Intrinsic valley Hall transport in atomically thin MoS2

Abstract

Electrons hopping in two-dimensional honeycomb lattices possess a valley degree of freedom in addition to charge and spin. In the absence of inversion symmetry, these systems were predicted to exhibit opposite Hall effects for electrons from different valleys. Such valley Hall effects have been achieved only by extrinsic means, such as substrate coupling, dual gating, and light illuminating. Here we report the first observation of intrinsic valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS2, evidenced by considerable nonlocal resistance that scales cubically with local resistance. Such a hallmark survives even at room temperature with a valley diffusion length at micron scale. By contrast, no valley Hall signal is observed in the centrosymmetric bilayer MoS2. Our work elucidates the topological origin of valley Hall effects and marks a significant step towards the purely electrical control of valley degree of freedom in topological valleytronics.

Valley polarized current and resonant electronic transport in a nonuniform MoS2 zigzag nanoribbon

“…This leads to the valley Hall effect where the propagating electrons acquire velocity v ⊥ = − e σ J × Ω(K) perpendicular to the direction of the applied electric field that induces the current flow. Very recently signatures of the valley separation of the injected current 40,41 were measured in the microscopic MoS 2 Hall bar devices which followed similar observation for bilayer graphene 42 .…”

Highly Tunable Nonlinear Hall Effects Induced by Spin-Orbit Couplings in Strained Polar Transition-Metal Dichalcogenides

“…Moreover, the strong gate-dependence of D x in strained polar TMDs occur for Fermi level ∼ 20 meV measured from the conduction band edge. This corresponds to a relatively low carrier density regime (n 2D ∼ 1 × 10 12 cm −2 ), which has also been readily accessed by weak gating [39,40] without introducing significant displacement field. Thus, a dual-gate set-up is not necessary for detecting the gate-dependence of D x in strained polar TMDs, and we expect the gate-tunable NHEs in strained polar TMDs to be much more easily observed experimentally comparing to 1T d -WTe 2 .…”

External Environment Dependent Spin and Orbital Exchange Interactions

“…Spin-orbit interaction in two-dimensional materials brings many exotic phenomena to be explored. In transition-metal dichalcogenides, large spin-orbit interaction induced band splitting in both conduction and valence band gives rise to valley Hall effect [17,18] and unconventional quantum Hall effect [19,20]. Recently, band inversion caused by spin-orbit coupling proximity effect5 is observed in graphene/WSe2 heterostructure [21].…”