Gate-tunable negative longitudinal magnetoresistance in the predicted type-II Weyl semimetal WTe2.

Yaojia Wang,Junwen Zeng,Kang Xu,Baigeng Wang,Longqiang Zhang,Yiming Pan,Erfu Liu,Feng Miao,Zhong Huang,Dingyu Xing,Miao Wang,Huimei Liu,Xiangang Wan,Zhenlin Wang,Yajun Fu,Hai-Zhou Lu

doi:10.1038/ncomms13142

Abstract

The progress in exploiting new electronic materials has been a major driving force in solid-state physics. As a new state of matter, a Weyl semimetal (WSM), in particular a type-II WSM, hosts Weyl fermions as emergent quasiparticles and may harbour novel electrical transport properties. Nevertheless, such a type-II WSM material has not been experimentally observed. In this work, by performing systematic magneto-transport studies on thin films of a predicted material candidate WTe2, we observe notable negative longitudinal magnetoresistance, which can be attributed to the chiral anomaly in WSM. This phenomenon also exhibits strong planar orientation dependence with the absence along the tungsten chains, consistent with the distinctive feature of a type-II WSM. By applying a gate voltage, we demonstrate that the Fermi energy can be in-situ tuned through the Weyl points via the electric field effect. Our results may open opportunities for implementing new electronic applications, such as field-effect chiral devices.

Highlights

The progress in exploiting new electronic materials has been a major driving force in solid-state physics
The type-II Weyl semimetal (WSM) was recently proposed as a new type of WSM with Weyl points appearing at the boundary of electron and hole pockets[32,33,34,35,36]
We further demonstrate that by applying a gate voltage, the Fermi energy of such a material can be effectively tuned through the Weyl points; the unique transport properties can be controlled, suggesting possible applications in future chiral electronics

Summary

Results

The negative longitudinal MR observed in our samples is not as temperature sensitive as the WAL effect (see Supplementary Fig. 3), suggesting it is not related to the defect-induced weak localization effect Another theoretical work[51,52] predicting that certain impurities could induce negative longitudinal MR at small magnetic fields can be a8. For all four studied samples under similar conditions (exfoliated from the same batch of single crystals and in the identical thickness range) but different current orientation parallel to the a axis (the tungsten chains), only positive longitudinal MR was observed (see Supplementary Fig. 6)

40 V 20 V 0 V –20 V –40 V

Discussion

Methods