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SUMMARY:Topological skyrmion phases of matter - Ashley Cook (MPI PKS Dresd
 en)
DTSTART:20220613T130000Z
DTEND:20220613T140000Z
UID:TALK175535@talks.cam.ac.uk
CONTACT:Jan Behrends
DESCRIPTION:Symmetry-protected topological phases of matter have long been
  classified based on mappings from the Brillouin zone to the space of proj
 ectors\, or flat band Hamiltonians. This is the basis of the ten fold way 
 classification scheme. Here\, we show effectively non-interacting topologi
 cal phases are associated with mappings from the Brillouin zone to the spa
 ce of other observables. We specifically consider topological phases of th
 e spin degree of freedom of the ground state\, protected by a generalized 
 particle-hole symmetry\, which are independent of the topological phases o
 f the full set of degrees of freedom of the ground state. We show these ph
 ases realize distinctive momentum-space skyrmionic spin textures\, and exh
 ibit two types of bulk-boundary correspondence. We present recipes for con
 structing toy models\, and also explore consequences of this physics in mo
 dels for transition metal oxide superconductors as the generalized particl
 e-hole symmetry occurs in centrosymmetric superconductors. When spin is no
 t conserved\, we find two kinds of topological phase transitions are possi
 ble. The second kind occurs without the closing of an energy gap while res
 pecting the symmetry protecting the topological phase\, due to the minimum
  spin magnitude becoming zero. This contradicts the flat band limit assump
 tion used to construct the ten fold way classification scheme.
LOCATION:Details of video conferencing will be distributed nearer the time
 .
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