Evidence for topological type-II Weyl semimetal WTe2

Abstract

Recently, a type-II Weyl fermion was theoretically predicted to appear at the contact of electron and hole Fermi surface pockets. A distinguishing feature of the surfaces of type-II Weyl semimetals is the existence of topological surface states, so-called Fermi arcs. Although WTe2 was the first material suggested as a type-II Weyl semimetal, the direct observation of its tilting Weyl cone and Fermi arc has not yet been successful. Here, we show strong evidence that WTe2 is a type-II Weyl semimetal by observing two unique transport properties simultaneously in one WTe2 nanoribbon. The negative magnetoresistance induced by a chiral anomaly is quite anisotropic in WTe2 nanoribbons, which is present in b-axis ribbon, but is absent in a-axis ribbon. An extra-quantum oscillation, arising from a Weyl orbit formed by the Fermi arc and bulk Landau levels, displays a two dimensional feature and decays as the thickness increases in WTe2 nanoribbon.

Spin zero and large Landé g-factor in WTe2

“…However, the detailed mechanism underlying the MR has yet to be determined. Recently, theories have predicted WTe 2 to be a type-II Weyl semimetal in three-dimensional bulk form and a quantum spin Hall insulator in monolayer of 1T′ structure, which has further fueled the interest in this material [16][17][18][19][20][21][22][23].…”

Realization of Weyl semimetal phases in topoelectrical circuits

“…Since the linear dispersion around the WPs can be described by the Weyl Hamiltonian involving all three Pauli matrices, small perturbations do not lift the energy degeneracy but only displace the WPs in momentum space. Besides fundamental properties such as the massless and chiral nature of the bulk carriers and large carrier mobility [20,21], WSM states also exhibit unusual transport phenomena like the quantum anomalous Hall effect [22], large positive magnetoresistance [23], Klein tunnelling [24,25], chiral anomaly [26,27] and novel quantum oscillations [28,29]. These exotic features and inherent robustness against disorder make WSMs promising candidate for future generation nanoelectronics, spintronics [30] and valleytronics [31] devices.…”

“…For instance, carrier doping in WSMs may compromise the stability of the Weyl phases due to broken translational symmetry [38]. Additionally, it is usually difficult to achieve transitions between different topological WSM phases (Types-I, II, III) in a given material, and thus to form heterojunctions of WSMs of different phases [23,39,40]. There is hence a need for alternative platforms to realize gapless topological states.…”

Multiple Weyl and double-Weyl points in an elastic chiral lattice

“…Compared to Type-I WPs, it causes a particular density of states. Experimental observations of type-II Weyl fermions have been discovered in a layered transition-metal dichalcogenides [23][24][25] and a single crystalline compound [26,27]. For WPs, in addition to the linearly degenerate signature in all three dimensions, there are topological surface modes due to non-vanishing TCs.…”