Discovery of topological Weyl semimetals has revealed the opportunities to realize several extraordinary physical phenomena in condensed matter physics. Specifically, these semimetals with strong spin-orbit coupling, broken inversion symmetry and novel spin texture are predicted to exhibit a large spin Hall effect that can efficiently convert the charge current to a spin current. Here we report the direct experimental observation of a large spin Hall and inverse spin Hall effects in Weyl semimetal WTe2 at room temperature obeying Onsager reciprocity relation. We demonstrate the detection of the pure spin current generated by spin Hall phenomenon in WTe2 by making van der Waals heterostructures with graphene, taking advantage of its long spin coherence length and spin transmission at the heterostructure interface. These experimental findings well supported by ab initio calculations show a large charge-spin conversion efficiency in WTe2; which can pave the way for utilization of spin-orbit induced phenomena in spintronic memory and logic circuit architectures. Figure S1. Devices with WTe2-graphene heterostructure. (a) Optical micrograph of Device 1, with WTe2graphene heterostructure and ferromagnetic (TiO2 1 nm/Co 60 nm) contacts on graphene for detection and creation of (I)SHE in WTe2. The scale bar is 2 μm. (b) Atomic force microscope (AFM) picture of the heterostructure area (red mark in (a)). The inset is the thickness profile of WTe2 on few-layer graphene along the white dash line showing the WTe2 thickness is 27nm in Device 1. (c) AFM picture and thickness profile of Dev 3 (after the device burnout) showing WTe2 thickness to be 11 nm on monolayer CVD graphene.
An outstanding feature of topological quantum materials is their novel spin topology in the electronic band structures with an expected large charge‐to‐spin conversion efficiency. Here, a charge‐current‐induced spin polarization in the type‐II Weyl semimetal candidate WTe2 and efficient spin injection and detection in a graphene channel up to room temperature are reported. Contrary to the conventional spin Hall and Rashba–Edelstein effects, the measurements indicate an unconventional charge‐to‐spin conversion in WTe2, which is primarily forbidden by the crystal symmetry of the system. Such a large spin polarization can be possible in WTe2 due to a reduced crystal symmetry combined with its large spin Berry curvature, spin–orbit interaction with a novel spin‐texture of the Fermi states. A robust and practical method is demonstrated for electrical creation and detection of such a spin polarization using both charge‐to‐spin conversion and its inverse phenomenon and utilized it for efficient spin injection and detection in the graphene channel up to room temperature. These findings open opportunities for utilizing topological Weyl materials as nonmagnetic spin sources in all‐electrical van der Waals spintronic circuits and for low‐power and high‐performance nonvolatile spintronic technologies.
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