Fig. 1.

Weyl fermions and quantum limit transport in TaAs. a the Weyl semimetal TaAs contains three types of charge carriers: trivial holes (red), and two sets of electron-like Weyl fermions, designated W1 and W2, one of which is shown here in blue. The holes are of a single non-chiral carrier type, and contribute a non-Weyl background signature to experiments. The Weyl electrons are separated into distinct right and left-handed chiralities: arrows indicate the winding of the pseudospin around each Fermi surface. b Resistivity of TaAs for $\mathbf{J}\mid \mid \mathbf{B}\mid \mid \mathbf{c}$ from 0.7 to 20 K. Quantum oscillations from the Weyl pockets are visible up to 7.5 T, followed by a decrease and then saturation of ρ_zz up to 50 T. Above 50 T there is a two order-of-magnitude increase in ρ_zz at low temperature, signifying the opening of a gap. The inset shows single-crystal TaAs microstructured using focused-ion-beam (FIB) lithography for both the ρ_zz and ρ_xx measurements