Observation of large topologically trivial Fermi arcs in the candidate type-II Weyl semimetalWTe2

Abstract

We report angle-resolved photoemission experiments resolving the distinct electronic structure of the inequivalent top and bottom (001) surfaces of WTe 2 . On both surfaces, we identify a surface state that forms a large Fermi arc emerging out of the bulk electron pocket. Using surface electronic structure calculations, we show that these Fermi arcs are topologically trivial and that their existence is independent of the presence of type-II Weyl points in the bulk band structure. This implies that the observation of surface Fermi arcs alone does not allow the identification of WTe 2 as a topological Weyl semimetal. We further use the identification of the two different surfaces to clarify the number of Fermi surface sheets in WTe 2 . DOI: 10.1103/PhysRevB.94.121112 Transition-metal dichalcogenides (TMDs) have long been studied in many-body physics as model systems for metalinsulator transitions, multiband superconductivity, and charge density waves [1][2][3]. In recent years, the interest in TMDs intensified because of the promising optoelectronic properties of monolayer or few-layer devices based on hexagonal semiconducting MX 2 compounds with M = W,Mo and X = Se,S [4,5]. Unlike these materials, WTe 2 crystallizes in the orthorhombic, noncentrosymmetric 1T structure (P mn2 1 space group) and is semimetallic due to a small overlap of valence and conduction bands at the Fermi level [6,7]. Recent theoretical work [8] predicts that WTe 2 is an example of a new type of Weyl semimetal with strongly tilted Weyl cones that arise from topologically protected crossings of valence and conduction bands causing touching points between electron and hole pockets near the Fermi level. In type-I Weyl semimetals, realized for example in TaAs [9][10][11][12][13], the projections of opposite chirality Weyl points onto a surface are isolated from the bulk continuum and must be connected by well-defined Fermi arcs. This is not generally the case for type-II Weyl points, which are necessarily accompanied by bulk carrier pockets. The surface Fermi arcs corresponding to the bulk Weyl points in these materials can emerge within the projection of the bulk carrier pockets, rendering the robust identification of their topological nature challenging. Indeed, very recent angle-resolved photoemission spectroscopy (ARPES) experiments on the related Mo x W 1-x Te 2 and MoTe 2 systems report conflicting interpretations of the topological character of potential surface states [14][15][16]. ARPES studies on pure WTe 2 have to date not reported any surface states [17][18][19].In addition, WTe 2 is attracting interest because of its nonsaturating magnetoresistance [7] and the recent discovery of pressure induced superconductivity [20,21]. A possible relation between these phenomena and the topological nature of the low-energy surface excitations in WTe 2 is an intriguing prospect but has not yet been established. To date, even the basic bulk electronic structure underlying these phenomena remains controversial. The complex magnetotransport proper...

Universal scattering response across the type-II Weyl semimetal phase diagram

“…In this context, while a general consensus exists over the topological nature of the MoTe 2 arcs [20][21][22], the situation appears highly controversial for WTe 2 . Although surface arcs have clearly been observed in several photoemission studies, their topological or trivial nature is highly debated with different studies reaching conflicting conclusions [23][24][25][26]. Here, we visualize the response of MoTe 2 and WTe 2 and discuss the results in terms of Weyl nodes and Fermi arcs.…”

“…1(d [20][21][22][23][24][25][26][27]; (ii) The Weyl points are expected to appear at energies above the Fermi level [15][16][17][18], where they are inaccessible to conventional photoemission techniques [20][21][22][23][24][25][26][27]. In this context, while a general consensus exists over the topological nature of the MoTe 2 arcs [20][21][22], the situation appears highly controversial for WTe 2 .…”

Thickness-dependent electronic structure in WTe2 thin films

“…Bulk WTe 2 is predicted to be a type-II Weyl semimetal [13], in which Lorenz invariance is absent and the Weyl point appears at the boundary of electron and hole pockets [13,14]. This prediction has triggered renewed interest in this material [15][16][17][18][19][20]. In the monolayer limit, WTe 2 is predicted to be a topological semimetal in which both topological metallic edge states and 2D metallic bulk states are present [21].…”

Three-Dimensional Electronic Structure of the Type-II Weyl Semimetal WTe2

“…At odds with standard type-I Weyl semimetals showing a point-like Fermi surface, type-II Weyl excitations arise at the contact between hole and electron pockets. Theoretical predictions were immediately followed by several surface sensitive angle-resolved photoemission (ARPES) studies claiming evidence of topological Fermi arcs [8][9][10]. …”