Spin-Momentum Locking Induced Anisotropic Magnetoresistance in Monolayer WTe₂

Abstract

Monolayer WTe 2 is predicted to be a quantum spin Hall insulator (QSHI), and its quantized edge transport has recently been demonstrated. However, one of the essential properties of a QSHI, spin-momentum locking of the helical edge states, has yet to be experimentally validated. Here, we measure and observe gate-controlled anisotropic magnetoresistance (AMR) in monolayer WTe 2 devices. Electrically tuning the Fermi energy into the band gap, a large in-plane AMR is observed and the minimum of the in-plane AMR occurs when the applied magnetic field is perpendicular to the current direction. In line with the experimental observations, the theoretical predictions based on the band structure of monolayer WTe 2 demonstrate that the AMR effect originates from spin-momentum locking in the helical edge states of monolayer WTe 2 . Our findings reveal that the spin quantization axis of the helical edge states in monolayer WTe 2 can be precisely determined from AMR measurements.

Edge spin transport in the disordered two-dimensional topological insulator WTe$_2$

“…In WTe 2 , recent measurements of the spin quantization axis indicate that spin-orbit disorder is relatively weak. The canting of the edge state spin has been measured in experiments [61,62] in agreement with theoretical models [36,43,48,63,64]. These findings indicate that the spin quantization axis, although canted, does not vary strongly in position or momentum space.…”

Electrical Control of Spin-polarized Topological Currents in Monolayer WTe$_2$

“…From the band structure, we determined the Dirac velocity v F x = 0.7 nm/fs, the anisotropy parameter ζ = 0.2, the tilt velocity v T x = 0.4 nm/fs, and the pseudo Zeeman field B x = 0.7411 eV. From the spin-texture, we identify the SOC strength λ = 0.188 eV and a canting angle of ϕ ≈ 30 • , in agreement with other theoretical and experimental calculations [15][16][17]44]. It is important to highlight that the DFT results predict a persistent spin texture, indicated by the constant plateaux spotted in the shaded region, also captured by our simplified model.…”

“…Electrically controlled chiral spin currents. In WTe 2 the persistent spin texture defines the spin polarization direction in the QSH insulating regime [15][16][17]. To demonstrate that the electrically tunable PST enables full control of the spin polarization of spin currents (or canting angle), we determine the spin Hall conductivities using the Kubo-Bastin formula [46,47]:…”

Imaging current control of magnetization in Fe$_3$GeTe$_2$ with a widefield nitrogen-vacancy microscope

“…The details of the bulk crystals used for exfoliation can be found in Refs. [35,56]. For the non-contacted samples (main text figure 2), the FGT and WTe 2 flakes were picked up in sequence by PC (polycarbonate) films mounted on PDMS (polydimethylsiloxane) stamps and then released onto the diamond substrate coated with a Al 2 O 3 /Al grid as in Ref.…”