Abstract
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.
Highlights
WTe2 hosts unique transport phenom ena such as chiral anomaly,[6,7] unconventional quantum oscillations,[8] colossal magnetoresistance,[9] spin–orbit torque,[10,11] substantial spin Hall effect[12] and quantum spin Hall states in monolayers,[13] which opens a new era for physics experiments
As spin transport parameters in graphene are known to weakly dependent on temperature,[45] we identified that the decrease in unconventional charge-to-spin conversion (CSC) magnitude could be due to the increase in WTe2–graphene contact resistance at lower temperatures (Figure 3b upper panel)
The spin polarization created in WTe2 is shown to be utilized for spin injection and detection in a graphene channel in an allelectrical van der Waals heterostructure spintronic device at room temperature, which circumvents the problem existing in topological insulators for spin injection into graphene below 20 K.[20,21]
Summary
Topological quantum materials have attracted significant attention in contopology in the electronic band structures with an expected large charge-todensed matter physics and spintronic spin conversion efficiency. The spin polarization created in WTe2 is shown to be utilized for spin injection and detection in a graphene channel in an allelectrical van der Waals heterostructure spintronic device at room temperature, which circumvents the problem existing in topological insulators for spin injection into graphene below 20 K.[20,21] Such unique spin-polarized electronic states in Weyl semimetal candidates with novel spin topologies can be further tuned by tailoring their electronic band structure through enhancing their spin–orbit interaction strength, increasing the separation between the Weyl nodes through Berry curvature design, and controlling strain to break the crystal symmetry These findings in Weyl semimetal WTe2 for efficiently transforming the electric current into a spin polarization at room temperature is highly desirable for energy-efficient spintronic memory and information processing technologies.[56]. After submission of our manuscript, we noticed two very recent papers on the multidirectional and unconventional charge–spin conversion in MoTe2.[35,38] Our results on Weyl semimetal candidate WTe2 show an efficient and unconventional charge–spin conversion, which is different from conventional SHE and REE and demonstrates a practical approach for efficient generation and injection of spin polarization into graphene channel up to room temperature
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