BEGIN:VCALENDAR VERSION:2.0 PRODID:Data::ICal 0.22 BEGIN:VEVENT DESCRIPTION:Ching-Kai Chiu\, University of Maryland\n\n
\n In an ordinary three-dimensional metal the Fermi surface forms a two-dimensional closed sheet separating the filled from the empty states. Topological semimetals\ , on the other hand\, can exhibit protected one-dimensional Fermi lines or zero-dimensional Fermi points\, which arise due to an intricate interplay between symmetry and topology of the electronic wavefunctions. Here\, we study how reflection symmetry\, time-reversal symmetry\, and inversion sym metry leads to the topological protection of line nodes in three-dimension al semi-metals. We derive the Z- and Z2-type invariants that guarantee the stability of the line nodes and lead to the appearance of protected surfa ces states. As a representative example of a topological semimetal with li ne nodes\, we consider \;Ca3P2 \;and discuss the topological prope rties of its Fermi line in terms of a tight-binding model\, derived from a b initio DFT calculations. We show that due to a bulk-boundary corresponde nce\, \;Ca3P2 \;displays nearly dispersionless surface states\, wh ich take the shape of a drumhead. These topological surface states give ri se to the charge polarization.
\n DTSTART:20150903T193000Z LOCATION:Physics Building\, Room 204 SUMMARY:Topological line nodes in Ca3P2 and other semi-metals END:VEVENT END:VCALENDAR