Using the low temperature X-ray diffraction (XRD) at High Magnetic Field Laboratory, Chinese Academy of Sciences (CHMFL), a research group from Najing University observed Anisotropic Adler-Bell-Jackiw (ABJ) anomaly in Type-II Weyl semimetal WTe_1.98 crystals at the Quasi-classical Regime.

It provides experimental evidence of an anisotropic ABJ anomaly in a type-II Weyl semimetal.

Recognized as a remarkable phenomenon, ABJ anomaly originates from the breaking of chiral symmetry in the massless Weyl fermion under quantum fluctuation, which was mainly observed in high-energy particle physics and only recently in Weyl semimetals

The observation of negative magnetoresistance (MR) along the b axis in electrical-gated WTe₂ few-layered samples was reported recently.

Thus a natural question is whether one can dope-electrons into a WTe₂  crystal to observe the ABJ anomaly, more specifically, a permanent ABJ anomaly rather than a temporary one under electrical gating.

In this study, the team adjusted the Fermi level of WTe₂ delicately through electron-doping by adjusting the deficiency of Te and observed the anisotropy negative MR effect in the WTe_1.8 crystal.

They found that the temperature-sensitive ABJ anomaly is attributed to a topological phase transition from a type-II Weyl semimetal to a trivial semimetal, which is verified by a first-principles calculation using experimentally determined lattice parameters at different temperatures.

Theoretical electrical transport study reveals that the observation of an anisotropic ABJ along both a axis and b axis in WTe_1.98 is attributed to electrical transport in the quasiclassical regime.

Their work suggested that electron-doped WTe₂ is an ideal playground to explore the novel properties in type-II Weyl semimetals.

The work was supported by the low temperature X-ray diffraction (XRD) facility, a measurement system of the Steady High Magnet Field Facility (SHMFF) at CHMFL.

Their discovery have been published in Physical Review Letters with title of "Experimental Observation of Anisotropic Adler-Bell-Jackiw Anomaly in Type-II Weyl Semimetal WTe1.98 Crystals at the Quasiclassical Regime".

The temperature dependence of crystal structure change: (a) the XRD pattern for WTe_1.8 at low temperature of 35K (the inset shows the crystal structure); (b) the temperature dependence of lattice constants of WTe_1.8. (Image by ZHANG Lei)