Amilcar Bedoya-Pinto
Weyl Semimetals(WSMs), materials with three-dimensional topologically protected electronic states, show highly interesting physical properties including surface Fermi-arcs, the chiral magneto-transport anomalyand extremely high electron mobilities. Still, its potential for device applications needs to be exploitedthrough the preparation of thin films, which would enable the design of functional heterostructures. Onepromising application field of WSMs is spin-orbitronics, as the Fermi-surface is expected to play an importantrole in the spin-to-charge conversion efficiency, according to theoretical investigations[1,2]. In this work, we report the growth of epitaxial, single-crystallineNbP and TaP Weyl Semimetal thin films[3]by means of molecular beam epitaxy, and their successful integration in spin-torquedevices. We have assessed the structural quality of the films(Fig.1a)featuring an atomically flat, ordered surface, essential for the observation of topological bandsby photoemission (Fig. 1b). Furthermore, werely on the preparation of high-quality in-situ TaP/Permalloy interfacesto investigatethe spin-orbit torques produced by the topological WSM by means of spin-torque ferromagnetic resonance (ST-FMR). First resultsof TaP/Py/MgO device structures at room temperature show readily signatures of largespin-orbit torques induced by the Weyl Semimetal: (i) a very strong symmetric component of the voltagelineshape across the resonancerelated to damping-like torques(Fig.1c), much different than the FMR responseof a reference ferromagnet, and(ii) a clear scalingof the resonance linewidth by applying an external DC bias through the bilayer(Fig. 1d). The connectionbetween Fermi-surface topology and spin-to-charge conversionis addressedby performing angle-resolved photoemission measurements on the TaP thin film surfaces prior to the in-situ depositionof the magnetic layers, and probing the spin-torque efficiencyalong the high-symmetry directions of theWSM, where the surface states areexpected to have asubstantialcontribution
[1] Sun, Y, et.al. Strong Intrinsic SpinHall Effect in the TaAs Family of Weyl Semimetals. Phys. Rev. Lett. 117, 146403 (2016)[2] Johannson, A. et.al. Edelstein effect in Weyl semimetals. Phys. Rev. B 97, 085417 (2018)
[3] Bedoya-Pinto,A.et.al. Realization of NbP and TaP Weyl Semimetal Thin Films, ACS Nano, 14, 4, 4405 (2020)