Pressure tuning of the electrical transport properties in the Weyl semimetal TaP

We investigated the pressure evolution of the electrical transport in the almost compensated Weyl semimetal TaP. In addition, we obtained information on the modifications of the Fermi-surface topology with pressure from the analysis of pronounced Shubnikov–de Haas (SdH) quantum oscillations present in the Hall-effect and magnetoresistance data. The simultaneous analysis of the Hall and longitudinal conductivity data in a two-band model revealed an only weak decrease in the electron and hole charge-carrier densities up to 1.2 GPa, while the mobilities are essentially pressure independent along the $a$ direction of the tetragonal crystal structure. Only weak changes in the SdH frequencies for $B\parallel a$ and $B\parallel c$ point at a robust Fermi-surface topology. In contrast to the stability of the Fermi-surface topology and of the density of charge carriers, our results evidence a strong pressure variation of the magnitude of transverse magnetoresistance for $B\parallel a$ contrary to the results for $B\parallel c$. We can relate the former to an increase in the charge-carrier mobilities along the crystallographic $c$ direction.

Figure 1

Transverse magnetoresistance of TaP for the two measurement configurations (a) and (b) $B\parallel c$ and (c) and (d) $B\parallel a$ at room temperature and 2 K, respectively. In all experiments the electric current was applied perpendicular to the magnetic field and in parallel to the crystallographic $a$ axis.

Figure 2

Magnetic-field dependence of the Hall conductivity ${\sigma }_{xy}$ in the $B\parallel c$ configuration for TaP for different temperatures at (a) ambient pressure and (b) at 1.2 GPa.

Figure 3

(a) Longitudinal electrical conductivity ${\sigma }_{xx}$ and (b) Hall conductivity ${\sigma }_{xy}$ of TaP for $B\parallel c$ at 0, 0.5, and 1.2 GPa at 2 K. (c) ${\sigma }_{xx}$ and (d) ${\sigma }_{xy}$ and the corresponding fitting curves following a two-band model at 0 GPa and 2 K. See text for details. Pressure dependencies of the (e) carrier density of electrons $n_e$ and holes $n_h$ and (f) the mobility of electrons ${\mu }_e$ and holes ${\mu }_h$ along the crystallographic $a$ direction obtained from the fits.

Figure 4

Fast-Fourier transform of the Shubnikov–de Haas oscillations as a function of the inverse magnetic field taken at different pressures for (a) $B\parallel a$ and (b) $B\parallel c$, respectively. The oscillatory part, inset in (a), was extracted by a subtraction of a third-order polynomial background. Pressure dependencies of the SdH oscillation frequencies for (c) $B\parallel a$ and (d) $B\parallel c$, respectively. The error bars have been estimated taking into account the accuracy in determining the position of the maximum and the width of the peaks. (e) Fast-Fourier transforms for $B\parallel a$ at 1.4 GPa for different temperatures. Inset: temperature dependence of the amplitudes. The dashed lines are fits of the Lifshitz-Kosevich formula to the data.

Figure 5

Band structure along the connecting line between a pair of Weyl points for (a) W1 and (b) W2. The Fermi energy is set to zero and marked by a dashed line.