PT  - JOURNAL ARTICLE
AU  - Xu, Su-Yang
AU  - Belopolski, Ilya
AU  - Alidoust, Nasser
AU  - Neupane, Madhab
AU  - Bian, Guang
AU  - Zhang, Chenglong
AU  - Sankar, Raman
AU  - Chang, Guoqing
AU  - Yuan, Zhujun
AU  - Lee, Chi-Cheng
AU  - Huang, Shin-Ming
AU  - Zheng, Hao
AU  - Ma, Jie
AU  - Sanchez, Daniel S.
AU  - Wang, BaoKai
AU  - Bansil, Arun
AU  - Chou, Fangcheng
AU  - Shibayev, Pavel P.
AU  - Lin, Hsin
AU  - Jia, Shuang
AU  - Hasan, M. Zahid
TI  - Discovery of a Weyl fermion semimetal and topological Fermi arcs
AID  - 10.1126/science.aaa9297
DP  - 2015 Aug 07
TA  - Science
PG  - 613--617
VI  - 349
IP  - 6248
4099  - http://science.sciencemag.org/content/349/6248/613.short
4100  - http://science.sciencemag.org/content/349/6248/613.full
SO  - Science2015 Aug 07; 349
AB  - Weyl fermions—massless particles with half-integer spin—were once mistakenly thought to describe neutrinos. Although not yet observed among elementary particles, Weyl fermions may exist as collective excitations in so-called Weyl semimetals. These materials have an unusual band structure in which the linearly dispersing valence and conduction bands meet at discrete “Weyl points.” Xu et al. used photoemission spectroscopy to identify TaAs as a Weyl semimetal capable of hosting Weyl fermions. In a complementary study, Lu et al. detected the characteristic Weyl points in a photonic crystal. The observation of Weyl physics may enable the discovery of exotic fundamental phenomena.Science, this issue p. 613 and 622A Weyl semimetal is a new state of matter that hosts Weyl fermions as emergent quasiparticles and admits a topological classification that protects Fermi arc surface states on the boundary of a bulk sample. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of a Weyl semimetal, tantalum arsenide (TaAs). Using photoemission spectroscopy, we directly observe Fermi arcs on the surface, as well as the Weyl fermion cones and Weyl nodes in the bulk of TaAs single crystals. We find that Fermi arcs terminate on the Weyl fermion nodes, consistent with their topological character. Our work opens the field for the experimental study of Weyl fermions in physics and materials science.