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Condensed Matter Seminars
Condensed Matter
Thursday, September 3, 2015
3:30 PM
Physics Building, Room 204
Note special time.
Note special room.

ChingKai Chiu
[Host: Jeffrey Teo]
University of Maryland
"Topological line nodes in Ca3P2 and other semimetals"

ABSTRACT:
In an ordinary threedimensional metal the Fermi surface forms a twodimensional closed sheet separating the filled from the empty states. Topological semimetals, on the other hand, can exhibit protected onedimensional Fermi lines or zerodimensional Fermi points, which arise due to an intricate interplay between symmetry and topology of the electronic wavefunctions. Here, we study how reflection symmetry, timereversal symmetry, and inversion symmetry leads to the topological protection of line nodes in threedimensional semimetals. We derive the Z and Z2type invariants that guarantee the stability of the line nodes and lead to the appearance of protected surfaces states. As a representative example of a topological semimetal with line nodes, we consider Ca3P2 and discuss the topological properties of its Fermi line in terms of a tightbinding model, derived from ab initio DFT calculations. We show that due to a bulkboundary correspondence, Ca3P2 displays nearly dispersionless surface states, which take the shape of a drumhead. These topological surface states give rise to the charge polarization.




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