Fermi Surface Topology and Transport in Weyl Semimetals

Weyl Fermions are the solution of the massless Dirac equations and have been long sought after in high energy physics [1]. Weyl semimetals host quasiparticles that can be described as Weyl electrons. Recently the non-centrosymmetric mono-pnictides (Ta,Nb)(P,As) were predicted to be Weyl semimetals by ab initio DFT calculations [2]. The presence of Weyl nodes and Fermi arc surface states in these materials was later confirmed by ARPES [3]. Here, we present the precise Fermi surface topography of our TaP and TaAs single crystals as determined by quantum oscillation measurements and ab intio bandstructure calculations. It will be shown that chirality in TaP is ill-defined [4]. In TaAs, on the other hand, well-defined Weyl pockets of opposite chirality exist [5]. Thus quantum phenomena due to chirality are only expected in TaAs. As a second point, we also show evidence that experimental results of the longitudinal magnetoresistance in these compounds can easily be dominated by effects of a field-induced resistance anisotropy. In that case, current inhomogeneities [6] can lead to an apparent “negative magnetoresistance” as expected for the chiral anomaly [7].

[1] H. Weyl, Zeitschrift f. Physik 56, 330 (1929)
[2] H. Weng et al., Phys. Rev. X 5, 011029 (2015)
[3] B. Q. Lv et al., Phys. Rev. X 5, 031013 (2015), S.-Y. Xu et al. Science 349, 613 (2015)
[4] F. Arnold et al., Nat. Comm. 7, 11615 (2016)
[5] F. Arnold et al., Phys. Rev. Lett. 117, 146401 (2016)
[6] K. Yoshida, JPSJ 41, 574 (1975)
[7] R. Dos Reis et al., NJP 18, 085006 (2016)