator on the triangular lattice. First\, in an intermediate range of magnetic fields\, doping this Mott insulator gives rise to a dilute gas of spin polarons\, which form a pseudogap metal. Second\, the application of an electric field between the two layers can invert the many-body gap of a charge-transfer Mott insulator\, resulting in a continuous phase transition to a quantum anomalous Hall insulator with a chiral spin structure. Experimental results will be discussed and compared with theoretical predictions.
URL:https://cmsa.fas.harvard.edu/event/collquium-11222/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Colloquium-11.02.22.png
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