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Phys Rev Lett. 2016 Feb 12;116(6):066802. doi: 10.1103/PhysRevLett.116.066802. Epub 2016 Feb 10.

Criteria for Directly Detecting Topological Fermi Arcs in Weyl Semimetals.

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Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
International Center for Quantum Materials, Peking University, Beijing 100871, China.
Condensed Matter and Magnet Science Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Department of Physics, University of Central Florida, Orlando, Florida 32816, USA.
Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan.
Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
Institute of Physics, Academia Sinica, Taipei 11529, Taiwan.


The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature and demonstrates a novel type of anomalous surface state, the Fermi arc. Like topological insulators, the bulk topological invariants of a Weyl semimetal are uniquely fixed by the surface states of a bulk sample. Here we present a set of distinct conditions, accessible by angle-resolved photoemission spectroscopy (ARPES), each of which demonstrates topological Fermi arcs in a surface state band structure, with minimal reliance on calculation. We apply these results to TaAs and NbP. For the first time, we rigorously demonstrate a nonzero Chern number in TaAs by counting chiral edge modes on a closed loop. We further show that it is unreasonable to directly observe Fermi arcs in NbP by ARPES within available experimental resolution and spectral linewidth. Our results are general and apply to any new material to demonstrate a Weyl semimetal.

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