Robustness of semimetallic transport properties of TaAs against off-stoichiometric disorder

TaAs single crystals were grown by a standard chemical vapor transport method. The single-crystallinity and homogeneous distribution of elements were confirmed by transmission electron microscope and x-ray diffraction observations. Positron annihilation measurements revealed that the atomic vacancy concentration was kept below 10 - 5 at. %. However, inductively coupled plasma analysis showed an As-deficient (7-9 at. %) off-stoichiometry. First-principles calculations implied that the off-stoichiometry could be compensated for with excess Ta antisite defects, thereby inducing metallic states. Nevertheless, excellent semimetallic transport properties of a well-suppressed carrier density ( ? 10 (18) cm (- 3)), ultrahigh carrier mobility ( ? 10 (6 )cm (2)/V/s), and large transverse magnetoresistance ( > 200 000% at 9 T) with the quantum oscillation were obtained at 1.7 K. This indicated the robustness of semimetallic transport properties against the off-stoichiometric disorder and the quenching of metallic conduction associated with excess Ta atoms. The negative longitudinal magnetoresistance, which is considered evidence of a Weyl semimetal (chiral anomaly), was not observed. These data were discussed with theoretical calculations.