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Gate-Tunable Negative Longitudinal Magnetoresistance in the Predicted Type-II Weyl Semimetal WTe2

The progress in exploiting new electronic materials and devices has been a major driving force in solid-state physics. As a new state of matter, a Weyl semimetal (WSM), particularly a type-II WSM, hosts Weyl fermions as emergent quasiparticles and may harbor novel electrical transport properties because of the exotic Fermi surface. Nevertheless, such a type-II WSM material has not been experimentally observed in nature. In this work, by performing systematic magneto-transport studies on thin films of a predicted material candidate WTe2, we observe notable angle-sensitive (between the electric and magnetic fields) negative longitudinal magnetoresistance (MR), which can likely be attributed to the chiral anomaly in WSM. This phenomenon also exhibits strong planar orientation dependence with the absence of negative longitudinal MR along the tungsten chains (a axis), which is consistent with the distinctive feature of a type-II WSM. By applying a gate voltage, we demonstrate that the Fermi energy can be tuned through the Weyl points via the electric field effect; this is the first report of controlling the unique transport properties in situ in a WSM system. Our results have important implications for investigating simulated quantum field theory in solid-state systems and may open opportunities for implementing new types of electronic applications, such as field-effect chiral electronic devices.