Abstract
Weyl semimetals are a class of materials that can be regarded as three-dimensional analogs of graphene breaking time reversal or inversion symmetry. Electrons in a Weyl semimetal behave as Weyl fermions, which have many exotic properties, such as chiral anomaly and magnetic monopoles in the crystal momentum space. The surface state of a Weyl semimetal displays pairs of entangled Fermi arcs at two opposite surfaces. However, the existence of Weyl semimetals has not yet been proved experimentally. Here we report the experimental realization of a Weyl semimetal in TaAs by observing Fermi arcs formed by its surface states using angle-resolved photoemission spectroscopy. Our first-principles calculations, matching remarkably well with the experimental results, further confirm that TaAs is a Weyl semimetal.
Highlights
The subjects of high-energy physics and condensed-matter physics are very different, they sometimes share the same ideas
Weyl semimetals are a class of materials that can be regarded as three-dimensional analogs of graphene upon breaking time-reversal or inversion symmetry
Weyl fermions, which have not yet been discovered in high-energy physics, can be realized as an emergent phenomenon by breaking either time-reversal symmetry or inversion symmetry in Dirac semimetals, where a Dirac node can be regarded as two Weyl nodes with opposite chirality overlapping each other [Fig. 1(a)]
Summary
High-quality TaAs single crystals were grown by the chemical vapor transport method. A polycrystalline sample was filled in a quartz ampoule using iodine as a transporting agent of 2 mg=cm. The ampoule was kept at the growth temperature for three weeks. Large polyhedral crystals with dimensions up to 1.5 mm were obtained in a temperature field of ΔT 1⁄4 1150 °C–1000 °C. The as-grown crystals were characterized by x-ray diffraction using the PANalytical diffractometer with Cu Kα radiation at room temperature. The crystal growth orientation is determined by single-crystal x-ray diffraction, and the average stoichiometry was determined by energy-dispersive x-ray spectroscopy. ARPES measurements were performed at the “Dreamline” beamline of the Shanghai Synchrotron Radiation Facility (SSRF) with a Scienta D80 analyzer. The ARPES data were collected using linearly horizontal-polarized lights with a vertical analyzer slit
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