Anisotropic planar Hall effect in the type-II topological Weyl semimetal ${\mathrm{WTe}}_2$

The giant planar Hall effect arising from a chiral anomaly, and that is related to the Berry curvature, has been predicted but never observed in nonmagnetic type-II Dirac/Weyl semimetals. Here, we report an observation of the anisotropic planar Hall effect in type-II Weyl semimetal ${\mathrm{WTe}}_2$. Interestingly, we observe a chiral-anomaly-induced sinusoidal angular-dependent planar Hall effect when the electric field is parallel to the tilting direction of Weyl cone, i.e., the $b$ axis of ${\mathrm{WTe}}_2$. The planar Hall effect amplitude is linearly dependent on the magnetic fields and decreases gradually as the temperature increases across the topological phase transition temperature. Our observations clearly reveal the footprints on transport from the chiral anomaly feature in type-II Weyl semimetals.

Figure 1

(a) Typical optical image of ${\mathrm{WTe}}_2$ devices. The scale bar is 10 μm. The thickness of the device is 18.4 nm. (b) Typical polarized Raman spectra with the laser polarization direction along the $a$ and $b$ axes of ${\mathrm{WTe}}_2$. Magnetic field dependence of longitudinal magnetoresistance at 2 K, with current along the $a$ axis (c) and $b$ axis (d) of ${\mathrm{WTe}}_2$. As the increase of deviation between the current and magnetic field, the negative magnetoresistance in (d) vanishes quickly. (e) Raw SdH oscillations with current along the $a$ and $b$ axes ($T=30\mathrm{mK}$). (f) FFT spectra of SdH oscillations with current along the $a$ axis (e) and $b$ axis (f) of ${\mathrm{WTe}}_2$. The arrow indicates the Weyl orbit quantum oscillation.

Figure 2

(a) Angular dependence of planar Hall resistivity of ${\mathrm{WTe}}_2$, with current along the $a$ axis (a) and $b$ axis (b), under a magnetic field of 14 T and at 2 K. Solid lines give the angular fittings of sinφ and sin2φ terms. Raw data of angular dependent planar Hall resistivity at various magnetic fields with current along the $a$ axis (c) and $b$ axis (d). Fitted planar Hall resistivity amplitude of sinφ (e) and sin2φ (f) terms as a function of the magnetic field, with current along the $a$ and $b$ axes. Solid lines give the linear and quadratic fitting for sinφ (e) and sin2φ (f) terms, respectively.

Figure 3

Measured in-plane anisotropic longitudinal resistivity of ${\mathrm{WTe}}_2$ ($t=18.4\mathrm{nm}$), under various magnetic fields, and at 2 K, (a) $E//a$ axis; (b) $E//b$ axis. Extracted longitudinal resistivity as a function of the magnetic field, (c) $E//a$ axis; (d) $E//b$ axis. The solid lines give the best fittings of ${\rho }_{\perp }$.

Figure 4

Measured angular dependence of planar Hall resistivity of ${\mathrm{WTe}}_2$ at different temperatures ($B=14\mathrm{T}$), (a) $E//a$ axis; (b) $E//b$ axis(c) Temperature dependence of planar Hall resistivity amplitude ($sin\phi$ term ${\rho }_{xy}^{\mathrm{chiral}}$) in ${\mathrm{WTe}}_2$ with current along different directions. (d) Temperature dependence of planar Hall resistivity amplitude difference between the $b$ axis and $a$ axis. It decreases for temperature higher than 100 K.