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SUMMARY:On Choosing a Physically Meaningful Topological Classification for
  Non-Hermitian Systems - Dr Max Lein (Tohoku University)
DTSTART:20200828T094000Z
DTEND:20200828T100000Z
UID:TALK150541@talks.cam.ac.uk
CONTACT:Joseph Nelson
DESCRIPTION:The topological classification of hermitian operators is solel
 y determined by the presence or absence of certain discrete symmetries. No
 n-hermitian systems not only admit more types of discrete symmetries\, the
 ir spectrum is a subset of the complex plane. Hence\, spectral gaps come i
 n two flavors and we in addition need to specify whether we are dealing wi
 th a point gap (co-dimension 2) or a line gap (co-dimension 1). Since the 
 presence of a line gap implies the existence of a point gap\, there is usu
 ally more than one mathematical classification of a physical system. To de
 cide which classification is physically meaningful\, I propose a simple ph
 ysical criterion based on the notion of _physically relevant states_. This
  generalizes of the notion of Fermi projection\, which even in the hermiti
 an case not determines the topological bulk classification of fermionic co
 ndensed matter systems\, but enters as an auxiliary quantity in the topolo
 gical classification of photonic and magnonic crystals. A crucial point in
  my investigation is the relevance of diagonalizability in topological cla
 ssifications\, i. e. the absence of Jordan blocks. \n\n*This talk will be 
 held online using Zoom. Please "register your email address here":https://
 forms.gle/9Rpf2BekocwLpmHD9 to receive Zoom links via email.*\n\n*Workshop
  website*: https://www.mtg.msm.cam.ac.uk/events/msm-aimr-joint-online-work
 shop-2020
LOCATION:Online - Zoom
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