Discovery of a Weyl fermion semimetal and topological Fermi arcs

By Su-Yang Xu, I. Belopolski, N. Alidoust, M. Neupane, G. Bian, Chenglong Zhang, R. Sankar, G. Chang, Zhujun Yuan, Chi-Cheng Lee and 11 more. Science, 2015

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Weyl physics emerges in the laboratory 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 622 Angle-resolved photoemission is used to detect the topological surface states and bulk dispersion of the compound tantalum arsenide. [Also see Report by Lu et al.] A 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.

Subfields: Atomic and Molecular Physics, and Optics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/194630ef465a0c6ef4a64f6dceb3c81d55315770

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Citations in the corpus

Topological Semimetals from First Principles (2018, background): “A decisive advance came in 2015, when the observation of a T -invariant Weyl semimetal phase was reported in TaAs and related materials (94, 95, 96, 97, 98, 99) based on earlier theoretical predictions (7, 33).”
Experimental observation of optical Weyl points and Fermi arc-like surface states (2016, background): “The observation of Weyl points, in microwave photonics [1] and condensed matter physics [2, 3], has attracted a great deal of attention because they constitute the simplest possible topologically-nontrivial band structure in 3D.”
Symmetry Indicators and Anomalous Surface States of Topological Crystalline Insulators (2017, neutral): “[48] Su-Yang Xu, Ilya Belopolski, Nasser Alidoust, Madhab Neu-”