Quantum oscillation study of the large magnetoresistance in Ta-doped WTe₂ single crystals

In recent years, a wide range of topological materials, including topological insulators and semimetals, have been discovered. Among them, semimetals have attracted substantial research attention due to their unique electronic properties. Materials exhibiting large magnetoresistance (MR), where the electrical resistance changes drastically under an applied magnetic field, play a crucial role in modern electronic technologies such as magnetic sensors and data storage devices. The discovery of extremely large MR in tungsten ditelluride (WTe₂) has renewed significant interest in this material. Notably, WTe₂ has also been reported to exhibit superconductivity under high pressure and is predicted to be a type-II Weyl semimetal, as confirmed by angle-resolved photoemission spectroscopy (ARPES). The exceptionally high MR in WTe₂ originates from nearly perfect electron-hole compensation and high carrier mobility.

In this work, high-quality single crystals of WTe₂ were successfully synthesized, exhibiting an exceptionally large magnetoresistance (MR) of 23282% at 2 K under a 6.5 T field. The quadratic field dependence confirms its nature as a perfectly compensated semimetal. Resistivity measurements exhibit metallic behavior without any magnetic transition between 2 and 300 K, governed by electron–electron scattering at low temperatures and electron–phonon scattering at higher temperatures. Clear Shubnikov-de Haas (SdH) oscillations with a nonzero Berry phase confirm the presence of topological states, while an anisotropy factor of ~1.4 reflects the directional dependence of transport, consistent with previous reports on anisotropic magnetoresistance in WTe2 [Phys. Rev. B 92, 041104 (2015)]. Furthermore, we observe that tantalum (Ta) substitution results in a decrease in MR, despite improved charge compensation, indicating that the suppression originates from a reduction in carrier mobility rather than charge imbalance. The nearly unchanged effective masses suggest that scattering-induced mobility degradation, rather than band-structure modification, governs the MR behavior. These results provide deeper insight into the interplay of anisotropy, mobility, and compensation in topological semimetals.