Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 113, Issue 31, Pages 8648-8652Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1524787113
Keywords
Dirac semimetals; Weyl semimetals; topological insulator; Fermi arcs
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Funding
- Center for Emergent Materials (CEM), a National Science Foundation (NSF) Material Research Science and Engineering Center (MRSEC) [DMR-1420451]
- NSF [DMR-1410364, PHY-1066293]
- Ohio State University
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1410364] Funding Source: National Science Foundation
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Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, inmarked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at k =(0,0, +/- Q), where gapless states on the side surfaces are protected only near k(z) = 0. We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2. Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments.
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