Abstract
We combined a spin-resolved photoemission spectrometer with a high-harmonic generation (HHG) laser source in order to perform spin-, time- and angle-resolved photoemission spectroscopy (STARPES) experiments on the transition metal dichalcogenide bulk WTe$_2$, a possible Weyl type-II semimetal. Measurements at different femtosecond pump-probe delays and comparison with spin-resolved one-step photoemission calculations provide insight into the spin polarization of electrons above the Fermi level in the region where Weyl points of WTe$_2$ are expected. We observe a spin accumulation above the Weyl points region, that is consistent with a spin-selective bottleneck effect due to the presence of spin polarized cone-like electronic structure. Our results support the feasibility of STARPES with HHG, which despite being experimentally challenging provides a unique way to study spin dynamics in photoemission.
Highlights
WTe2 is a well-studied semimetal belonging to the class of transition metal dichalcogenides
The quality of the Fermi surfaces is limited by the energy resolution of the high-harmonic generation (HHG) pulse, but still good compared to literature [22] and enough to distinguish hole pockets (hP) and electron pockets (eP)
We presented the first experimental STARPES study with an HHG source performed on WTe2
Summary
WTe2 is a well-studied semimetal belonging to the class of transition metal dichalcogenides. It has attracted a lot of interest since it presents a nonsaturating linear anomalous magnetoresistance [1], pressure-induced superconductivity [2], and it is the first proposed topological type-II Weyl semimetal [3]. The existence of semimetallic materials with symmetry-protected linear crossings of bands was pioneered by Abrikosov [4] and is predicted since long [5], but the recent reinterpretation in terms of topology provides a new point of view. Since Lorentz invariance is not a requirement for collective quasiparticles in condensed matter, one can have inequivalent velocities for the Weyl fermions along different directions as manifested by strongly tilted cones at the crossing states, which is what distinguishes type-II from type-I Weyl semimetals. To the related material MoTe2 [6,7], the expected number of WPs couples and their precise position in reciprocal space strongly depends on details of the calculations and on small variations of the buckled quasi-2D crystal structure, which makes us rethink
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