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IQIM Postdoctoral and Graduate Student Seminar

Friday, January 19, 2024
12:00pm to 1:00pm
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East Bridge 201 (Richard P. Feynman Lecture Hall)
Magic Angles and Fractional Chern Insulators in Twisted Homobilayer TMDs
Allan MacDonald, Sid W. Richardson Foundation Regents Chair in Physics, University of Texas at Austin,

Abstract: Recent experiments [1, 2] have reported the first observations of fractional Chern insulators (FCIs), exotic states of matter that display a fractional quantum Hall effect in the absence of a magnetic field. The FCIs were discovered in the hole fluids of AA-stacked K-valley transition metal dichalcogenide (TMD) twisted homobilayers. Earlier theoretical work had hinted that FCI states might appear in systems of this type by showing that their moiré minibands could carry Chern numbers [3], that the moiré band width could mysteriously vanish [4] near a magic twist angle, and that the bands have almost ideal quantum geometry [5] when flat. I will explain [6] the appearance of magic angle flat bands and FCIs in these systems by mapping their continuum model to a Landau level problem, and use this framework to discuss optical signatures of FCI states and competitions between FCI and CDW gapped insulating states.

[1] J. Cai et al., Signatures of fractional quantum anomalous hall states in twisted MoTe2, Nature (2023).

[2] Y. Zeng et al., Integer and fractional chern insulators in twisted bilayer MoTe2, Nature (2023).

[3] F. Wu et al. Topological insulators in twisted transition metal dichalcogenide homobilayers, Phys. Rev. Lett. 122, 086402 (2019).

[4] T. Devakul et al., Magic in twisted transition metal dichalcogenide bilayers, Nature

Communications 12, 6730 (2021).

[5] N. Morales-Duran et al. Pressure–enhanced fractional chern insulators in moire transition

metal dichalcogenides along a magic line, Physical Review Research (2023).

[6] N. Morales-Duran et al., Magic Angles and Fractional Chern Insulators in Twisted Homobilayer TMDs, (2023) arXiv: 2308.03143.

Lunch will be provided, following the talk, on the lawn north of the Bridge Building.

For more information, please contact Marcia Brown by phone at 626-395-4013 or by email at [email protected].