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UID:DSC-22673
DTSTART;TZID=Europe/Berlin:20260224T110000
SEQUENCE:1771915115
TRANSP:OPAQUE
DTEND;TZID=Europe/Berlin:20260224T120000
URL:https://dresden-science-calendar.org/calendar/de/detail/22673
LOCATION:IFW\, Helmholtzstraße 2001069 Dresden
SUMMARY:König: Exceptional Fermion Doubling of Non-Hermitian Systems
CLASS:PUBLIC
DESCRIPTION:Speaker: Lukas König\nInstitute of Speaker: Stockholm Universi
 ty\nTopics:\n\n Location:\n  Name: IFW (D2E.27\, IFW Dresden)\n  Street: H
 elmholtzstraße 20\n  City: 01069 Dresden\n  Phone: \n  Fax: \nDescription
 : Nielsen and Ninomiya&amp\;#039\;s fermion doubling theorem arises from t
 he topological classification of chiral fermions in lattice systems\, mand
 ating that their total chirality across the Brillouin zone must vanish. It
  has recently been shown to break down in two distinct ways. First\, in no
 n-Hermitian systems\, the &amp\;quot\;fermions&amp\;quot\; are exceptional
  points that are topologically classified by non-Abelian braids. This comp
 licates the total chirality requirement\, leading to the possibility of mo
 nopoles. Second\, in systems with non-symmorphic symmetries\, the underlyi
 ng Brillouin zone can reduce to a non-orientable manifold\, weakening the 
 notion of chirality itself.  Using simple examples as well as homotopy the
 ory\, I will show how the classification of gapped phases has to be adapte
 d\, and what remains of fermion doubling in such systems. I will highlight
  two recent photonic experiments in which the aforementioned monopoles wer
 e observed directly. Time permitting\, I will discuss extensions of these 
 homotopy tools to more complicated problems. --- [1] König\, J. L. K. et 
 al.\, Braid-protected topological band structures with unpaired exceptiona
 l points. Phys. Rev. Res. 5\, L042010 (2023). [2] König\, J. L. K. et al.
 \, Exceptional Topology on Nonorientable Manifolds. To appear in Phys. Rev
 . Research (2026). [3] Wang\, K. et al. Observation of Braid-Protected Unp
 aired Exceptional Points. Phys. Rev. Lett. 136\, 056602 (2026). [4] Xu\, Z
 .-S. et al. Non-Hermitian Exceptional Topology on a Klein Bottle Photonic 
 Circuit. Preprint at arXiv:2512.20273. .
DTSTAMP:20260712T004351Z
CREATED:20260217T063755Z
LAST-MODIFIED:20260224T063835Z
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