Spin Polarization and Texture of the Fermi Arcs in the Weyl Fermion Semimetal TaAs

Su-Yang Xu, Ilya Belopolski, Daniel S. Sanchez, Madhab Neupane, Guoqing Chang, Koichiro Yaji, Zhujun Yuan, Chenglong Zhang, Kenta Kuroda, Guang Bian

Abstract

A Weyl semimetal is a new state of matter that hosts Weyl fermions as quasiparticle excitations. The Weyl fermions at zero energy correspond to points of bulk-band degeneracy, called Weyl nodes, which are separated in momentum space and are connected only through the crystal's boundary by an exotic Fermi arc surface state. We experimentally measure the spin polarization of the Fermi arcs in the first experimentally discovered Weyl semimetal TaAs. Our spin data, for the first time, reveal that the Fermi arcs' spin-polarization magnitude is as large as 80% and lies completely in the plane of the surface. Moreover, we demonstrate that the chirality of the Weyl nodes in TaAs cannot be inferred by the spin texture of the Fermi arcs. The observed nondegenerate property of the Fermi arcs is important for establishing its exact topological nature, which reveals that spins on the arc form a novel type of 2D matter. Additionally, the nearly full spin polarization we observed (∼80%) may be useful in spintronic applications.Received 29 October 2015DOI:https://doi.org/10.1103/PhysRevLett.116.096801© 2016 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFermi surfaceSpin polarizationWeyl fermionsTechniquesAngle-resolved photoemission spectroscopyCondensed Matter, Materials & Applied Physics

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