Discovery of Weyl semimetal NbAs, Su-Yang Xu, Nasser Alidoust, Ilya Belopolski, Chenglong Zhang, Guang Bian, Tay-Rong Chang, Hao Zheng, Vladimir Strokov, Daniel S. Sanchez, Guoqing Chang, Zhujun Yuan, Daixiang Mou, Yun Wu, Lunan Huang, Chi-Cheng Lee, Shin-Ming Huang, BaoKai Wang, Arun Bansil, Horng-Tay Jeng, Titus Neupert, Adam Kaminski, Hsin Lin, Shuang Jia and M. Zahid Hasan
We report the discovery of Weyl semimetal NbAs featuring unusual Fermi arc surface states.
Three types of Fermions play a fundamental role in our understanding of nature: Dirac, Majorana, and Weyl. While Dirac fermions are known, the latter two have not been observed as any fundamental particle in high energy physics and have emerged as a much-sought-out treasure in condensed matter physics. A Weyl semimetal is a novel crystal whose low-energy electronic excitations behave as Weyl fermions. It has received worldwide interest and is believed to open the next era of condensed matter physics after graphene and three-dimensional topological insulators.
However, experimental research has been held back because Weyl semimetals are extremely rare in nature. Here, we present the experimental discovery of the Weyl semimetal state in niobium arsenide (NbAs). Utilizing the combination of soft X-ray and ultraviolet photoemission spectroscopy,
we systematically study both the surface and bulk electronic structure of NbAs. We experimentally observe both the Weyl cones and Weyl nodes in the bulk and the Fermi arcs on the surface of this system. Our ARPES data, in agreement with our previous theoretical prediction and present band structure calculations, provide conclusive evidence for the topological Weyl semimetal state in NbAs. Our discovery not only paves the way for the many fascinating topological quantum phenomena predicted in Weyl semimetals, but also establishes a new cornerstone in the correspondence between high-energy and condensed matter physics.
Ok then, the revolution will be televised in quantum holography.
Hasan is really tearing it up.
See the original theory paper here: http://arxiv.org/abs/1501.00755
An inversion breaking Weyl semimetal state in the TaAs material class, Shin-Ming Huang, Su-Yang Xu, Ilya Belopolski, Chi-Cheng Lee, Guoqing Chang, BaoKai Wang, Nasser Alidoust, Guang Bian, Madhab Neupane, Arun Bansil, Hsin Lin and M. Zahid Hasan
The recent discoveries of Dirac fermions in graphene and on the surface of topological insulators have ignited worldwide interest in physics and materials science. A Weyl semimetal is an unusual crystal where electrons also behave as massless quasi-particles but interestingly they are not Dirac fermions. These massless particles, Weyl fermions, were originally considered in massless quantum electrodynamics but have not been observed as a fundamental particle in nature. A Weyl semimetal provides a condensed matter realization of Weyl fermions, leading to unique transport properties with novel device applications. Such a semimetal is also a topologically non-trivial metallic phase of matter extending the classification of topological phases beyond insulators. The signature of a Weyl semimetal in real materials is the existence of unusual Fermi arc surface states, which can be viewed as half of a surface Dirac cone in a topological insulator. Here, we identify the first Weyl semimetal in a class of stoichiometric materials, which break crystalline inversion symmetry, including TaAs, TaP, NbAs and NbP. Our first-principles calculations on TaAs reveal the spin-polarized Weyl cones and Fermi arc surface states in this compound. We also observe pairs of Weyl points with the same chiral charge which project onto the same point in the surface Brillouin zone, giving rise to multiple Fermi arcs connecting to a given Weyl point. Our results show that TaAs is the first topological semimetal identified which does not depend on fine-tuning of chemical composition or magnetic order, greatly facilitating an exploration of Weyl physics in real materials.