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DTSTART;TZID=America/New_York:20221205T090000
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DTSTAMP:20260410T175812
CREATED:20240215T100106Z
LAST-MODIFIED:20240819T150452Z
UID:10002734-1670230800-1670236200@cmsa.fas.harvard.edu
SUMMARY:Exact Many-Body Ground States from Decomposition of Ideal Higher Chern Bands: Applications to Chirally Twisted Graphene Multilayers
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Junkai Dong (Harvard University) \nTitle: Exact Many-Body Ground States from Decomposition of Ideal Higher Chern Bands: Applications to Chirally Twisted Graphene Multilayers \nAbstract: Motivated by the higher Chern bands of twisted graphene multilayers\, we consider flat bands with arbitrary Chern number C with ideal quantum geometry. While C>1 bands differ from Landau levels\, we show that these bands host exact fractional Chern insulator (FCI) ground states for short range interactions. We show how to decompose ideal higher Chern bands into separate ideal bands with Chern number 1 that are intertwined through translation and rotation symmetry. The decomposed bands admit an SU(C) action that combines real space and momentum space translations. Remarkably\, they also allow for analytic construction of exact many-body ground states\, such as generalized quantum Hall ferromagnets and FCIs\, including flavor-singlet Halperin states and Laughlin ferromagnets in the limit of short-range interactions. In this limit\, the SU(C) action is promoted to a symmetry on the ground state subspace. While flavor singlet states are translation symmetric\, the flavor ferromagnets correspond to translation broken states and admit charged skyrmion excitations corresponding to a spatially varying density wave pattern. We confirm our analytic predictions with numerical simulations of ideal bands of twisted chiral multilayers of graphene\, and discuss consequences for experimentally accessible systems such as monolayer graphene twisted relative to a Bernal bilayer. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_12522/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-Seminar-12.5.22.png
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DTSTART;TZID=America/New_York:20221205T110000
DTEND;TZID=America/New_York:20221205T120000
DTSTAMP:20260410T175812
CREATED:20230730T184816Z
LAST-MODIFIED:20240110T050720Z
UID:10001156-1670238000-1670241600@cmsa.fas.harvard.edu
SUMMARY:IIB Explored - Dualities\, Bordisms\, and the Swampland
DESCRIPTION:Swampland Seminar \nLocation: Jefferson Physical Laboratory\, Seminar room J356 \nSpeaker: Markus Dierigl (LMU Munich) \nTitle: IIB Explored – Dualities\, Bordisms\, and the Swampland \nAbstract: In this talk I will discuss the application of the Cobordism Conjecture to type IIB supergravity with non-trivial duality bundle. Calculating the relevant bordism groups we find that they are highly non-trivial and would predict the presence of various global symmetries in the underlying theory. Since quantum gravity theories do not allow for global symmetries\, we discuss which defects need to be included to break them completely. Interestingly\, we find many backgrounds that are well-known in the F-theory literature\, such as [p\,q]-7-branes\, non-Higgsable clusters\, as well as S-folds and their generalizations to higher codimensions. Further including worldsheet reflections\, predicts the existence of a new non-supersymmetric 7-brane with interesting properties and applications\, which I will discuss in more detail.
URL:https://cmsa.fas.harvard.edu/event/swampland_12522/
LOCATION:Jefferson 356
CATEGORIES:Swampland Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Topological-Seminar-11.09.23.png
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