Anisotropic Giant Planar Hall Effect in type-II Weyl Semimetals*

Recently, giant planar Hall effect originating from chiral anomaly, which is related to the chiral Landau levels, has been predicted and realized in nonmagnetic Dirac/Weyl semimetals. WTe₂ is considered to be an intriguing type-II Weyl semimetal with its Weyl cone tilted due to its broken inversion symmetry. Here, we report the observation in WTe₂ of the giant planar Hall resistivity that shows a B² magnetic-field dependences as predicted by theory. Most importantly, we observed a highly anisotropic planar Hall resistivity when the current flows along a- and b-axis of WTe₂. The planar Hall resistivity at low temperatures with current flowing along b-axis is almost twice of that along a-axis, because the chiral Landau levels and chiral anomaly are well-defined (or absent) when the magnetic field is parallel (or perpendicular) to the tilting direction (b-axis) of Weyl cone in WTe₂.