Origin of planar Hall effect in type-II Weyl semimetal MoTe2

D D Liang,W K Zhu,S R Weng,X Yan,J Yang,L Pi,W Tong,C J Zhang,Y J Wang,W L Zhen,Y Y Han

doi:10.1063/1.5094231

Abstract

Besides the negative longitudinal magnetoresistance (MR), planar Hall effect (PHE) is a newly emerging experimental tool to test the chiral anomaly or nontrivial Berry curvature in Weyl semimetals (WSMs). However, the origins of PHE in various systems are not fully distinguished and understood. Here we perform a systematic study on the PHE and anisotropic MR (AMR) of Td-MoTe2, a type-II WSM. Although the PHE and AMR curves can be well fitted by the theoretical formulas, we demonstrate that the anisotropic resistivity arises from the orbital MR (OMR), instead of the negative MR as expected in the chiral anomaly effect. In contrast, the positive MR indicates that the large OMR dominates over the chiral anomaly effect. This explains why it is difficult to measure negative MR in type-II WSMs. We argue that the measured PHE can be related with the chiral anomaly only when the negative MR is simultaneously observed.

Highlights

The planar Hall effect (PHE) and anisotropic MR (AMR) curves can be well fitted by the theoretical formulas, we demonstrate that the anisotropic resistivity arises from the orbital MR (OMR), instead of the negative MR as expected in the chiral anomaly effect
The PHE and AMR curves can be well fitted by the theoretical formulas, we demonstrate that the anisotropic resistivity ∆ρ arises from the OMR that increases the ρ more quickly, instead of the reduced ρ∥ as expected in the chiral anomaly effect, which is distinctly different from Ref. 20
The positive LMR indicates that the large OMR dominates over the chiral anomaly effect

Summary

Introduction

Weyl fermions in condensed matter systems represent the linearly dispersing low-energy excitations that obey a two-component Dirac equation. Different from the type-I Weyl semimetals (WSMs, materials hosting Weyl fermions) which have standard Weyl points with a point-like Fermi surface, the type-II WSMs possess tilted Weyl points, arising at the contact of electron and hole pockets. The orthorhombic phase (Td) of layered transition metal dichalcogenides WTe2 and MoTe2 are theoretically predicted as the potential candidates for the type-II WSMs. Signatures of Fermi arcs, the surface state of WSMs, have been observed in the angle-resolved photoemission spectroscopy (ARPES) measurements for WTe24,5 and MoTe2.6,7In transport experiments, WSMs are usually featured for the negative longitudinal magnetoresistance (NLMR) induced by chiral anomaly, which refers to the non-conservation of chiral charge around the Weyl nodes when the applied electric and magnetic fields are non-orthogonal (E ⋅ B ≠ 0). The orthorhombic phase (Td) of layered transition metal dichalcogenides WTe2 and MoTe2 are theoretically predicted as the potential candidates for the type-II WSMs.. Signatures of Fermi arcs, the surface state of WSMs, have been observed in the angle-resolved photoemission spectroscopy (ARPES) measurements for WTe24,5 and MoTe2.6,7. WSMs are usually featured for the negative longitudinal magnetoresistance (NLMR) induced by chiral anomaly, which refers to the non-conservation of chiral charge around the Weyl nodes when the applied electric and magnetic fields are non-orthogonal (E ⋅ B ≠ 0). The experimental measurement of NLMR is very critical, and especially for type-II WSMs, the NLMR can only be observed along specific crystalline directions and in samples with appropriate chemical potential In the pure Weyl physics, the NLMR will induce non-zero off-diagonal components under the SO (3) rotation transformation, further leading to a planar Hall effect (PHE)..

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Conclusion