The research group of Professor Feng Miao of Nanjing University has made great progress in the research of WTe2, a transition metal chalcogenide with a layered structure, which has recently received extensive attention due to its experimentally observed giant unsaturated magnetoresistance. . The two crystallographic directions in the plane are perpendicular to each other (a, b axis), resulting in strong in-plane anisotropy due to the formation of tungsten chains in the a-axis direction. The research group took advantage of the layered peelability of WTe2 to obtain samples with different layers, and used the calibrated mask evaporation technology to fabricate high-quality WTe2 thin-film devices, and found that the ideal thickness of the samples for studying the chiral transport properties of WTe2 is 7 -15nm. The researchers observed a significant longitudinal negative magnetoresistance effect (the magnetic field is parallel to the current direction) in samples with the current parallel to the b-axis. The effect is very sensitive to the change of the angle between the magnetic field and the current. The effect is most obvious when the angle is completely parallel (the angle is zero), and the effect can be effectively suppressed by a small angle. The analysis shows that the longitudinal negative magnetoresistance effect is Caused by abnormal chirality. At the same time, the research group used the same fabrication process to prepare a sample with a current parallel to the a-axis (tungsten chain), and found that the chiral anomalous characteristic disappeared, which effectively verified the characteristics of WTe2 as the second type of Weyl semimetal.
       In the research of topological electronics, how to effectively control the topological transport characteristics is the key to realize the application. Based on the observation of the chiral anomalous effect, the research group took advantage of the gate voltage controllability of thin-film devices to realize the in-situ adjustment of the Weyl semimetal Fermi energy near the Weyl point for the first time, and realized the chirality in the WTe2 device. Field-effect modulation of transport properties. This work not only provides a universal experimental method for the in situ study of the second type of Weyl fermions in condensed matter physics, but also has important implications for the applied research of topology and chiral electronics. Juna Group provides WTe2 materials with excellent performance, which has made great progress in the research of materials.