Fermi surface investigation of the semimetal ${\mathrm{TaAs}}_2$

The transversal magnetoresistance associated with the semimetal ${\mathrm{TaAs}}_2$ shows a parabolic field dependence that rises unrestrictedly to 2800 at 14 T and 1.8 K. Here, we report the results of a comprehensive quantum-oscillation study. Angular-dependent de Haas–van Alphen (dHvA) data were obtained with the method of cantilever-torque magnetometry. These were compared with the results of density-functional theory calculations, which predict a Fermi surface with two kinds of electron pockets, as well as two types of hole pockets. Only the electron pockets could be experimentally verified, whereas no evidence for the hole pockets is present in the measured dHvA frequencies.

Figure 1

(a) Temperature dependence of the resistivity, at zero field and an applied field of 14 T. Inset: Log-log plot highlighting different $\rho \left(T\right)$ regimes. The green and magenta lines are guides for the eye indicating slopes of a linear and a quadratic behavior, respectively. The cyan line is a power-law fit $\rho \left(T\right)=\rho \left(0\right)+a{T}^n$ to the zero-field data below 100 K. (b) Magnetoresistance of ${\mathrm{TaAs}}_2$, expressed as $\mathrm{\Delta }\rho /\rho (B=0)$. Shubnikov–de Haas (SdH) oscillations appear at fields larger than 4 T.

Figure 2

Field-dependent torque magnetization measured close to $B\parallel \left[\overline{2}01\right]$. The inset is the enlarged low-field region in which quantum oscillations appear at approximately 0.7 T.

Figure 3

Frequency spectrum corresponding to the data of Fig. 2, obtained after polynomial background subtraction and subsequent Fourier transformation. At higher fields, up to four different frequencies are resolved.

Figure 4

Frequency spectra measured by (a) SdH at 1.8 K and (b) dHvA at 30 mK with $B\parallel \left[\overline{2}01\right]$.

Figure 5

Angular dependence of the measured (circles) and theoretical (lines) dHvA frequencies of ${\mathrm{TaAs}}_2$. The left part shows the ${90}^{\circ }$ rotation from the $b$ to the $\left[\overline{2}01\right]$ axis and the right the ${180}^{\circ }$ rotation in the $ac$ plane (see sketches illustrating the sample geometry). The grey circles indicate dHvA frequencies that could not be designated to a specific branch. Colors of the calculated frequencies correspond to the Fermi surface colors in Fig. 7.

Figure 6

Calculated band structure of ${\mathrm{TaAs}}_2$. The inset shows the first Brillouin zone with high-symmetry points. One hole band (black) and one electron band (blue) cross Fermi energy ($E_F$).

Figure 7

Calculated Fermi surface sheets of (a) hole pocket $H$, (c) electron pocket $E_1$, and (d) electron pocket $E_2$. (b) The same pocket as (a), but not restricted to the first Brillouin zone.