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

Abstract

By combining bulk sensitive soft-X-ray angular-resolved photoemission spectroscopy and accurate first-principles calculations we explored the bulk electronic properties of WTe2, a candidate type-II Weyl semimetal featuring a large non-saturating magnetoresistance. Despite the layered geometry suggesting a two-dimensional electronic structure, we find a three-dimensional electronic dispersion. We report an evident band dispersion in the reciprocal direction perpendicular to the layers, implying that electrons can also travel coherently when crossing from one layer to the other. The measured Fermi surface is characterized by two well-separated electron and hole pockets at either side of the Γ point, differently from previous more surface sensitive ARPES experiments that additionally found a significant quasiparticle weight at the zone center. Moreover, we observe a significant sensitivity of the bulk electronic structure of WTe2 around the Fermi level to electronic correlations and renormalizations due to self-energy effects, previously neglected in first-principles descriptions.Introduction -The observation of unconventional transport properties in WTe 2 [1], such as the large non-saturating magnetoresistance with values among the highest ever reported, prompted experiments and theory to address the electronic structure of this semimetallic transition metal dichalcogenides (TMD) [2][3][4][5][6]. WTe 2 consists of layers of transition metal (TM) atoms sandwiched between two layers of chalcogen atoms, similarly to other TMDs such as MoS 2 and MoSe 2 . Because of the layered structure, TMDs have commonly been considered as quasi-two-dimensional solids. The easiness of exfoliation down to a single layer makes them appealing for nanoscale electronic applications. WTe 2 has also been theoretically described, in a recent paper, as the prototypical system to host a new topological state of matter called type-II Weyl semimetal [7]. 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].

Spin zero and large Landé g-factor in WTe2

“…But, this is obviously not the case here, because the Fermi surface of WTe 2 consists of ellipsoids with mild anisotropy, which result from coherent electrons moving from layer to layer, as shown in [6,26] and our data. The transport is essentially three-dimensional [11,26]. In addition, the fact that SdHOs remain when the field is in-plane, θ=90°, rules out this scenario.…”

“…As SOC not only plays an important role in MR, but also is one of the key ingredients for the above topological phases, information on this coupling and its effect can provide a critical insight into these phenomena [24,25]. Since the calculated electronic structure is extremely sensitive to the atomic coordinates and electronic correlations in WTe 2 , experiments are particularly valuable in this regards [9,17,26]. Extensive ARPES and quantum oscillation studies have been carried out and four pairs of energy bands along the X-Γ-X direction have been identified, namely two pairs of hole bands and two pairs of electron bands, in agreement with first-principles calculations [3,6,26,27].…”

Nearly isotropic superconductivity in the layered Weyl semimetal WTe2 at 98.5 kbar

“…However, detailed analysis of the field angle dependence of the magnetoresistance at ambient pressure reveals a surprisingly low anisotropy [21]. If the anisotropy of the magnetoresistance is attributed to Fermi surface anisotropy, the electronic structure of WTe 2 is in fact isotropic, consistent with quantum oscillations [4,5,10] and angleresolved photoemission spectroscopy [10,11] data. With the isotropic electronic structure as the backdrop, it is natural to question the dimensionality of the superconducting condensate, which motivates the present study.…”

“…The discovery of an extremely large and non-saturating magnetoresistance in semimetallic WTe 2 [1] has generated considerable research efforts [2][3][4][5][6][7][8][9][10][11]. The interest is further intensified with the prediction that WTe 2 can be a type-II Weyl semimetal, in which Weyl fermions emerge at the border between electron and hole pockets [12].…”

k-resolved electronic structure of buried heterostructure and impurity systems by soft-X-ray ARPES

“…2013, Chen et al . 2018, verification of the topological fermions in Weyl semimetals (Lv et al 2015, Xu et al 2015, Xu et al 2017, Lv et al 2017, Di Sante et al 2017, Xu et al 2018, Yao et al 2019 and chiral topological semimetals (Schröter et al 2019); mixed dimensionality in topological insulators (Manzoni et al 2016); and many more. More examples of SX-ARPES applications to 3D materials can be found in previous reviews (Suga & Sekiyama 2013, Suga & Tusche 2015.…”