University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Tuesday, September 29th 2015
4:30 pm:
CM Journal Club in PAN 210
Speaker: Tobias Gulden
Subject: Weyl semimetals and surface Fermi arcs: an introduction
Please Note: Meeting room will be changed to PAN 210 for the rest of the semester.

Recently the experimental discovery of surface Fermi arcs in TaAs were the first proof of existence of a Weyl semimetal [1]. The existence of these states in 3 spatial dimensions was theoretically proposed before, a short summary was published in a viewpoint [2]. The characteristic surface Fermi arcs appear as a projection of Weyl points in the bulk material. A Weyl point can only appear when either time reversal or spacial inversion symmetry are broken, and when there is an accidental degeneracy of two bands [3,4]. Following [4] I will show why this degeneracy is unlikely in 2 dimensions but rather generic in 3 dimensions, and how the projection of the Weyl points onto the surface yields a structure of surface Fermi arcs. However not every surface of a Weyl semimetal contains surface arcs, if two Weyl points of opposite chirality have the same projection the surface states cancel out. As example I will discuss the structure of the 24 Weyl points in the first experimentally known Weyl semimetal, TaAs.

[1] S.-Y. Xu et al, Science 349, 6248, pp.613-617 (2015)
[2] “Viewpoint: Weyl electrons kiss”, L. Balents, Physics 4, 36 (2011)
[3] H. Weng, C. Fang, Z. Fang, B.A. Bernevig and X. Dai, PRX 5, 011029 (2015)
[4] E. Witten, lectures at Princeton summer school 2015, online at

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