Unconventional Charge–Spin Conversion in Weyl‐Semimetal WTe₂

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.

Visualizing Tailored Spin Phenomena in a Reduced‐Dimensional Topological Superlattice

“…Such strong SOC materials usually are divided into two categories, heavy metals and quantum materials, for which the spin–charge interconversion is respectively attributed to the spin Hall effect (SHE) and the Rashba–Edelstein effect (REE), [ 1,2 ] or vice versa. Emergent topological quantum materials, including topological insulators (TIs), [ 3–6 ] Dirac semimetals, [ 7 ] and Weyl metals [ 8–11 ] —as the key core of quantum material families—have been compelling due to their order of magnitudes larger charge‐to‐spin conversion efficiencies compared to those in heavy metals. [ 12,13 ]…”

Charge-to-Spin Interconversion in Low-Symmetry Topological Materials

“…A magnetic field parallel to z causes spins to precess in the graphene plane but, according to and WTe 2 , including the persistent canted spin texture, 64 comparable results and efficiencies are expected in the latter, as borne out experimentally. 33,34,36 Our findings also call for a careful analysis of SHE measurements, since the interpretation of all-electrical detection in Hall bars 34,65,66 usually ignores the possibility of multiple spin Hall components. We show how the presence of canted SHE can be experimentally identified by reciprocal SHE, and how the different SHC contributions may be isolated in a spin precession setup.…”

“…15,16 When thinned towards the monolayer limit, they transition from the type-II WSM bulk phase to the quantum spin Hall regime [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] with strain-tunable topological gap. 32 Recently, large charge-to-spin interconversion (CSI) generated by the spin Hall effect (SHE) has been reported in multilayers of MoTe 2 and WTe 2 [33][34][35][36] with evidence of long spin diffusion lengths (λ s ). 34 The efficiency of the SHE is characterized by the spin Hall angle (SHA, θ xy ) which indicates which fraction of a driving charge current can be converted into spin current; θ xy depends on the magnitude of SOC and is typically no more than a few percent at room temperature in heavy metals.…”

“…43 These results represent the expected behavior in the monolayer limit of recent experiments performed on few-layer MoTe 2 33,34 and WTe 2 . 35,36 Such a peculiar spin response should become manifest in suitably designed nonlocal spinprecession experiments. 33,58,60,61 To probe this canted SHE, we propose the device concept pictured in the insets of Fig.…”

Two‐Dimensional Metal Telluride Atomic Crystals: Preparation, Physical Properties, and Applications

“…For 2D MTACs‐based Dirac and Weyl semimetals, the most of the Weyl semimetals focus on the MoTe 2 and WTe 2 , which display tremendous potential in producing big spin current because they have the spin‐polarized states with topological protection and can carry a greatly big current density. [ 113–115 ] Zhang et al. [ 116 ] reported that WTe 2 is a type‐II Weyl semimetal that has two special transport properties observed in a 2D WTe 2 nanoribbon.…”