![]() The Fermi arcs are mainly along Y direction. a The calculated Weyl points and a possible Fermi arc in the k z = 0 plane of WTe 2 6, 13. However, experimental demonstrations of type-II Weyl fermions in WTe 2 have been unsuccessful owing to the limited resolution of angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy, which prevents direct observation of the tilting Weyl cone and Fermi arcs in WTe 2 8, 13, 14, 21.įermi-arc-induced Weyl orbit oscillations. Recently, it was reported that the decisive criterion for a type-II Weyl semimetal is the direct observation of its tilted band crossing in three directions in the momentum space, as demonstrated in LaAlGe 20. More specially, type-II Weyl fermions violate the Lorentz symmetry strongly 6, 20. Along the k direction that Weyl cone tilts toward, its kinetic energy is larger than its potential one in low-energy condensed matter physics 6. According to the definition of a type-II Weyl semimetal, a quasiparticle can be regarded as a type-II Weyl fermion that has the following characteristics. These Weyl points with opposite chiralities are possibly connected by Fermi arcs with a separation of 0.032 Α −1 along Y axis in momentum space (Fig. It was also predicted that there exist eight separated Weyl points in the bulk of WTe 2 and Fermi arcs on the (001) crystal surfaces owing to reflection symmetry. WTe 2 was suggested as the first material candidate for a type-II Weyl semimetal, in which the Weyl points occur at the crossing of the oblique conduction and the valance bands (Weyl cone tilts along Y axis in momentum space, Fig. A new quantum oscillation frequency originating from these Fermi arcs, observed in the Dirac semimetal Cd 3As 2, is also predicted to exist in ultrathin slabs of topological Dirac and Weyl semimetals 12, 19. In addition to having unique bulk state electrons and novel topological surface states, the so-called Fermi arcs also exist on these surfaces with broken inversion symmetry 6. Owing to the unique properties of these electrons in the bulk state (e.g., massless and defined chirality), other exotic physical properties have also been discovered, e.g., an unsaturated, positive magnetoresistance (MR) and an ultrahigh mobility of the carriers 5, 18. The three-dimensional (3D) topological semimetals, Dirac and Weyl, have been extensively investigated as representatives of a new state of topological quantum matter that, in the bulk state, possesses electrons with linear dispersion at the Dirac or Weyl points 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17. ![]()
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