Evolution of the electronic structure of the Weyl semimetal TaAs under pressure

Weyl semimetals provide ideal condensed matter platform to study Weyl fermions. When current and magnetic field are parallel in such systems, the chiral anomaly is expected to induce a negative longitudinal magnetoresistance. To observe this special feature the Fermi level must be close to the band crossing points (Weyl nodes) where quasiparticles behave like Weyl fermions [1].

We studied whether hydrostatic pressure can tune the Weyl node energy in TaAs closer to the Fermi level by the Shubnikov-de Haas effect at pressures up to 2.5 GPa. Analysis of the quantum oscillations (QO) showed that the big electron and hole Fermi surface pockets in TaAs are shrinking in size by 40% while the small electron pocket does not. Therefore some of the Weyl nodes are moving closer to the Fermi level with pressure.

Two-band model fits of the magnetoconductivity reveal that the electron and hole densities and mobilities in TaAs do not show a significant evolution with pressure. This seeming disagreement with QO can be explained by the smaller electron pocket being probably the main contributor to the magnetoresistance in TaAs. Our experimental data are further supplemented by theoretical calculations.

[1] A. Johansson et al., PRB 99, 075114 (2019)