Symmetry, spin-texture, and tunable quantum geometry in a 
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 monolayer

Shi, Li-kun; Song, Justin C. W.

doi:10.1103/physrevb.99.035403

Cited by 67 publications

(76 citation statements)

References 25 publications

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“…Discussion According to equation 1, the Berrycurvature must vanish in systems, which have both inversion-and time-reversal symmetry. The intrinsic breaking of the bulk inversion symmetry in WTe 2 along one crystal axis is predicted to induce a dipolar Berry curvature [13]. Phenomenologically, the anisotropic Berry curvature is consistent with the crystal axis dependence of our measured transverse photovoltage.…”

Section: Introductionsupporting

confidence: 86%

“…If timereversal symmetry is broken, a net Ω n can occur when integrating across the Brillouin-zone leading to a net Hall conductivity and a corresponding Hall voltage under applied bias. If inversion symmetry is broken, time-reversal dictates, that the net Ω n is zero, when integrating across the Brillouin-zone, but it can exhibit a dipolar structure where opposite points in k-space exhibit opposite Ω n (k) and opposite transverse velocities [1,13,14]. Hence the intrinsic breaking of spatial inversion symmetry promises few layer WTe 2 to host non-trivial Berry curvature re-lated transport phenomena on the Fermi surface such as the non-linear Hall effect [15,16].…”

Section: Introductionmentioning

confidence: 99%

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In-plane anisotropy of the photon-helicity induced linear Hall effect in few-layer WTe2

et al. 2019

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Using Hall photovoltage measurements, we demonstrate that a linear transverse Hall-voltage can be induced in few layer WTe2 under circularly polarized light illumination. By applying a bias voltage along different crystal axes, we find that the photon-helicity induced Hall effect coincides with a particular crystal axis. Our results are consistent with the underlying Berry-curvature exhibiting a dipolar distribution due to the breaking of crystal inversion symmetry. Using a time-resolved optoelectronic auto-correlation spectroscopy, we find that the decay time of the detected Hall voltage exceeds the electron-phonon scattering time by orders of magnitude but is consistent with the comparatively long spin-lifetime of carriers in the momentum-indirect electron and hole pockets in WTe2. Our observation suggests, that a helicity induced non-equilibrium spin density on the Fermi surface after the initial charge carrier relaxation gives rise to a linear Hall effect.

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Section: Introductionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

In-plane anisotropy of the photon-helicity induced linear Hall effect in few-layer WTe2

et al. 2019

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“…3 for ∆U = 10 meV. Our result demonstrates explicitly that Magnus Hall effect does not rely on Berry curvature dipole [26,[38][39][40][41][42][43] or the presence of skew scattering [44][45][46][47] that are necessary conditions for nonlinear Hall effect.…”

Section: Gate Gatementioning

confidence: 73%

Magnus Hall Effect

Papaj

2019

Phys. Rev. Lett.

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A new type of linear response Hall effect is predicted in time-reversal-invariant systems with builtin electric field at zero magnetic field. The Hall response results from a quantum Magnus effect where a self-rotating Bloch electron wavepacket moving under electric field develops an anomalous velocity in the transverse direction. We show that in the ballistic limit the Magnus Hall conductance measures the distribution of Berry curvature on the Fermi surface.

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“…In WTe 2 , non-symmorphic crystal symmetries (the b-c glide plane and c-axis screw) require that the spin responsible for generating τ B must have opposite signs in adjacent layers [13]. While β-MoTe 2 does not possess the same non-symmorphic symmetries, there is an effective in-plane polar vector at the β-MoTe 2 /Py interface that changes sign for adjacent β-MoTe 2 layers [35], which could lead to oppositelydirected current-induced out-of-plane spins in adjacent layers. Such a layer-dependent sign for the out-of-plane spin might lead to a partial cancellation of contributions from adjacent layers, and may have some bearing on this layer-dependent effect.…”

mentioning

confidence: 99%

Layer-dependent spin-orbit torques generated by the centrosymmetric transition metal dichalcogenide β−MoTe2

Stiehl

Gupta

et al. 2019

Phys. Rev. B

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Single-crystal materials with sufficiently low crystal symmetry and strong spin-orbit interactions can be used to generate novel forms of spin-orbit torques on adjacent ferromagnets, such as the out-of-plane antidamping torque previously observed in WTe 2 /ferromagnet heterostructures.Here, we present measurements of spin-orbit torques produced by the low-symmetry material β-MoTe 2 , which unlike WTe 2 retains bulk inversion symmetry. We measure spin-orbit torques on β-MoTe 2 /Permalloy heterostructures using spin-torque ferromagnetic resonance as a function of crystallographic alignment and MoTe 2 thickness down to the monolayer limit. We observe an outof-plane antidamping torque with a spin torque conductivity as strong as 1/3 of that of WTe 2 , demonstrating that the breaking of bulk inversion symmetry in the spin-generation material is not a necessary requirement for producing an out-of-plane antidamping torque. We also measure an unexpected dependence on the thickness of the β-MoTe 2 -the out-of-plane antidamping torque is present in MoTe 2 /Permalloy heterostructures when the β-MoTe 2 is a monolayer or trilayer thick, but goes to zero for devices with bilayer β-MoTe 2 .1 arXiv:1906.01068v1 [cond-mat.mes-hall] 3 Jun 2019Spin-orbit torques represent one of the most promising methods for manipulating emerging magnetic memory technologies [1]. When a charge current is applied to a material with large spin-orbit coupling, such as a heavy metal [2][3][4][5][6][7], topological insulator [8,9], or transition metal dichalcogenide (TMD) [10-16], a spin current generated through mechanisms such as the spin Hall or Rashba-Edelstein effects can be used to exert a torque on an adjacent ferromagnet. Recent work from several research groups has focused on understanding how a controlled breaking of symmetry in a spin-generating material / ferromagnet heterostructure can be used to tune the direction of the observed spin-orbit torques for optimal switching of magnetic devices [12][13][14][17][18][19][20][21][22][23][24]. For instance, the presence of magnetic order within a spin-generation layer can allow current-generated spin directions that are typically forbidden for highly-symmetric non-magnetic metals [17][18][19][20]. Similarly, our group has shown that by using WTe 2 as the spin-source material, a TMD with a low-symmetry crystal structure, it is possible to generate an out-of-plane antidamping torque [12,13] -the component of torque required for the most efficient mode of switching for magnets with perpendicular magnetic anisotropy, but forbidden in higher-symmetry materials. Only one other material, SrRuO 3 , has been shown to generate an out-of-plane antidamping spin-orbit torque [20], arising from symmetry breaking associated with magnetic order. Many questions remain regarding the mechanism and necessary conditions for generating a strong out-of-plane antidamping torque.In this work, we study the spin-orbit torques generated in TMD/ferromagnet heterostructures with a crystal symmetry that is distinct from WTe 2 i...

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Symmetry, spin-texture, and tunable quantum geometry in a WTe2 monolayer

Cited by 67 publications

References 25 publications

In-plane anisotropy of the photon-helicity induced linear Hall effect in few-layer WTe2

In-plane anisotropy of the photon-helicity induced linear Hall effect in few-layer WTe2

Magnus Hall Effect

Layer-dependent spin-orbit torques generated by the centrosymmetric transition metal dichalcogenide β−MoTe2

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